Ackerman

Rudolph Ackerman invented Ackerman Steering back in the days of horse drawn carriages. Monty Ackerman is my neighbor and an excellent basketball coach of 10 year old kids. While we can give Rudolph credit for the Ackerman Steering theory, Monty can help us to illustrate how the theory is applied.

When my kids were 10ish - my neighbor Monty was kind enough to volunteer to coach basketball. Monty had figured out the right way to teach kids and was a perfect role model for the little ones. He set a fine example for us bigger kids too. As a parent, I wanted my kids to work hard in hopes that they would become the next Michael Jordon. It seems in my enthusiasm, I would take youth basketball too seriously and applied my cheers in a less than perfect manner. I still remember today the glare from Monty when I vocally displayed displeasure with the teenage referees. Oh, Monty is a mild mannered man and while very rare, I know I had his glare coming. It is funny to look back and vividly see how too much of a good thing was a detriment. It is a bit embarrassing to me now but my support for my kids clearly went over the line. I wonder how many other parents go a little too far at the quarter midget track.

My goal in the basketball gym was to be supportive of my kids but, in implementation, I went way too far. Live and learn - sorry Monty! While Monty has nothing to do with the Ackerman Steering theory, he has everything to do with doing things in a balanced manner. His wonderful family exemplifies balance. When using Rudolf Ackerman’s principal, it pays to understand that everything has a time and place and using the “right” amount of steering encouragement will help your car go faster. Knowing when to use the Ackerman principle is even better.

Typical stock cars have a slotted adjustment on the Left Front for Ackerman Adjustment. The fixed bolt on the right shown here is planned out by your car builder in conjunction with the rack forward and aft mounting location. With the slotted LF adjustment moved back the tie rod end moves closer to the ball join center line the steering geometry speeds up how rar the left front spindle turns. Adjusting is simple yet chassis engineers should utilize "just enough".


Ackerman Steering as applied to stock cars is simply using geometry to make the LF tire turn farther and faster than the RF tire as the car is turned to the left which is known as Pro-Ackerman. The simple idea is that since the radius at the inside of the track is shorter than the outside it follows that the LF will follow a sharper radius than the RF. The sharper inside radius can create the need for more degrees of steering at the LF - that is the idea anyway. If you imagine a car with the steering wheel locked fully to the left it would drive in a perfect circle under power. The circle created by the LF would be smaller than that of the RF. Thus, more degrees of LF steering can make sense. The idea is similar to how rear stagger uses the LR tire and a smaller LR diameter to match the smaller arc found on the inside radius of the track.

You can think of stagger, rear steer and Ackerman in the same chassis category If you match up the Ackerman Steering theory and rear steer you could overcome handling characteristics at a given track. But - excessive stagger, Pro Ackerman and rear steer could be a recipe for disaster so moderation applies.

Anti-Ackerman can sometimes be used to your advantage as well. With Anti-Ackerman the LF turns less than the RF through a left hand turn. At times, we can use this geometry to make our cars faster.

The question is when does more LF steering (Pro-Ackerman) make sense? My answer is on smaller low speed track. If your track has a sharp steering transition in the center you might find a speed gain by using Pro-Ackerman. If your track is large with smooth sweeping corners then Pro-Ackerman will produce more negatives than it is worth. Remember our pal Monty – we want to avoid too much of a good thing. With Ackerman it is our goal to not go overboard. Under using Ackerman is better than using too much nearly every time. I wish I could go back in history and use a little less “enthusiasm” at the gym.

Pro Ackerman is shown in the drawing as the LF tire turns more than the RF. The idea is to match the LF arc to the smaller radius found at the inside of the track. Be sure to keep in mind the geometry changes as the car turns left while remembering to consider the steering changes as the wheel unwinds back to the right. Ackerman should be used in moderation but it can be the chassis seasoning tha makes your set up "just right".

On a stock car Ackerman is adjusted by using the slot on the LF spindle. With a rack and pinion steering system the tie rods run slightly forward from the rack out to the mounting point on the spindles. As you move the tie rod mounting point closer to the ball joints at the LF you speed up how fast the LF turns and you increase how much it turns. The concept is the same with a drag link and steering box.

A standard Pro-Ackerman amount is 2 degrees in 10 degrees of steering. In other words, if you turn the RF 10 degrees the LF would move 12 degrees. It pays to think about how the LF turns when using Pro-Ackerman. As you turn left, the LF turns more than the RF. As all things have an equal and opposite reaction you should understand that the LF turns back faster at corner exit as well. You can use the Ackerman effect to your advantage in the middle while turning left and on exit as you unwind the steering wheel.

In the northwest there are two tracks of similar quarter mile size yet, my thoughts on applying Ackerman are completely different. Wenatchee Valley Speedway was rebuilt by racing legend Garrett Evans. Garret is a racer and he rebuilt Wenatchee into a personal shrine to include new pavement and high banked sweeping turns. The playground for the kids and awesome viewing areas are added bonuses. The other track for comparison is South Sound Speedway which was revamped by the Behn Family. Butch Behn is an old school promoter and took a worn out old speedway and made it very cool. The million dollar stainless steel self cleaning toilets purchased from the city of Seattle for a few hundred bucks are a comical yet clean example of Butch’s wisdom. Both Wenatchee and South Sound are unique tracks. Similar size - but, completely different. These two tracks make good examples for describing when and how to utilize just enough Ackerman Steering geometry.

At Wenatchee, I was not a fan of Pro-Ackerman. In fact, I would prefer Anti-Ackerman when racing at the Wenatchee quarter mile. Wenatchee has a smooth entry into the corners and the car rolls through the middle if you have the car right. But, even with a fast car, the dynamics of turn 4 at Wenatchee could create a loose condition on exit. Pro-Ackerman would exemplify the problem. On exit and under power the rear tires would effectively push against the toe out created by Pro-Ackerman on exit. The scrub of front tires resists the power of the rear wheels causing the car to break loose late in the Wenatchee corners. At Wenatchee – if you could turn the car in the middle and get a straight shot off the car would hook up and be really fast. Pro-Ackerman could and does make the car loose at late exit as the LF front tire is turned too much under hard acceleration. For this reason Anti-Ackerman is a better plan at this particular track. Anti-Ackerman would slightly toe in the LF on exit. The small amount of Anti-Ackerman induced toe in would help the driver to unwind the steering wheel at late exit point. The right place at the right time applies here and the Anti-Ackerman affect would help the driver be smooth and hooked up on exit.

South Sound presented unique challenges and I would look at Ackerman in a different way. It is interesting to think about how tracks that look similar from the grandstands invoke a chassis set up mindset that is completely different. The South Sound challenge is that the driver needs to turn the wheel aggressively and quickly in the center. At Wenatchee you can drive through the center with a comfortable amount of steering input. At South Sound, drivers have to get after turning the wheel in the middle. The corners are not quite as rounded and the transitions are more abrupt. The groove relies on a big time pivot in the middle. I think the chassis challenges are that at Wenatchee hooking the car up at late exit was my goal.

At South Sound a strong pivot in the middle was comparatively more important. If the car pivoted in the middle it would take a nice set and be hooked up on exit. All tracks need a good pivot in the middle but at Wenatchee a good pivot can lead to late exit looseness. At South Sound a good pivot makes for a longer straight away and more over all speed.

The result is that Pro-Ackerman can help in the middle but might come at the expense of the exit. The trick is to use the Ackerman theory without creating the drawback or condition inherent in a given track. At the end of the day – zero Ackerman is better than too much. That said – the right amount can help cure a corner condition if the amount and timing are right. Ackerman has no affect on the straights and the geometry change increases with steering input. This idea can help you to have a stable entry as Ackerman change increases the more you turn the wheel. At entry the affect is minimal.

Depending on the track you can add extra Pro-Ackerman for qualifying. The thought is that you may be able to add “too much” Pro-Ackerman for 2 laps. The added LF toe out can build heat quickly in the LF for a qualifying run. Trial and error apply here but you could make the car loose on exit if you get to aggressive. If LF temperature is a problem at your track or if you run a high amount of wedge then a quick addition of Pro-Ackerman for qualifying can sometimes find you more speed.

Turn plates can be used to measure your Ackerman. Turn the RF tire 10 degrees and note how many degrees you have on the Left Front. IF the Left Front ends up with more than 10 degrees you have Pro-Ackerman. If the LF ends up with less than 10 degrees you have Anti-Ackerman.

Ackerman can be classified in your mental adjustment section with rear steer and stagger. The concept is that you are matching up the roll out of the left and right side tires by using one of these three adjustments. If you combine rear steer, stagger and Ackerman you can build a chassis package that line up the best benefits of each. You should guard against using too much of any one of these adjustment types and if you are being aggressive with all three you could be asking for trouble late in a run. If you time the dynamic movements of Ackerman and rear steer could find you a rocket ship set up. Go too far and your rocket will become an evil boat anchor.

Stagger is felt all the way around the track as the tire size is the same on the straight and in the turns. Rear steer occurs as the car rolls and Ackerman changes as depending on the degrees of steering input. You can imagine matching up the geometric change created by rear steer and Ackerman. Again – these options are best on shorter low speed tracks but they do have their place anywhere.

Thought about the Ackerman affect is usually confined to when the car turns left. In practice, it is equally if not more important to think out what happens to the car as the steering wheel unwinds. Often, Pro-Ackerman is used has a crutch to help the car turn through the center. Many times racers would be better off if they used other adjustments to help the car turn through the center coupled with using Anti-Ackerman to help keep the car hooked up on exit. I will take a car that is a touch snug in the center with a solid exit every time.

To achieve the most speed I think of stagger, rear steer and Ackerman as chassis seasoning. Just like a touch of salt on a good steak you can make your car feel better by adding a touch of seasoning to an already fabulous steak. Add too much salt and you are bound to upset the meal. While Rudolf invented Ackerman – we can learn from Monty and apply the benefits of Ackerman in a calculated, moderated and balanced fashion.

Go Forward – Move Ahead

Jeff Butcher

4/28/10

Set Up Routine

Pointing all four wheels the same direction is the way to find consistency and speed. Often I am asked what will happen if the rear end is out of square or if the bump steer is out of whack. The answer is, “I have zero idea”. When adjustments in your car are not right - there is no way to predict what will happen. I imagine the car will be erratic and it is likely it will feel different every time you get close to a corner. When you get to the track your car should be prepared. Completing every adjustment to your specs gives you the confidence to change wedge, stagger, shocks and springs without worrying if the car is loose because the rear end is crooked. Having the car set up with your numbers recorded is a needed part of your team’s efforts to build more speed each week and over the course of the season.

After a dominating performance in Phoenix, regarded engine guru Jim McFarland asked me, “So Jeff – your team just won the race. Do you really know how you did it?” Jim asked me this at the point in my career where I was starting to see success and was eager to learn. His simple question had a profound effect on me and I continue to learn from the question in the racing arena, in business and life in general. What Jim meant was that while it is great to celebrate a win, “do you know how you won and could you repeat the steps necessary to do it again?”

Jim taught me that having a plan that is sustainable is the way to increase the learning curve and was the key to ongoing success. Jim’s message was to enjoy success in the short term while understanding the adjustments and set ups allowing you to win again. We have all seen a one hit wonder and it is likely that those teams didn’t take the time to answer Jim’s question. Understanding your choices creates long term successes whereas winning by accident is like putting a monkey at a type writer until he spells a word. Keep the monkey off your back by understanding your chassis decisions. The concept is simple – plan to win. Plan to win in a repeatable fashion.

A set up plan will help you to build a race winning effort. In order to perform the set up routine the car needs to be completely ready to race. Full of fuel, everything done, full of oil, lead bolted down. Basically – after you finish the set up routine, the car goes in the hauler. When you reach the track it is ready to roll out of the hauler and onto the track. All fabrication projects are done and all projects are finished. Race ready means just that – ready to race.

I make sure everything is wrench tight before I take any measurements. At times crews measure with jamb nuts or bolts loose to speed the measuring process. When bolts/jamb nuts are tightened they can move rendering your measurements useless. It takes only seconds to loosen bolts/nuts and all measurements need to be taken with your components wrench tight.

Here is how I go about setting up an Asphalt Late Model in the order that I feel is best. I perform the set up process the same way each time and the car doesn’t leave the shop until my numbers are exactly right and written down. You may have another type of car but the concepts likely to be similar if compensate for your specific kind of racing.

Ride Height

I set the car on stands and use set up blocks to get the car up in the air with the wheels held at my ride height position. I do this on a level spot and mark the 4 tire locations on the floor so I can be sure the process is the same. If my floor is out of level I have already spent the time to shim the floor so everything is spot on. I spend the time to get the heights exactly right. Make sure to start with the race air pressure you plan to run along with your desired stagger.

Set the Front End

I set the lower control arms perpendicular to the frame and make sure there is a straight line that runs from the outer lower ball joints through the inner pivots. I then set the caster at the top as it seems most late models have the a-plates moved back to allow for adjusting on caster at the A-arm.

With the caster/camber, track width and toe set you can start the bump steer process. It is best to let the driver turn the wheel verses having them turn themselves over the bumps so I recommend running .002 out on the RF and .005 out on the LF. Setting the bump is time consuming but it pays back in consistent performance.

I then set my camber and adjust the toe with the car up on set up stands. From experience I would set the toe 1/16th in while on set up blocks because when weight was applied it seemed to come out about right. With the toe set, I would get going on the bump steer. I re-check the toe after I put the weight on the car and if I move the toe I re-check the bump steer. When weight is applied I get close to my 1/32 of toe out. Personally, I run .002 out on the right and .005 out on the left which is not much so I spend the time to get it right. It is okay if you use different numbers but because I chose to run a very small amount I made sure it was right and kept working until I hit those numbers exactly. Many car builders/chassis guys recommend more bump out and the amount you run is fine as long as it is repeatable and you understand what happens to the car under varying conditions. For me, I like the driver to turn the wheel and I see zero benefit of the tires turning themselves over the bumps. Most of our short tracks are rough thus my “choice” to run nearly zero bump steer.

Setting the caster and camber before stringing the right side allows you to line up the RF and RR Contact patches while taking your camber setting into consideration. A billet caster camber gauge has the machined precision needed for repeatable and accurate measuring.

Using a digital gauge for bump steer gives you accurate readings with out the need for doing math or watching 2 needles wind around wildly. This gauge has a reverse display for easy viewing and the billet tool is superior to sheet metal and tubing.

Square the rear end

My goal in squaring the rear end is to make sure that it is parallel to the rack and the inner pivot points of the lower A-Arms. I choose to run the lower control arms perpendicular to the chassis and make my caster adjustments on the top. In the end, the rear end needs to be square to the chassis and common sense prevails. I do square to the inner pivots at the front to eliminate the bends found in the mild steel that your car has been made from. Of course we start with a rear end housing that is straight.

First I clamp a perfectly straight edge to the bottom of the car 90 degrees to the straightest frame rail at the midpoint in the wheelbase. I verify that my inner pivots are parallel to the rack. On occasion I have to space the inner pivots a bit to account for frames that have bows in the mild steel. In the end, the Inner Pivots are parallel to the rack and the rack is exactly perpendicular to the frame. The Inner Pivots must be parallel to the rack or setting the bump steer will become a compromise.

Toe plates make quick work of setting your toe. With today's precision components I recommend running less toe out as compared to the past. If you have a rack and quality rod ends I would run 1/32nd or toe out to 1/16th of toe out. 1/8" or 3/16ths was the standard before but with better components we can run less and reduce rolling resistance for more speed.

I spend a ton of time getting my straight edge parallel to the Inner Pivot Line. Once I know my reference

straight edge is parallel I make sure it is 90 degrees to the frame allowing for the frame bows that are common. The frame rails are for reference and on average are square but I square to the front Inner Pivots and the straight line I created from that extends through the inner pivots through the outer lower ball joints. By squaring to the inner pivot reference line I am removing the variable of bows in the frame rails. With my straight edge perfectly located, I make peen marks in the bottom of the frame so I can set up my straight edge quickly next time. The marks come in handy when you need to check things at that track as I always carry the straight edge with me. While I maintain square to the frame I go the extra mile to and use the front inner pivot reference line.

I set my trailing arm lengths and adjust my trailing arm and top link angles. I set the J-bar heights and lock everything down. I line up the right side and ensure that my trailing arm and top link angles are correct. Most car builders line up the right side but you need to verify as if they want the RR set in ½” or something then you need to set the housing there to make sure your trailing arm angles line up with the brackets as intended by your car builder.

Line up the right side

Now that I have the straight edge to rely on I can quickly hook my tape and for fast 1 man measurements. I then set up a string on the right side of the car and line up the right side tires. I set the string at my frame height – some people do this different but frame height is something I can repeat the process and the method gets the contact patches in line. I set the RF straight and move the housing until all the string touches all 4 sidewall points on the right side. This method takes into account the camber setting you choose to run in the RF.

With the right side lined up I hang plumb bobs behind the housing as far out near the hubs as possible. A nut on the end of a string will work fine to hold the string tight. I hook my tape on the straight edge making sure the tape is running 90 degrees to the straight edge and take a measurement at each hanging string. I adjust as needed and check again. I repeat until I have it right on. Some people stop when they get within 1/32nd. I keep going until it is right on! Once I have everything tight and the rear end is square to my reference straight edge I recheck my right side string. If the right side no longer lines up then I move the housing until it does and start the rear end squaring again. Sometimes you have to go from the right side string to the rear end squaring multiple times. I only stop when the right side is lined up and the housing is exactly right.

Once complete I take an adjustable carpenters square and measure from the under slung frame rail to the RR brake rotor and record the number in my set up book. As long as the car isn’t bent I can get the left to right location with a quick measurement. By using the adjustable carpenters square, I have a nice quick check method to keep the housing located properly when track changes get fast and furious. The brake rotor is a straight and reliable reference point so the results are repeatable.

Moving on I get the lead in the car and set up my shocks and springs. Of course the car is already full of fuel and fluids. Once the car is at the minimum legal weight I move the lead until I have reached the allowable left side and my desired rear weight. For late models I set the lead and all weights with the driver in the car.

I set the stagger and adjust the wedge making sure the ride heights match what was used on my set up blocks. Every possible adjustment is recorded on my set up sheet and when I reach the track all changes are noted. At the end of each event I review my changes and record my thoughts about their success. I highlight adjustments where I felt I learned something new or if I overcame a particular problem successfully. I track my less than perfect decisions too as it is another opportunity to learn. I place my review comments in the same place in my set up book as over time I can review the notes and my knowledge base continually changes based on race experience.

Review

Set the ride height on set up stands

Set front inner pivot line straight through the lower ball joints

Set the caster at the top

Set the camber

Set the toe

Set the bump steer

Set the trailing arm and top link angles

Set the j-bar heights

Line up the right side – recheck the trailing arm angles

Square the housing to the inner pivot line

Load and adjust the lead – left side and rear weight

Install the springs and shocks

Set the stagger and air pressure

Set the ride heights

Set the wedge

Double check the front toe and adjust bump steer if needed.

Set the sway bar

Remember to understand and record your changes. When you win you will know how you got there and will find your way to victory lane again. Answer Jim’s question along the way and the monkey’s will stay clear of your back and jump on the backs of those that make accidental choices. A plan to win prevails and is a “choice” that is yours to make.

Go Forward – Move Ahead

Jeff Butcher

3/23/10

Under Pressure

Emotional pressure to find speed will be reduced if you manage your tire pressure with a plan. Every set up out there relies on the contact patch and getting the desired pressure at the point the rubber meets the road. Several important factors need to be considered for optimal tire pressure.

To achieve precise tire pressure readings you must have an accurate tire pressure gauge. Starting with the right gauge is paramount. Nearly all gauges are more accurate in the center of the range. For example; a 30 PSI gauge is going to be most accurate between 10 and 20 PSI. It will still work at 5 or 25 PSI but the percentage of error increases. For a 60 pound gauge you will get good results between 20 and 40 PSI. Just as before it will work fine at 15 or 45 PSI but the accuracy percentage goes down.

 Racing Tire Gauges with a Glow in The Dark dial face are a big advantage when it gets dark. There is a difference in glow coatings and better quality gauges have coatings that glow longer. You can recharge a Glow in The Dark Gauge quickly by placing it near any light source.

Since accuracy is best in the center of the range, you should choose a gauge that fits the pressure ranges for your type of racing. Gauges found for $10.00 dollars at the local auto parts store are designed for passenger cars and their percentage of error is too high for racing purposes. If your passenger car has 30 PSI instead of 32 PSI it is really not too big of a deal but on a racecar 2 pounds would be the difference between winning and kissing your sister. Choose a quality gauge that has less than a 2% accuracy tolerance. Obviously, better accuracy allows your team to slice information for repeatable performance.

 Larger tire pressure gauges such as this 4" gauge offer more accuracy. Larger gears allow for precision machining and the larger dial creates more resolution and better viewing angle. Rubber bumpers should always be included with racing tire gauges.

Digital Gauges
A quality digital gauge can give you better resolution yet you can be fooled by the digital display on a low quality version. Low quality digital gauges may post a number on the display but the accuracy must be supported by quality sensors for the display reading to be reliable. Digital gauges should have a backlight for easy night time viewing and the numbers should be large and easy to read. Digital, by itself, does not guarantee that the gauge will be more accurate. You may find a practical improvement as digital gauges remove the variable of viewing angle. Analog gauges can add to accuracy percentage error due to the viewing angle - the individual user’s interpretation of the needle verses the printed hash mark can cause a variation in results. A quality analog gauge will have minimal viewing angle error.

Digital Gauges can provide more accuracy but digital alone isn't the only factor. Quality racing gauges like the one shown is very accurate. Gauges with sensors designed for passenger car use are inexpensive but their low quality sensors are less than the standard required for racing.

Paying more for one digital gauge verses another does not guarantee accuracy but it can be a factor. There can be an accuracy correlation to gauge head size. If the display is very small then that could be a clue that the electronics contain low cost sensors. Digital sensors intended for passenger car use simply do not provide the resolution needed for racing. If a digital gauge rounds to half pound or even full pound you most likely find improved accuracy and quality with a gauge that reads in 1/4 pound or better digital increments.

Analog Gauges
For analog tire pressure gauges you will find many options. Gauge faces that have Glow in The Dark coatings are a big help when it gets dark. There is a difference in coating quality so take note of the manufactures that utilize longer lasting Glow coatings.

Analog gauge head size is a factor in assessing quality. In general, a 4” gauge will be more accurate than a 2” gauge. Larger mechanisms typically have more precision as the larger gears have the mass for easier machining. The longer throw on a 4” pressure mechanism offers smooth and steady needle movement resulting in improved accuracy as compared to a 2” version. With a larger gauge face the needle is easier to read and interpretation error is reduced as the larger circumference provides an expanded scale and improved visual perception of the enhanced scale graduations.

Liquid Filled Analog Gauges
There is a myth that liquid filled gauges are better. The mere presence of liquid does not ensure better quality. Liquid filled gauges may or not be good quality but the liquid alone is not the factor that guarantees accuracy. Liquid filled gauges work great to reduce needle vibration. If a gauge were to be mounted on a machine that vibrates then the liquid would help to reduce needle shake or bounce. Since tire pressure gauges are not used in a setting where vibration is an issue, the liquid serves only as a gauge damper. The liquid does absorb shock as the needle movement is controlled during gauge inflation. This dampening effect is desirable. Quality analog gauges have internal dampening systems without using liquid. Liquid is one way to provide dampening but dampening methods that do not utilize liquid are equally if not more effective.

Tire Gauge Care
Regardless of the type of gauge you use, it pays to take proper care of your precision tool. All racing gauges, whether digital or analog, should have a rubber bumper for protection. Ideally, you would never drop a tire gauge. Dropping tire gauges even one time can cause accuracy error potentially voiding the manufactures warranty. If you drop a tire gauge and that does not a rubber bumper then the shock is transmitted directly through the analog mechanism or digital sensor. Permanent damage can be the result. Rubber bumpers on tire gauges of any type are a must.

Using tire gauges properly is as important as selecting the right gauge. Over pressuring the gauge can and will damage your gauge. Let’s say a racer purchased a 30 PSI gauge to be in the center of the range for racing tires. On the way to the track the racer’s trailer gets a flat and our racer uses their racing gauge to check the trailer tires. The subsequent 60 PSI pegs the needle. In an instant it is more than likely that permanent damage has occurred to the racing gauge and the over inflation has destroyed the calibration. Care must be taken to not over load analog or digital gauges even one time. Tire gauges are precision instruments. Racing tire pressure gauges lead a hard life and the rough treatment introduces a decline in accuracy. Storing gauges safely during transport and on race night will provide for better long term performance.

Calibration
Many gauges have a fixed calibration and can not be calibrated in the field. Fixed calibration is held nicely for long periods of time if gauges are not dropped and are used within the required range.

If you have a gauge that can be calibrated you need to take it to a certified testing house or send it back to the factory for periodic calibration. Neither of these options is ideal. For racing purposes the most practical method is to simply purchase a second gauge and store it for the sole purpose of checking the calibration of your main gauge. Upon purchase – compare the two new gauges on and verify that they obtain the same reading on the same tire. If there happens to be a small difference simply record the difference and periodically verify that the gauge you use matches your master gauge and the original comparison. Use the master calibration gauge only for testing. Keeping a test gauge as a master is the most practical way to verify the accuracy of the gauge you rely on. You can compare your master gauge against you track gauge weekly as part of your set up routine.

If you use two gauges on one tire and both gauges give you the same result it is likely that they are accurate. While possible, t is unlikely that two gauges would be off by the same amount.

Adjustment
You can use tire pressure and your accurate pressure readings to adjust your car. For Bias Ply tires the air pressure can be adjusted to help your car get through the turns. Thinking out the adjustment options can help you maximize practice time or provide handling adjustability during pit stop races.

 Using an accurate tire gauge will help you match your contact patch for adjustability. Thinking about how air pressure affects contact patch size, stagger and sway bar load will give you more options to find the fastest set up.

It has been my experience that you can not stretch bias ply tires so it is important to buy tires that are the right size to begin with. Crews sometimes over inflate tires in an attempt stretch them. Measurements taken right after a tire is over inflated can show a larger circumference. The reality is that as soon as the tire gets hot the tire tends to return to the factory size. Consistency in your pressures at each corner on the car is critical too. Adding 5 pounds above your standard pressure to the RR in an effort to meet your stagger numbers is not recommended.

Purging your tires and using nitrogen can eliminate a "bad set" of tires. By reducing the moisture content in the tire through purging air is replaced my nitrogen. Moisture causes your tires to grow inconsistantly. Keeping the humidity in the tires consistant will help your tires to maintain their size. Filling the tire with nitrogen and draining it 3 times gets most of the moisture out. After 3 purges, the gain is minimal. A purge tool will allow you to preset the bleeder so you can clip it on and not worry about atmospheric air re-entering the tire after you have spent time on multiple nitrogen purges.

With Bias Ply tires I recommend staying within 2lbs of your standard per tire to dial in stagger. If you can’t get to your desired stagger within a 2 PSI window then your pressure and spring rate changes will be so dramatic that having the right stagger will not overcome the pressure induced spring rate changes. Over inflated tires create too much heat and premature wear. Check your tire sizes after mounting them and if they are not the right size then ask your supplier for another set. I am more likely to drop the left side tire pressures to help with stagger adjustments verses over inflating the right – it is a balance but over inflated tires do heat up in the center. Over inflation can cause over heating and stagger variations so it should be avoided.

To help your car handle here are some Bias Ply pressure tips

Car is loose everywhere:
Add Pressure to the RF which loads the sway bar for more cross weight.
Drop Pressure to the RR which reduces stagger, adds cross weight, and makes the RR footprint larger for more grip.

Car is loose off:
Reduce pressure at the RR which makes the RR footprint larger for more grip, adds cross weight, and reduces stagger.

Car is tight in the Center and Loose off:Drop the LR tire pressure. Drop the LF Pressure. The added rear stagger will help the car turn in the center. The larger LR footprint will help on exit. With both left side pressures being lowered the cross weight change will be minimal. The larger LF footprint will create more grip in the center helping the car to turn. Cars that turn better in the center have a better angle for the exit so often curing the center automatically improves exit issues.

Air pressure on bias ply tires is fine tuning tool and the adjustments work best when the car is already handling well. Fine tuning can be achieved and pit stop adjustments are more beneficial if your tire pressure gauge is accurate. Proper care and selection of tire gauges is the key to producing race winning accuracy.


Go Forward – Move Ahead

Jeff Butcher
Courtesy of JOES Racing Products
2/5/10
http://www.joesracing.com/

Corner Chemistry

Who is right - the driver or the crew chief? Since I spent my racing career as a crew chief I would like to say crew chief yet I know corner chemistry comes for understanding when to allow the driver to prevail as well as knowing when to let the crew chief earn his reputation. Teams would be much better off to focus on communication and leave the ego and need to be right for congress.

Our goal is to have fast race car that can win every time it hits the track. Racers are competitive and the desire to win can create tension. Time is short during practice and the intensity relies on good chemistry to avoid communication strain.

While this article relates to the driver and crew chief as separate people, many of the concepts and thought processes apply if you are a driver that fills the crew chief role on your own. Curt Spalding of AllStar Performance is a successful dirt driver that is regarded as an excellent chassis guy. Curt points out that many short track racers act as their own crew chief. For those of you in this category, it pays to break down the corner as if you were explaining handling issues to another person. When considering adjustments it is beneficial to get out of driver mode and think through the corner section by section.

The best driver/crew chief combos have learned to communicate in a respectful fashion and have practiced how to transfer information to accelerate the decision process. The word “team” applies and the set up for the week begins in the shop. Communication in the shop has the luxury of time so it pays to think about alternate adjustments while in the relaxed atmosphere of the garage and prepare some options if the baseline set up comes up short.

Crew chiefs can help their drivers by “accepting” driver feedback. One time I was helping a new driver and I think I could have listened better. The track was old, flat, and bumpy - just plain wore out. Portland Speedway doubled as a drive in Movie Theater and it was always funny to see the movie speaker stands in the infield. Anyway, at one time Portland was a track where I really struggled as a crew chief and through hard work and plenty of trial and error I found some corner magic. My “found” set up was proven with two different drivers and I think my teams won about 7 races in a short span during our tour stops. We were the car to beat – good times. Our set up was certainly different and it was fun to have the outside the box ideas win consistently.

When I went to Portland with a new driver I had my proven set up and the confidence that we would go there and with a great chance to win. We got there and the driver whined about the car the through the entire practice and I was so bent on past success that I didn’t adapt to his feedback. I “knew” I was right and the car would be fast. I think we finished 25th 2 laps down. I learned a lot that day – so much for being right. The driver has to be comfortable in the car and the past doesn’t turn the steering wheel. I should have cultivated his feedback and “fixed” the car so it was drivable for him and his individual talent. He was a winning driver and the car was a winning car. Communication issues took a winning effort and made it 25th. Given another chance, I would have mounted the wheels on the roof to make the driver happy. From that day forward my goal was to hear the driver and make him comfortable in the car.

So how do you build driver and crew chief chemistry? Respectfully listening would be a good place to start. From there it pays to be business like in your approach to driver feedback at the end of each practice session. A routine that is followed creates a business like approach will reduce emotion allowing for the information transfer to be complete. Helping the driver to be relaxed will help him to provide digestible information. Aiming for digestible information transfer is something to think about – it is hard to fix a car if the driver says it is loose in, pushes in the middle and then snaps loose off. Break down the corner and go in sequential segment order after every practice session. Tire temps are worthless when the driver has every bad corner condition going on at the same time.

If a car is loose on entry then nothing else in the corner makes any difference. How can the car be good in the middle if the driver is afraid to turn the steering wheel? If the entry is bad the middle will be a challenge too and the loose in condition just about always causes a push in the middle. Focus on the entry first and manage each section of the corner in order. I like to break the corner into 6 categories and work on making the car feel good at point 1 first. I then go to point 2 and so on. If I get to point 3 and make an adjustment that makes point 1 unacceptable then I must start over. The corner sequence has to be followed. If point 1 is off the rest of the turn will be less than perfect.

My first 5 corner points are the Braking, Turn In, Middle (Apex), Acceleration and Exit. Below are my definitions for these areas but your team can use their own terminology if it helps to get everyone one the same page? My 6th corner section is overall comfort and drivability. A focus on a drivable car saves equipment and makes drivers very happy.

Point 1 – Braking

The braking area is the corner entry point were the driver gets off the gas and is hard on the brakes. The car begins to turn with a small degree of steering input. NOTE: The car must never be loose getting or it will be a handful for the driver. Drivers can adjust for cars that are tight in the middle or loose off. Loose in means the driver will just have to go slower.




Chris Stephenson is shown entering the braking point at Sun Valley Speedway. Chris is able to take the car in hard setting him good position for the rest of the corner.

Point 2 – Turn In

The Turn in is the point in the corner where the driver turns the wheel and pulls the car towards the bottom. Maximum brake pressure is transitioning to minimum brake pressure and by the end of the area brake pressure is at zero. Keep in mind that at every track these areas change and the end of the turn in area is where zero braking is found regardless of the actual geographical place in the corner.



Brad Dahmer is shown pulling the car aggresively to the inside line. A stable entry allows Brad to pull on the wheel with confidence setting him up for a good run to the middle.
Point 3 – Middle (Apex)

The middle is the point in the corner where the steering wheel is turned to the maximum amount. The car will roll through the center point. Brake pressure is at zero and the driver picks up the throttle to some degree which will vary from track to track.

Jason Knaus nails fast time at Lacrosse Oktoberfest. Notice how the LF tire is lower than the LR tire in comparison to the white line – driver’s should aim for feeling the LF lower than the LR. Jason’s car is really cutting through the middle just about guaranteeing a hooked up exit. The middle is the point in the corner where the steering wheel is turned to the maximum amount. The car will roll through the center point. Brake pressure is at zero and the driver picks up the throttle to some degree which will vary from track to track.

Point 4 – Acceleration

The Acceleration area is the part of the corner after the point where the car has taken a “set” and is pointed for maximum exit speed. The driver gets on the throttle in can see the exit.

Michael Hasitngs is shown getting on the throttle. The car is pointed after rolling through the middle creating a fast exit. The Acceleration area is the part of the corner after the point where the car has taken a “set” and is pointed for maximum exit speed. The driver gets on the throttle in can see the exit.

Point 5 – Exit

The exit area is where the car transitions from partial to maximum throttle. Some tracks have a second apex where the car can become loose under full throttle. The car is still turning and the straight is clearly in view.

Lee Smith Action Photos
Jay Smith is killing the exit and his car is launching down the straight. Stock Car guys would enjoy this much grip! The exit area is where the car transitions from partial to maximum throttle. Some tracks have a second apex where the car can become loose under full throttle. The car is still turning and the straight is clearly in view.

Point 6 - Driver Comfort

Driver comfort is a paramount goal. Many times you can have a car with knife edge speed. These cars are hard to drive and often the added speed disappears when the tires get hot or in traffic. Often I have dialed out knife edge speed in favor of a car that is more drivable. Sometimes the knife edge can be used for qualifying but for late models a set up that allows the driver to drive aggressively will result in more speed over the long haul. If you have to compromise and an earlier corner segment is off a bit it is ok to tackle the corner condition that makes the car uncomfortable for the driver.

Keeping the car comfortable is your paramount goal. Michael Hardin is using all his skill to save the car from knocking down the fence. Steering clear of knife edge set ups saves equipment and makes racing in traffic much more fun for the driver.

Here is an example of walking the driver through the corner breakdown process - if you act as your own crew chief the breakdown is basically the same:

Entry:

Crew Chief: Can you drive into the corner and feel the car is stable?

Driver: The car gets in good.

Crew Chief: How about when you hit the brakes hard? Still ok – no loose in feeling?

Driver: Yes – it’s getting in good even if I over drive it in.

NOTE: I train my drivers to make sure the car gets in the turn so they can drive aggressively. My teams know loose in is just not allowed and we will go to any length to make sure the car gets in deep and with a stable attitude every time. I am happy to make the driver nuts asking repeated questions about corner entry as we must be sure any possibility of loose in is eliminated. Yes – this is worth repeating several times!

Crew Chief:
Ok – we are getting in good. How about the Turn In to the corner. Can you turn the wheel with out fear and pull the car to the bottom aggressively? Does the car take a set and cut well?

Driver: Yes – I can turn it hard on the Turn In – all good.

NOTE: I teach drivers to feel like the LF is always slightly closer to the white line than the left rear in the middle. If drivers turn the wheel and get the car on the white line with the LF lower on the track then the LR you know the car is cutting well and the angle to the exit will allow the driver to hammer the throttle.

Crew Chief: Ok how does the car turn in the middle?

Driver – The car picks up a push in the middle. It just doesn’t cut. When I pick up the throttle it gets tighter and then when I get to the exit it snaps loose.

Crew Chief – Ok, let’s work on the middle. How do you feel about a quarter inch of additional stagger and raising the J-bar an inch?

Driver – It’s already snapping loose off – won’t that make it worse?
Crew Chief – let’s get it rolling through the middle. If we get it to cut through the center it will be pointed down straight. The wheel won’t be turned as much so it will hook up when we approach the exit at the right angle. Let’s focus on the middle first and see if the exit gets better when the car turns through the middle better.

NOTE: A car that is just a little tight after rolling though the center is easy to drive and fast. A car with a push in the middle is no fun. A little snug can help with a solid and stable exit. A car that pushes will make for a loose exit that gets looser lap after lap.

There are a million scenarios and your team can work the corner conversation focusing on each segment in sequence. Move back to the start if an adjustment upsets a prior segment.

Teams should also keep in mind the big picture when it comes to chassis adjustments. Sometimes you have gone too far and the so called adjustment rules no longer apply. During these times you end up doing the opposite of what the book says. If the car has a push it is common to use less RF spring. But what if you have gone down to a 5 pound spring in the front and the push is still there? In some cases more RF spring would help the car turn better. If you have gone to an extreme or then the opposite approach should be considered. Your choice to use a softer RF spring to cure a push is based on going softer than a predetermined baseline. Maybe the baseline was off? Be aware of those times when adjustments are not making sense. Perhaps you have gone through the adjustment center and you may need to go the other way with your thinking.

If your team spends the time to find common terminology while taking a systematic approach in communication cornier chemistry will automatically improve. Breaking down the corner into segments will make it much easier for the drivers to communicate what they are feeling.

Be completely aware at all times that the car must get through each section in order. A car that is loose in will just about always push in the middle. A car that pushes in the middle is often loose off. Drivers can explain a push then be worried about the car being loose sending their chassis adjustments off in the wrong direction. The cure is to break the corner down and only move on to the next section when the preceding section is spot on. If a change sets back a prior corner section then start the process from the beginning. Corner chemistry will be built due to your systematic approach resulting in more chances to spray Champagne.

Go Forward – Move Ahead
Jeff Butcher
JOES Racing Products
11/09/09
http://www.joesracing.com/

Why We Race

A shimmering golden door hides a giant corporate machine that produces the next racing star of tomorrow. Once the door is opened the legendary machine guarantees racing fame and a long money filled career. Mesmerized, parents forget the comforts of home and stand in an endless line in hopes of placing their offspring in the proficient golden gadget located near a 2.5 mile oval Florida shrine. Reputation convinces parents to try and they are certain the elusive hardware will do all of the work instantaneously transforming their child into the next racing hall of famer. Nearly all youngsters would be better off honing their skills at their home track but Jeff Gordon, Tony Stewart and Kasey Kahne are rumored to be products of the wonderful machine. Jeff, Tony and Kasey know the golden door is a myth, yet history shows that the racing gods in Daytona Beach create new legends in lock step with the fall of an aging and once bright star.

Parents believe that when a young kid is given the key to the golden door the corporate machine can magically stamp out the next budding star of tomorrow regardless of their experience level. Many kids with whitened teeth and hair from the cover of Fashion Quarterly enter, but only one in a million emerges with the needed poise and skill of a true champion. With what seems to be an ever younger child inside, the pristine machine shakes, steams and vibrates working magic and applying mythical power to the chosen few. At last, a shot at the big time – it is all so easy or so says the legend.

Years ago I was at my home race track in Monroe Washington. Evergreen Speedway was located smack downtown and the grandstands doubled for racing and cow judging at the yearly fair. Richard Petty, Bobby Allison and Cale Yarborough were the racing gods of the day – corporate America allowed few gods back then. Legends in the era of black and white photography earned their time in the sun with actual grit, determination and plenty of beer.

By the age of ten I had been to the Evergreen Speedway many times. My dad would load me into his Chevy van with blankets to sit on and an Igloo cooler packed with his two beers hidden under a layer of ice and our PBJ sandwiches. Dad’s van was a true California special complete with crushed velvet seats and a stereo system that could rattle the windows out of an Army tank. Since we lived in Washington State, and not California, Dad’s ride really turned some heads. BF Goodrich T/A radials and 5 spoke mag wheels were the perfect accent to the airbrushed scallops that ran down the sides of the highly customized Chevy van. Riding to the track in style was a required part of racing back when I was ten. Mini vans weren’t allowed in the parking lot then. Little did I know I was learning why people race while chatting with my Dad on the 40 minute trip to Monroe.

We were regulars at Evergreen so even at ten I knew my way around. We sat in the exact same spot every week and nobody would even think of invading our turf. Eagerly, I would lead the family to the base of the grandstands turning left to look up at our favorite spot - 8 rows down from the top, 7 seats to the left of the isle and just past the start finish line. From there we had a perfect view of turn 1.

Turn 1 was where all the action took place and early in the year the turn 1 pond was still full - a beautiful combination of soupy water mixed with authentic northwest mud. Our bellies ached from laughter when drivers spun into the pond creating a giant brown splash. Thoughts of the billowing puff of steam filled the long Saturday night drive home with plenty of laughter. On special occasions, a rookie push truck driver would park too close to the pond and a muddy tsunami would cover his freshly waxed truck – real racing right here at home complete with material for America’s Funniest Videos.

Saturday nights weren't complete unless a couple unexpected racers got a shower in turn one. Racers that landed in the turn-one pond were usually unharmed. Mud on thier faces and bruised egos caused more damage than thier cars ever saw on the track.

Drivers and cars that landed in the pond were usually unharmed. The mud on their faces, a uniform dripping with puddle water, and egos that were more wet than bruised came standard with the admission price. The turn 1 puddle taught me plenty about why we race – it would just take me years to understand.

I fondly remember my favorite local drivers from back then. Real drivers that inspired me to get out of the bleachers and work on racecars were my idols. They had greasy uniforms, tussled hair and bad mustaches that would make them look more like adult film stars than racecar drivers. My visions resemble an old Elvis movie creating a dramatic contrast to current victory lane scenes with Kasey Kahne and his Budweiser Dodge sponsored by the Dodge Dealers in Gatorade Victory Lane at the Powerade Winners Circle celebration. Over the chaos of the celebratory noise you could hear Kasey say, “Which hat do I wear now?”

According to legend - in Kasey’s interview - he would utilize skills learned in the mythical machine. He would announce in his politically perfect voice; “I want to thank all of my sponsors, we had a really good car, the team worked super hard, the engine shop gave us a great engine and I am really proud of my team, my engineer, my PR guy, my mom and my dog”. It goes without saying that his dog is named “Charger”.

Amazing results - maybe the golden door really works! Sorry Kasey - I could have picked on anyone but since we are both from Washington I figure you would give me one freebie or maybe you would let me off the hook because my comparison to new and old is just “one of them deals”.

From our family Evergreen bleacher spot we could hear the announcer, well sort of. The thunder of the race cars muffled some of the words but back then my hearing was not yet hampered by the 100’s of times I would be in a closed garage with unprotected ears being bombarded with 8000 RPM’s and an engine guy that said he was setting the timing. I was never sure if the timing was set correctly or if it was just the engine tuners weekly playtime.

When ever the announcer mentioned my favorite figure eight driver I would perk right up. The loud speaker would crackle like an old scratchy LP - “….and starting on the pole - Dirty Dan the Sewer Man”. Funny how 35 years makes a reference to a sewer sound romantic.

Dan Knot was a racer. He raced for the pure fun. To him – Daytona was a post card with a white sandy beach and a bikini girl with oversize sunglasses. Mythical corporate machines not required. My Dad learned to be a chassis guy on Dirty Dan’s team and in true racer tradition he passed on all his knowledge to me. Dad taught me plenty.

Dirty Dan the Sewer Man somehow made a reference to a sew sound romantic. Dirty Dan (Knott) raced for fun - we all could learn from Dirty Dan.





My Uncle Bob turned wrenches on the Sewer Man’s car and he simply loved being around the track. Uncle Bob was a mechanic by trade. He could diagnose an engine simply by holding a screw driver over the intake - no need for one of those big fancy red boxes with a TV screen on it. Uncle Bob could simply listen to the engine and with the experience of real grease under his fingernails he could have you back on the road for a few bucks, a cold beer and a have a nice day smile – those were the days!

Dirty Dan had plenty of company. Ben Chandler, The Wizard, would add a certain color to the festivities making sure everyone in Monroe had something to cheer for. Crazy Carl Zaretske would smash the gas on and off through the turns of the Evergreen Figure 8 track. Carl had his trademark driving style. Whomp, whomp, whomp – you could hear the throttle pedal go to the floor about 8 times in each and every turn. To Carl, being smooth was saved for flirting with female groupies in victory lane.





Crazy Carl Zaretske was instantly recognized with his maroon 57 Chevy and the hand painted No. 2 on the side. Crazy Carl would stomp the gas on and off through every turn as he muscled his way to the front.






Why would Dirty Dan, Uncle Bob and my Dad race so hard when the mythical golden door and corporate machine was not even on their radar? Was it the time in the shop away from real life? Maybe it was the relaxation of building a mechanical marvel – figure eight cars were pretty cool! In what other sport can you dress in tacky oil stained uniforms and be rewarded with a crazed crowd that cheers wildly at every wreck, fist fight and photo finish? Perhaps it’s the camaraderie? The junior writer from the Seattle Times would just say it was for the love of the sport - he had no idea - the night before he was covering a high school chess tournament. Being low man on the totem pole meant he did all the bottom of the barrel assignments. Journalism at it’s best!



Maybe we race as the universal goal of competing creates a common racers’ bond – a bond so powerful that Saturday night at the track is more important than friends, weddings, anniversaries and kids birthdays. Respect strengthens the holding power of the Saturday night ritual and even the toughest competitors and bitterest of rivals treasure the compelling power of the racing bond. Every true racer feels remorse - but wouldn’t think of showing any sign of emotion - when their enemy’s auto show perfect machine meets with an untimely concrete collision.

Racing is so unique that it has its own language – mess with us and we will fire a warning shot - fool with us and we will take off your head. True racers can spend an entire evening in the shop and speak volumes with out uttering even one audible word. In a racer’s shop, there is a poetry of information that is often spoken with a single head nod, a curled eyebrow or a subtle shoulder shrug. Clattering wrenches keep rhythm with the cycle of the week – Saturday night comes each and every weekend during racing season.

Drivers too have their own silent language. Chrome horns spank the child in front of them and hand gestures wave a thousand messages to those passing by. A subtle right turn leaves a tire mark on the competitor’s door – a rubber zero clearly communicates the opinion for the duration of the night. Those who push the window too hard are given a firm squeeze into the outside wall shortening one day and lengthening six nights.

From the comfort of the crushed velvet seat in my Dads’ van and the fabulous puddle in turn 1, I learned that we simply race for fun. True racers know that just having fun is reason enough to sacrifice normal behavior in exchange for another Saturday night fix. Since we are all still ten at heart, why look for the fickle and elusive golden door and corporate magic? If we want clean fun we just need to remember Dirty Dan - he had fun – he found gold right here at home.

Go Forward – Move Ahead
Jeff Butcher
JOES Racing Products, Inc
10/09/09
http://www.joesracing.com/

Roll Center Magic

Dialing in your Front Roll Center could be the magic difference that makes your car prevail in the center of the turn. But, is it really magic? I think that many times we over analyze Roll Center when really it is just another adjustment. We throw springs at the car and make shock changes. We adjust the bite and stagger on a whim. Changing the Front Roll Center at the track is crazy talk – or is it?

For perspective – we often move the Rear Roll Center in a care free trial and error fashion. If the car is loose it is common for teams to simply move the Rear Roll Center down by lowering the panhard bar or j bar an inch or two. Teams on TV or at your local Saturday night track move the Rear Roll Center just for fun and then move it back if the driver doesn’t like it. We move the Rear Roll Center up and down and really do it with out over thinking.

When it comes to the Front Roll Center - it seems we have to consult witch doctors from Zimbabwe before we can think about making a change at the track. The misconception is that if a team were to change the Front Roll Center at the track then an ancient taboo would curse the team for the entire season.

The Front Roll Center is a point in space that is derived from the LF and RF Instant Centers and thier relationship to the contact patch.

Really, Front Roll Center adjustments at the track are easy if performed with a little thought and reasonability. There is no mystery and while we are happy to move the Rear Roll Center all over the place we seem to be afraid of Front Roll Center adjustments at the track. In actuality, you could consider lowering the Front Roll Center at the track to rid the car of a nasty push just the same as you would raise the panhard bar or j-bar to cure the condition? Really - you can. Just do it. If the driver likes the change then your team has found some new speed – if not then undo the adjustment with the same amount of thought as you put into moving the j-bar/panhard bar.

To help us become okay with making Front Roll Center trackside changes it pays to have a basic understanding of Roll Center both front and rear. Rear Roll Center is easy to understand as there is a physical part such as a j-bar or panhard bar for us to see. The Rear Roll Center is easy to calculate. Rear Roll Center is the average of the inner and outer mounting point heights at the center of the left and right mounting locations. Rear Roll Center may be easy to understand but in the end we just move it to adjust the car and then move it back if the driver complains. So simple.

The Front Roll Center can be confusing because on paper there are a bunch of lines going every which way. When the car goes through dynamic roll the lines go crazy as the pivot points move quickly which can give racers a headache – static front roll center is hard enough to comprehend but the data gets insane when you roll the chassis. But – what if we simplify the way we think about Front Roll Center? What if we view Front Roll Center like we view Rear Roll Center?

To simplify the Front Roll Center thought process it helps to understand the creation of the so called magical point. Front Roll Center is a calculated point verses a physical place. To find it you must first locate the Instant Center both left and right.

The RF Instant Center is found by drawing a line through the center of the RF upper A-Arm ball joint extended out though the center of the A-Arm inner pivot point on the frame. Another line is drawn from the RF outer ball joint center though the lower control arm frame pivot. The lower control arm line is extended out until it meets the upper control arm line. Where these lines intersect is called the Instant Center. The LF Instant Center is found in the same way.

Instant Centers are much easier to visualize than Roll Centers. The Instant Center is simply the point where the upper control arm pivot point and the lower control arm pivot point lines intersect.

After the Instant Centers are located you can now find the Roll Center. From the RF Instant Center you draw a line back to the RF contact patch center. From the LF Instant Center you draw a line back to the LF contact patch center. Where these two imaginary lines cross is the Roll Center.

Car designers spend a ton of time figuring out mounting points and control arm lengths to come up with their idea of the optimal Roll Center. That said – Roll Center is just a point in space and there is little preventing you from moving the Roll Center around to find more speed. Sure, you shouldn’t go crazy but you can make reasonable and common sense adjustments quickly at the track.

For example – let’s say your car has a push and you tried raising the Rear Roll Center to free the car up. The driver didn’t like the change and now you want to try something else. You could adjust the bite, add stagger, soften the RF spring etc. OR – you could lower the Front Roll Center. You could just change the Front Roll Center by thinking out the variables just like you do at the rear. At the track, you could simply raise the RF A-arm inner pivot point. Raising the RF inner pivot would move the RF Instant Center down resulting in the Roll Center moving down and over to the left. The result is similar to having a softer RF spring through the timing of chassis roll.

Increasing the angle at the RF upper A-Arm raises the Front Roll Center and moves it to the right.

In order for the Front Roll Center track adjustment to be practical, it pays to worry less about the detail of the specific Roll Center location and focus on the Instant Center and your goal for the chassis adjustment. If you use a RF A-Arm frame mounting plate that is slotted for height adjustment you can use slugs to ensure you have repeatable and documentable changes. The idea is that you when move the rear roll center down a half inch you have something solid and repeatable to record in your set up book. For the Front Roll Center adjustment you can simply record that you moved the RF inner A-arm mounting point up a half inch with a slug. By understanding Roll Center and all the magic lines you can use your understanding to simplify the process at the track allowing for easy and practical changes. Changing a slug is pretty easy for a trial run and it is easy to repeat. If the driver doesn’t like the adjustment you can simply bolt the original slug back in and look for the next piece of hardware to move in your quest for more speed.

When would you try raising the RF A-arm pivot which results in a lower Roll Center? All adjustments are about timing. When and how does the car roll and what effect can we have on the timing of the chassis roll to make things occur at the right point in the corner? The ultimate goal of knowing the specific time in the corner to have the suspension move is the ultimate set up secret. If we truly knew how and when things move in the corner we would always have the fastest car! Since we don’t truly know - we gather all the information we can find from drivers, pyrometers, data acquisition or whatever and apply our experience to cut down the trial and error process. Even the guys on TV, that have unlimited access to money and engineering, are still in the position of using trial and error.

You can think about a trackside Roll Center adjustment if you wanted the car to experience stiffer front springs under braking yet have the front springs feel softer in the center of the turn. In the end – your decision making is just like the rear roll center process. When do you decide to move the rear j-bar up or down verses making a spring change? A Front Roll Center adjustment thought process is basically the same thing. Just move it!

We can easily move the upper pivot point of the front A-arms to reach a desired goal. Again, trial and error is part of the equation but the mystery of the Front Roll Center shouldn’t stop us. Moving the A-Arm pivots at the track is easy if you have the right hardware. Slotted A-plates and slugs work great.



Using and A-Arm slug to adjust your A-Arm inner pivot points gives you an easy and repeatable way to adjust your Front Roll Center right at the track.
You can move the lower points too, but you bring in rack location issues and bump steer corrections. If you take the time in your shop and know which rack spacers and lower pivot slugs to use at the track you could bolt in the new slugs quickly giving you more options. Your options need to consider camber change curves, static settings and bump steer effects. Changing the lower angles relieve you of camber curve considerations but are more time consuming so a focus on the upper A-Arms may be the best trackside compromise?


A slotted A-Arm plate allows you to use slugs to make Front Roll Center Adjustments at the track giving you another weapon in your adjustment arsenal.
Lowering the RF A-Arm inner pivot raises the Front Roll Center and moves it to the right. Negative Camber is added and may need to be reset.

Raising the RF A-Arm inner pivot lowers the Front Roll Center and moves it to the left. Negative camber is reduced and may need to be reset.

Lowering the LF A-Arm inner pivot raises the Front Roll Center and moves it to the left. Positive camber is reduced and may need to be reset.

Raising the LF A-Arm inner pivot lowers the Front Roll Center and moves it to the right. Positive camber is added and may need to be reset.


An adjustable ball joint uses shims to change the A-Arm angle for quick Front Roll Center adjustments right at the track. A-Arm height an angle adjustments can be made just at the ball joint or in conjunction with inner pivot slug adjustments.

To further illustrate the point, I think that Front Roll Center is a design parameter that involves plenty of engineering and thought. I also think that if you have a basic understanding of Roll Center geometry that you can short cut the thought process at the track and simply focus on the LF and RF Instant Centers. At the track – you can easily visualize the effect on the RF instant center if you raise the RF a-arm inner pivot ½”. At this point in time you car is already “engineered” and you can just make the adjustment. By focusing on the Instant Centers you can readily make repeatable adjustments without having to worry about a bunch of imaginary lines. You can understand Instant Centers and their location quickly and easily. The reality is that Front Roll Center is simply a derivative of the Instant Center locations. Instant Centers are simple even through dynamic roll. Why complicate your trackside thought process with imaginary lines? Save the heavy thinking for the engineering room. At the track - just give it a try!

By understanding the Front Roll Center parameters and the imaginary points you can simplify the process and easily document which slug you are using to adjust your a-arms up and down. Focusing on Instant Centers makes it possible at the track. With this simplified thought process you can add another weapon to your adjustment arsenal and make adjustments that gets you ahead of your competition.


Go Forward – Move Ahead
Jeff Butcher
JOES Racing Products
10/01/09
http://www.joesracing.com/

Three Link Lessons

Have you ever driven a fork lift or other hot rod that had the steer wheel in that back instead of the front? Rear steer rigs turn quickly and the term “push” just would never apply. Understanding your three link suspension can give you adjustment tools to help you roll through the center of the turn or help to hook you up on exit.

In general your static rear setting should be dead square. In your shop you need to spend the needed time to ensure that your rear end is exactly square. Once your rear end is square it helps to record the measurement from a brake rotor to the frame as well as from the trailing arm brackets to the frame both left and right. Keeping these measurements on hand will allow you to make track changes with the confidence that you are maintaining a square rear end setting.

All of my shop set ups include a rear end that is absolutely square. It is always my goal to maintain a square rear end and use all the other adjustments to find the right set up. I always feel that changing the square is a crutch that can create late race handling problems and potentially make your late race tires under perform.

Clamp on aluminum trailing arm brackets allow you to set the trailing arm angles to help your car turn through the center. You can arrange your three link set up for over steer or under steer through chassis roll. Experienced crew chiefs use the three link set up as part of their set up package.


While I try to avoid messing with the rear end square it is an amazingly effective adjustment. Drivers always provide instant feedback and a rear end square adjustment is felt instantly. If you have a car that is loose in that condition must be fixed. Drivers can adjust their line for a center push or exit loose but entry loose means you simply have to lift sooner.

If you toe in your trailing arms at the front you can use the J-Bar to help over steer the rear end to cure a push in the middle. In this example, mounting the frame side of the J-Bar higher than the pinion side moves the rear end housing to the left as the chassis rolls. As the housing moves left the RR trailing arm gets longer and the RR tire moves back helping the car to turn.

If I have exhausted my reasonable loose in adjustment ideas I might choose to shorten the RR trailing arm an 1/8” to help cure the loose in condition. Often moving the RR ahead cures the loose in condition but you run the risk that the fix is short term. It is possible that you could get a late race center push or the loose in condition could return after the tires heat up and wear a bit. Experience at a given track plays a big role here.

On some days it seems that the push in the center won’t go away. Again, I try to avoid messing with the rear end square and go through all of my other ideas before moving away from square. To place this concept in perspective I would say 95% of the races I have ever been around in involved a square rear end. I would say I got a nice handling improvement about half the time that I moved the rear end and saw some or little improvement the other half. Hey, sometimes you miss the set up and it is what it is.

If the car has a push in the center then I might shorten the LR trailing arm 1/8”. It would be rare that I would recommend going more than an 1/8” and really I will stick with the thought that square is best 95% of the time – maybe even 98%.

You can think out your rear link set up and by understanding how and when the car rolls you can use the trailing arms to help dial in your set up. When using trailing arm angles to help your set up it pays to truly understand the movements at each section of the corner as well as think about any drawbacks that rear steer or under steer might create.

To help the car turn through rear steer you can run the RR trailing arm uphill a ½”- 1” at the front. As the car rolls the RR trailing arm will push the rear end housing back on that side. The uphill RR trailing arm adds anti-squat to the car which helps forward bite under acceleration so I like to run some uphill angle in the RR trailing arm. Maybe a ½” up is a starting point.

To really add over steer at the rear end housing you can mount the front pivot point of the RR trailing arm towards the center of the car. With the trailing arms toed in at the front you can use the J-Bar mounting angle to help steer the rear end through roll. If you run the frame side of the J-bar is higher than the pinion side the rear end housing moves left through roll. As the housing moves left the RR trailing arm gets longer and pushes the RR tire back producing rear steer that will help the car turn.

If you want the rear end housing to under steer then mounting the RR trailing arm level and perpendicular to the rear end housing will produce the desired result. As the car rolls the RR Trailing are will shorten pulling the RR tire ahead.

When it comes to trailing arms I try to avoid linkage arrangements that go though center under roll. In other words – if the trailing arm starts on an uphill angle I do not want it to go past level and then head downhill. If the travel was enough to create a down hill angle under full roll I would make an adjustment as this can make the care unstable. I want to avoid having the RR tire to move back and avoid having the trailing arm travel through level which would cause the RR to begin moving forward.

Typically, I like run the LR trailing arm up hill about ¾” to 1”. There is much debate on this but I like to have a little anti-squat in the car to promote bite under acceleration. If you run a high amount of wedge then level may be a better idea. Since the left side is lifting in the corner the angle increases and the LR trailing arm shortens and keeps moving in the same direction. Again, when it comes to trailing arms I try to avoid linkage arrangements that go though center under roll as going through center can create an unstable car.

Mounting the LR trailing arm with the inner pivots towards the center of the car coupled with the J-Bar running downhill from the pinion to the frame will pull move the LR tire back during roll promoting under steer.

By thinking out the trailing arm angles in conjunction with the J-Bar angle you can guide the rear end housing on the path that helps your set up through the turn. Running the J-Bar higher on the frame side will push the rear end housing to the left through roll. If you run the frame side lower or level the rear end housing will move right through roll. Using the J-Bar mounting angle to in conjunction with trailing arm angles both up and down and left to right gives you another tool in your arsenal helping you to achieve faster lap times.

A slotted pinion mount allows you to quickly set the J-Bar angle. Running the J-Bar higher on the frame side as compared to the pinion side moves the rear end to the left through chassis roll. Understanding how the rear end moves gives you adjustment options to dial in your set up for added speed.

Using trailing arm brackets with multiple trailing are mounting holes gives you additional adjustment options. The clamp type aluminum brackets allow you to mount the trailing arm left to right mounting location where ever you want. You can fine tune the trailing arm location and trailing arm toe settings by using spacers to set the left/right angle to meet your needs.

I recommend running the top link with a fair amount of anti-squat built into the adjustment and a downhill angle of around 4 to 7 degrees. If you run a track where the car is tough to hook up you can get some added bite to the LR under acceleration if you mount the top link closer to the LR wheel. If a track you run is consistently tight then mounting the top link closer to the RR will free the car up under acceleration.

A top link mount that is slotted will allow for ultimate fine tuning of your top link anti-squat settings. Top link mounts with multiple holes also work well. Adjusting the anti-squat for your car, driver and track can maximize exit grip getting your team to the finish line first.

Top link mounting ears with multiple holes or slots will give you more room for adjustability. You can choose mounting ears that have the adjustment holes offset behind the center line of the rear end housing which will add more anti-squat under acceleration. Keep in mind that anti-squat only takes advantage of the available grip through the use of mechanical leverage. Excessive amounts can cause a loose in condition or wheel hop. Occasionally the driver might report that the front wheels feel light under acceleration at the late apex point – if so you should dial back the top link angle and anti-squat for driver feel.

As a general guideline – more anti-squat in your three link suspension works best if you run low amounts of wedge. As wedge numbers increase then you should consider lower amounts of anti-squat. Again, you can make adjustments based on your set up. I prefer low amounts of wedge in an asphalt late model and most of the races that landed my teams in victory lane had 49% to 53% of diagonal. Based on those lower wedge settings I would run a fair amount of anti-squat. Typically, I would run the LR trailing arm up an inch on the front. By using the trailing arm with plenty of angle I could reduce the angle in the top link creating a more stable entry while maintaining the anti-squat I desired. If you run 60% diagonal then running the top link and trailing arm closer to level is a good starting point.

Using your three link suspension to dial in your car is a viable adjustment option that can be performed quickly right at the track. The teams that experiment with the proper three link set up can find the set up that launches their car off the corner with more acceleration to get to the checker first.

Go Forward – Move Ahead
Jeff Butcher
JOES Racing Products
09/01/09
http://www.joesracing.com/