Qualifying Secrets Revealed

You’ve spent all week tuning the car to prepare for the big race. Managing practice time and expensive practice tires is an important part of race weekend preparation. Practice usually centers on race set up and long runs. But, soon it will be time to qualify. During practice your team feels they have the car dialed in for race conditions and the driver reports the car feels great on long runs. Everyone on the team is happy as the consensus is that you have a good race set up for the car.

To get the most of practice and in race adjustments a good tire specialist is a must. JOES Racing Products Sales Manager and Gene Price Motorsports Tire Specialist Robert Osaki is a multi-championship winner. Rob brings the right tools to the track and meticulously cares for tire sets to 1/10 pound accuracy.

Since the car is fast and the competition in the pit area is staring at their stopwatches when your car is on the track, your team is confident that when the green drops that the car will be in contention for the win. In practice the car is fast on fresh rubber and when the “new” comes off the rubber the car is still fast in comparison to the competition. The race set up has been tweaked to find every ounce of comfortable speed.

Preparations begin for qualifying and a new competition begins. A fast car in practice is grand, but it is amazing how much can change during a qualifying run. You can only win the race if your qualifying time is fast enough to make the show – a front row start certainly helps your odds of winning.

Measuring corner speed helps to determine if qualifying tricks are increasing your corner speed. If you are scuffing qualifying tires in qualifying trim it is essential to record corner times and compare the corner time results to corner speed from practice laps in race trim.

At a big race, there are 40 cars and only 28 will make the A-main. Even with a car that grabs attention on practice time sheets – a good qualifying effort is needed to make the show. Fast practice laps mean nothing when the green waves for 2 laps of white knuckle driving to lay down a number to get you in the show. A fast car in practice that doesn't qualify well is insanely disappointing.  A green, white, checker for qualifying is intense and getting the most from qualifying takes the work of an entire team supported by clean and comfortable laps from your driver.

Replacing the practice set with qualifying sticker tires comes with risk. Bolting on a set of sticker tires will add speed to your well-tuned car – or so it is hoped. New qualifying tires should bring you more speed on the qualifying clock, but often the car is tuned so well on good practice rubber that too often something is lost when new qualifying tires are bolted on. Sometimes the change in the balance of the car is changed by new rubber and added speed that you hoped for from a new set over and above the practice set is lost in that unknown space where the single socks that come out of your Washer and Dryer are found.

During practice – the practice set has had plenty of runs and the stagger and tire pressures have multiple opportunities to be set to perfection. Now comes the sticker set - fresh off the truck and you have one shot at getting the pressure and sizes right to match the balance built with your practice session tires.

Over the years, I utilized a few tricks that helped ensure a good qualifying effort when the rules or race conditions required a new set of tires for qualifying. Often, rules allowed for scuffing the sticker tires which is the perfect time to test how the car would react in taped up in qualifying trim.

How you deal with tires and adjustments for qualifying is up to much debate and each crew chief has their own bag of tricks for Late Model Qualifying trim.

Matching up the tire sets from practice to qualifying is critical. Unfortunately, when you have a practice set and a qualifying/race set it is not always possible to match up the sizes exactly between your practice and race set. It has always been my philosophy that you can’t stretch tires to make them bigger – they are what they are from the factory and the size is determined at the time of manufacture. Too often teams measure tires after they over inflate them hoping they will grow to get the need stagger. While cold, the excessive pressure used to stretch tires does seem to make tires grow. But, then the tire gets hot and the anticipated growth in size from “stretching” disappears as it is an illusion and the balloon effect shrinks to the factory size as soon as operating temperature is reached. Often teams get got in this mistake. It is my belief that with bias ply tires that you have a two pound window to adjust size. If you can’t match sets up with 2 pounds plus or minus of tire pressure then you need to go to the tire truck and get the right size from the factory. Two pounds is the absolute maximum variation to adjust stagger as more than that changes spring rates far too much – I prefer matching practice pressures exactly and strive to stay within only a one pound variation.

If the practice set and qualifying/race set are different sizes at each corner then it is a good idea (mandatory) to drag out the scales and adjust the cross weight to equal the practice set cross weight. Two pounds of pressure changes wedge more than you think – just add two pounds the next time you weigh your car and watch the scale numbers go nuts.

Purging the air out of tires 3 times is a proven amount to get the most air out of the tires and replace it with moisture free nitrogen which limits heat induced pressure growth. A purge tool helps to drain air while preventing air from re-entering tires that have been purged with nitrogen.

Now it is time to decide how much nitrogen to put in the tires for the 2 lap qualifying run. Science and witchcraft come into play. Your practice tires were measured hot after a 10 or 15 lap run and they had time to grow to full pressure from heat buildup. The full pressure needs to be carefully recorded so you can have an idea of how much nitrogen pressure to run for your qualifying session.

Since qualifying is generally just two laps, I would be aggressive with adding pressure for qualifying runs as it was my goal to build heat fast. Ideally, qualifying starting pressure would be enough to get the tires “too hot” and pressure build up goes past ideal right at the exit of turn 4 as the car is headed for the checker. My goal would be to have all four tires come in at one additional pound than hot practice pressures. For me, this meant sending the car out with plenty of nitrogen pressure and the qualifying starting pressure would be only one pound less than my “hot” practice pressures – each team should experiment, but since it is a two lap run then adding pressure is a must.

A quality tire gauge that measures in 1/10th pound increments will help your team to make fine pressure adjustments to create repeatable speed.

Once the new qualifying set is matched up and the car has been re-scaled then the sway bar load can be adjusted to mirror your proven practice set up. Careful tracking of sway bar load is needed and re-setting the sway bar for a perfect match was mandatory with my cars that sat on the pole. The more notes taken with the practice set increases the odds that speed will be gained when new tires are bolted on for qualifying. Depending on the tendency of the car on a given day, I often added a touch of sway bar pre-load for qualifying to keep the car stable for the driver. I would vary the amount and add ¼ turn, a half turn or maybe even a full turn of sway bar pre-load. Other times I would just leave the sway bar the same as used in practice.

A quality sway bar mounting system makes it easy to add turns of sway bar preload as needed. You can put in load quickly and return it exactly to your baseline by keeping good notes.

Another “trick” to build quick qualifying tire heat in the LF is to add a ¼” bump washer on the LF tie rod end. For race set ups I run .004 to .008 bump out on the LF. A ¼” Bump shim adds bump steer – the extra grip from sticker tires cover the excessive bump from my race set up and the added bump action helps to get heat in the LF tire quickly – since it is a two lap run I have found that this little trick helps the car to cut in the middle for qualifying by getting heat into the LF quickly. I pre-measure the toe change from the ¼” bump shim installation in the shop so I know exactly how far to adjust the tire rod length saving time and ensuring I can get back to my race set up toe adjustment quickly. By doing the work in the shop – I save time at the track and am easily able to add the ¼” LF bump shim for a quick qualifying run. Your team may only want to add a 1/8” bump shim – trial and error work fine for this speed secret.

Adding a bump washer to create excess bump steer on the LF can build quick heat to help the LF stick during a qualifying run.

During qualifying, I know the driver is going to leave it all out there and the driver is counting on the car to stick. To allow for the aggressive qualifying run I add 1 turn of front brake for qualifying as an insurance policy preventing the car from becoming loose in as the driver piles the car deep in the corners for qualifying.  A little goes a long way and if you go too far with this insurance policy then you face making the car brake tight due to adding too much front brake. The idea is to add just a little as you know the driver is going to drive harder in a 2 lap run as compare to the smooth rhythm utilized in practice sessions.

Brake Balance adjusters with ball detents allow your crew to adjust the brake balance in quarter turn increments. Sometimes adding just a half turn of front brake helps the car for the aggressive laps turned in by top drivers.

 In addition to adding a little extra bump to the LF, I also toe out the front tires more for qualifying stability. I typically only run 1/32 or 1/16th of toe out for a race set up. For qualifying, I up the toe out to 1/8” on larger tracks and maybe 3/16” on small tracks. The added toe out creates stability for a two lap run and helps to build tire heat quickly.

Adding small amount of negative camber at the RF coupled with an extra amount of Positive Camber on the LF will help the car turn for 2 laps – just throw in a 1/16th shim as you want to add a little everywhere verses going nuts with one qualifying adjustment. The added camber would burn up the tires on a long run, but stickers will cut better for a two lap qualifying run.

Pulling the front bumper cover out as far as the rules allow (and then some) on the front side of the front tires gives you added down force at the front of the car. Down force always outweighs drag on tracks 1 mile and under. Adjustable fender braces make for an easy adjustment if your rules allow it. Stretch out the nose as far as you can to plant the nose.

Utilizing Adjustable fender braces allows your team to quickly pull out the nose flare in front of the front tires – the extra down force helps the front stick when new tires tighten up the car on a qualifying run. You can also pull in the quarter panels a small amount behind the rear tires to help the car slip through the air during qualifying.

To stick the nose taping off the front grill, brake openings and any ducts that cool the rear end or driver are a good idea. As much tape as possible is the rule with one giant exception. Short track teams run the same engine for many weeks if not all year. The teams on TV can bolt in new engines faster than you can change underwear. If you tape off the front so much that the car spits out water in a two lap qualifying run you have gone too far. Overheating the engine even once is not a good trade – be sure that enough air gets to the radiator for cooling. The small amount of cool air you let in the front will not slow your car down enough to risk engine overheating – let a little air in the grill opening. You can experiment with leaving the bottom of the grill open 1” or so and compare how the car reacts compared to leaving a 1” opening at the top of the grill. An opening at the bottom of the grill will pull in more air than an opening at the top of the grill.

All the above qualifying tricks help the front tires to stick. Go too far with these small adjustments and the car can become loose. Experience, testing and good note taking tell you which tracks are loose or tight for qualifying. Adjustments must consider the track characteristics so some of the tips have to be toned down for tendencies of a given track. Common sense and moderation go a long way here.

Extra front grip for qualifying gives driver the ability to turn the car under the hard driving needed to get in the show. New tires often tighten up the car so adjustments that keep the front tires digging into the track can make sense. Testing while scuffing a sticker set is really the best way to find out and these ideas should be added into your program. Every time sticker tires go on it is a good time to test the effects of qualifying trim. Confidence gained on a test run in qualifying trim will help your driver lay down the best number when it matters most.

To balance the ideas you used to plant the front tires you can use your adjustable rear spoiler supports to stand up the rear spoiler 2 or 3 degrees. The rear spoiler does more than most people think so just a few degrees of extra spoiler angle will help compensate for the front qualifying adjustments helping you to balance the extremes used for a two lap run. The idea is to stretch several adjustments to the limit due to the quick run. It pays to pre-set all of these suggestions in the shop and test them whenever you switch from good practice tires to a new set that can be scuffed in preparation for qualifying.

Twisting the spoiler supports to add rear spoiler angle can add needed rear down force for qualifying to keep the car in balance with the adjustments made in the front.

On small tracks such as quarter mile tracks – there is little reason to run a full load of fuel in a 22 gallon fuel cell. The fuel tank is up high and behind the axle. Moving the fuel weight into lower lead weight mounted low is a speed secret that really works well. If you don’t need 22 gallons to finish the race then lead in the low in the car will increase speed. There is no need to be a hero and you can run several gallons of extra fuel so you never risk running out. That said – you can move a bunch of swinging weight that is up high and behind the axle and use lead mounted low to increase the adjustability of your car. If you always run on a small ¼ mile track and only run 50 lap races then permanently installing a small tank will make your car more adjustable and will move swinging weight into lead blocks lowering your center of gravity. Safety first always prevails so if you run a full size tank on a light fuel load then always install approved bladder foam manufactured by fuel cell companies to fill the area created by a reduced fuel load. Consult your fuel cell manufacture and install approved materials.

These ideas are just suggestions – use a few of them or all of them. You can tone the suggestions down or get more aggressive based on your driver, track, car and local rules. Better yet, you can think of all the tiny improvements that will work with sticker tires for a two lap qualifying run. Those that drive the limit of aggressive adjustments will make gains in qualifying speed. Those that go too far will change the balance negatively and qualifying in practice trim could have worked out better. The teams that use tricks to climb the speed chart will find the secret to write your name at the top of the pole.

Go Forward-Move Ahead

Jeff Butcher

3/5/13

Durometers

Grip in the corners creates speed that will get you to the front. Fresh tires are the equivalent of bolt on speed.  In order to maximize grip, selecting the best tires will help you to get the corner speed you need to win more races. Since tires are a major investment it pays to spend some time ensuring that the tires you purchase are fresh – equally important is that your tires are consistent. Striving to find a “matched” set will increase overall speed. How often have you dialed your car in on practice tires only to have the set up change when a new set is bolted on? Could tire hardness variations be the culprit? If your series allows multiple compound choices then tracking the Durometer readings is critical if you plan to have speed at the end of the race.
A quality Durometer is a valuable tool that will help you to find more speed in any tire stack. Technology has provided the racing world with new tools that are more accurate and easier to read. Dial Type Durometers may still have their place; the pocket watch dial type utilizes a spring that transfers tire hardness to the face of the gauge.



A Dial Type Durometer can be purchased in a combo kit that includes a Dial Type Tread Depth Gauge. Using a Durometer is more effective if you use a Tread Depth Gauge and a Pyrometer to ensure consistency in your testing procedure.

Digital sensors are designed for accuracy and display giant numbers with resolution that gives you the extra edge. Digital displays provide an actual number taking the guess work out of reading a needle – the resolution is improved through both sophistication and viewing angle. Digital versions provide “relative hardness” that are easy to read even at night. The prominent display gives your team a modern advantage for only a few dollars more. The digital world that makes iPhones and computers available at reasonable prices has created mass produced sensors and chip components that indirectly improve the quality of all digital devices. Digital Durometers are benefactors of the digital world.
Quality analog versions work fine, but noticeable gains are made with new digital technology. The counter debate for the dial type is that they never need batteries and can sit in the tool box for long periods and always be ready to go.

 
Digital Durometers should include a back light helping you to see the accuracy even at night. Digital sensors benefit from the same mass production philosophies that make your smartphone and tablet cost effective.

Measuring tire rubber hardness is less exacting as compared to using dial indicators to measure the thickness of steel. Since you use hand pressure to push your durometer into the tire, it is common that 2 people can come up with different readings. As long as a dedicated crew member performs the task the same way each time then repeatable relative numbers will give you reliable information. The variance in actual accuracy will be limited how different crew members apply pressure. Eliminating variables will provide the best results with both Analog and Digital Durometers. Experience and feel will be enhanced by utilizing a measuring process that eliminates as many variables as possible. With training, all of your crew members should be able to produce the same readings.

Rubber deforms and the best readings are obtained when you take readings quickly – if you allow the Durometer to sit in one spot, the specially sized Shore A measuring probe will sink into the tire surface. The tire rubber deforms around the Durometer measuring probe. If you leave the Durometer in place for 30 seconds on one tire and 3 seconds on the next, your readings will suffer and accuracy is lost.
The best way is to ensure the tire is free of debris - a scraper should be used to remove loose rubber unless you are measuring the hardness of sticker tires.

Place even pressure and take care to hold the Durometer flat on the tire. Flat positioning on the tire creates the best results. It is a myth that rolling the measuring pad on your Durometer over the tire provides better readings, in fact “rolling” introduces un-needed variables. Simply holding your digital Durometer flat, with consistent and light pressure for a consistent time period provides the best results. Just set it on the tire with consistent finger pressure and measure it – simple replaces complicated every time. Doesn’t it make sense that holding a measuring tool flat on an even surface will provide better accuracy than rolling the Durometer over the surface? Why introduce a moving target by rolling a flat surface over the face of the tire?



Using a Durometer is simple – consistency is key to producing repeatable results. Simply place the Durometer flat on the tire surface with moderate finger pressure. Rolling adds a variable so just set the thing on there and take your reading within a second or two – easy.

 Really, measuring tire hardness with a Durometer is a simple process. Marketing hype is replaced by utilizing a simple repeatable process each and every time. Use the finger guide located at the top of the Durometer, provide light and consistent pressure, and verify that the durometer is flat on the clean tire. Then, take readings quickly and take 1 second +/- for the Shore A probe on your Durometer to stabilize – for the best results, be sure to time the measurement so that each measurement is taken with the Durometer foot pad on the tire for the exact same amount of time. Consistency is what will produce “Relative Hardness” that can be recorded to produce real results for future use.

If you set the Durometer into the tire and hold it in one place you will see the hardness number will rise - then as it is held in one spot the reading will start to drop. Hold the Durometer in one place too long and you can be assured that the Durometer measuring probe is sinking into the tire providing you with erratic results. Experiment by holding the Durometer in one spot on the tire for several seconds and you will visually see how the Shore A probe deforms into the tire – the longer you hold the Durometer in one spot – the more you can watch the reading drop as the probe is simply sinking deeper into the rubber. The process is simple – make sure the Durometer is flat on a clean tire surface and with even pressure simply record the reading. You can save rolling around for other more exciting endeavors.

Creating a repeatable process will give you the best relative hardness numbers and give your team the best chance at recording accurate readings. You must start with a clean tire. In the case of testing new tires, you can avoid worrying about debris or rubber build up. New tires are easier to test than used ones. When testing used tires, ample time must be spent cleaning the area to be tested. A flat scrapper easily removes debris off of hot tires that just finished making a few laps. Used cold tires have debris build up that has solidified on the surface. The rough texture will give you erratic results. Be sure to put some muscle on a scrapper on cold used tires. With a little effort you can witness the embedded loose rubber falling to the ground revealing the actual rubber surface that connects your chassis to the contact patch.

Several spots should be checked on the tire as tire rubber is not perfectly homogeneous (some areas of every tire are harder or softer than others). Small areas in the tire can be harder than others and the variation in the rubber surface must be averaged out. The rubber surface can be uneven creating variances. I check an area on the tire in 3 to 5 places. I always throw out the high and the low and then look for a hardness number that comes up to the same reading in several locations. If the tire is hot after a run it will pick up loose bits of rubber on the way into the pits – use a scraper to get down to the “real” tire rubber surface. The same theory applies to checking tread depth – you want to measure the real tire surface and avoid all the loose debris that can skew the readings.

Since rubber becomes softer as it is heated it is critical to measure the temperature of each tire before taking the Durometer reading. If you have two tires with the same compound and one is 100 degrees and the other is at 50 degrees the cooler tire will read significantly harder. You could warm up the same 50 degree tire to 100 degrees and find that the Durometer readings would equalize. To check Durometer readings you must have tires that are equal in temperature. Even one tire measured on the shady side will read harder than the side facing the sun.

 
Pyrometers are a must when measuring Tire Hardness. You can use an IR Pyrometer to check the surface. A probe type with an adjustable probe is really the best tool for checking tire temperatures (see the JOES Knowledge Center on the JOES website for Pyrometer Tech).

Tracking tread depth in conjunction with the tire hardness will allow you to predict when a new set is in order. By measuring the remaining thickness of the rubber on a new tire you will gain insight as to when a tire will lose adhesion. By diligently tracking tread depth and recording Durometer hardness through wear, you will be able to identify when it is time to hit the tire truck and step up for a new set. Over time you will learn the wear patterns and the Durometer will visually show you at what depth your specific tires give up.
Heat cycles need to be factored into the Durometer measurement process as well. Racing tires come out of the factory with a magic mix of chemicals that produce grip. Tire engineers work tirelessly to ensure your tires maintain maximum grip for the maximum time. Chemical engineers mix their recipe of friction producing materials and chemicals into the tire to give long lasting and repeatable grip. Each heat cycle “evaporates” valuable chemicals out of the base rubber. With each run, the tire becomes harder and the chemicals that keep the rubber soft and pliable are lost. Your Durometer can help you find the point in time when performance drops off. Variables such as tread depth wear, heat cycles, number of laps, age, ambient temperature all factor into the tire replacement schedule.

 If you know you have a loose car and have been buzzing the RR all day then you must consider that the RR will have faced more abuse than the other tires. Understanding why tires get hard is a compilation of several variables.

Top teams keep notes on their tire sheets so they can save money by running tires longer (Download Free Tire & Chassis Sheets at http://tinyurl.com/8gu92hj). Detailed tracking of variables provides valuable warning allowing for a purchase of a new set before they quit mid-race. Your rules dictate specific variables and if you run the same set for more than one week you can save some money, without sacrificing performance, by utilizing the results of your Durometer tracking. If you buy a new set each week you can learn which tire serial numbers perform best and cull out any old or bad tires hiding in the at your tire supplier.

Durometers can be used to predict the end of life on tires that are run multiple times. If you run a weekly series and your tires are run for more than one week it can be very valuable to track the tire hardness. Finding a good used matched hardness set from your inventory will help you to have good practice tires.
By understanding the wear characteristics, racers can use science to determine when to purchase a new race set or practice set. Tracking the tire hardness of used tires will give you data that can be used to graph when they are too hard to achieve the best lap times. Often, race tires perform to a lesser degree even when the wear indicators show there is substantial rubber left. While there may be rubber left on the tire the chemical compounds have evaporated due to multiple heat cycles leaving the remaining rubber too hard to create need temperature and friction.

Friction creates heat. More friction – more heat. Using a Pyrometer alongside your Durometer is mandatory. If you have apples to apples wear and you go on a 5 lap run - then all things being equal you should have Pyrometer readings that are reasonably close from the two sessions. If your set suddenly looses temperature as compared to the prior run you can be assured the friction is being lost. The tire is getting harder and the chemicals that create grip have evaporated out of the tire. Tracking tires goes beyond hardness. Paying attention to all of the variables that affect your tires creates the best performance.

Hardness measurements are most valuable when used systematically with pyrometers and tread depth gauges. Lap counting and heat cycles all come into play. Maybe heat cycles are the critical factor for your brand of tires, but maybe simply checking wear depth with let you know when a new set is needed. Durometer readings will back up your concerns and the Durometer will show the relative hardness if readings are taken at equal temperatures.


Careful and consistent measuring utilizing several tools will help you to create a system that produces repeatable results. Shopping is a good idea here.

Digital Durometers are the new revolution and are only a bit more in cost. Soft tires at the end of a race could give you the added grip off of turn 4 taking you to victory lane. You can still type a letter with a typewriter, but with computers the results and time savings are vastly improved. The digital revolution is here to stay. Dial Durometers work fine when used properly and never need batteries. A Digital Durometer used properly will create an easy to read number and the backlight allows you to see your winning resolution even at night.

Tracking tire hardness with a repeatable system will give you the resolution to gain an advantage. Utilizing a Dial or Digital Durometer in conjunction with a Tread Depth Gauge and a Pyrometer will give you all the tools needed to produce consistent and recordable results that will give you the winning advantage as it relates to the theory of relativity.

 Go Forward – Move Ahead.
Jeff Butcher
 05/05/13

T-Nut Power

Gaining horsepower by utilizing parts that reduce resistance has never been more important. In all actuality, these resistance reductions don’t really gain horsepower – they just use up less of the available power that you have. Efficiency is vital and anything you can do to add to your coast down horsepower will make for faster lap times. With any race car, any improvement in coast down horsepower is going to be a benefit. The benefit is magnified if you have a motor rule that limits horsepower or run a crate motor.

Just what is “coast down horsepower?” If you have a safe hill nearby you can measure your coast down losses by letting your car roll down the same hill with the engine off. Literally – you just mark the starting point and let the car coast down a safe hill and see how far it rolls until the gravitational energy of the hill is expended – you then mark your end point. Your car will coast until gravity slows your car to a stop. You might have trouble finding a safe hill, but if you do you can get a bench mark and return to the hill to measure your coast down gain – you can track the extra roll in feet every time you find a resistance reduction. Aerodynamic savings and mechanical rolling resistance gains can come from a variety of creative sources.

The Billet 5 X 5 Hub is shown with the rotor flange and the T-Nuts (Gold) installed to "float" the rotor. The T-Nuts fit solidly in channels for firm braking, but can move slightly left and right adapting to changes that occur due to heat expansion.

Anytime you have found a reduction in resistance – you can go to your favorite safe (safety is first, second and last) hill and let the car roll. If you have recorded your start and stop points you can visually see if you have found resistance savings that allow the car to roll further down the same hill keeping variables as close as possible. Gravity and the same starting line is all you need. Make sure you use the same tire widths and air pressure. Even stagger needs to be maintained to keep your coast down measurements relative.

This rotor flange and cast hub can be bolted solidly or T-Nuts can be added at anytime as the rotor flange accepts both direct mounting of a floating set up. 

 A great way to make your car coast further is to use a floating rotor set up. Floating your rotor with T-Nuts gains 6 to 8 coast down horsepower. T-Nuts reduce resistance and improve braking force. T-Nuts promote even pad wear and make your brake system more efficient. Even wear and rotor that adapts to movement and creates better pad contact under braking. The same action frees up the rotor allowing the car to roll freely with less drag between the rotor and the pads.

T-Nuts allow for side to side movement of the rotor to reduce pad drag and reduce heat transfer from the rotor into your shocks. T-Nuts fit solidly in rectangular channels controlling rotational force for rock solid braking. The Left to Right movement of the T-Nuts compensates for heat expansion and negates the effect of slight caliper misalignment. 

 Floating allows the rotors to move laterally, but maintains solid stopping power in rotation. The T-Nuts fit in tight tolerance channels providing a solid connection to apply stopping force from the caliper, through the rotor and ultimately to the tire contact patch. The same T-Nuts allow the rotor to move slightly left and/or right. The movement reduces drag friction on the pads. The floating action cancels out any slight misalignment in the caliper mounting and washes out friction from rotor warping to some degree. The T-Nuts allow the rotor to run true through the center of the pads in a parallel fashion.

As an added benefit, the aluminum rotor flange dissipates heat allowing your braking system to run cooler. The T-Nuts are floating so the indirect contact with the rotor flange transfers less heat from the caliper and insulates that same heat from transferring into the hub. Reduced heat transfer helps your parts to perform and last longer.

This rotor flange can be bolted solidly or can be used with T-Nuts for a floating rotor set up. The bolt on rotor flange helps to dissipate brake heat. Used in conjunction with T-Nuts, heat transfer created at the rotor is reduced due to the T-Nuts "floating" in the rotor flange which interrupts the heat path for superior performance.

NASCAR teams often use the “coast down” hill test and let gravity be the constant that allows for solid repeat testing. Cup teams also use chassis dyno’s so they can measure the horsepower that actually makes it to the ground. My sources tell me that they have witnessed floating rotors add 6 to 8 horsepower on the chassis dyno as compared to running solid rotors.  Making 6 horsepower or so due to brake efficiently is a nice gain and you get the added benefit of parts that last longer due to lower operating temperatures.  

The HP gain is due to the floating rotors finding center through out the heat expansion range so rotor rubbing on the pads when your foot is off the pedal results in less friction. The T-nut set up and rotor flange allows for a bit of movement that absorbs rotor warping and isolates the rotor from the hub resulting in less brake pad drag. You get the horsepower gain and the brakes run cooler due to less pad and rotor contact. Drivers report smoother braking with reduced pulsing adding to the efficiency of the braking system.

Additional coast down gain can be found by adding low friction hub seals. Low friction seals pick up a few more horsepower. The low friction seals do come at a higher cost, but if you use hubs with a seal retainer system you can re-use those expensive seals again and again. Standard hubs require seals to be a onetime use item so low friction seals need to be considered alongside the budget available to your team.

Low Friction Seals reduce rolling resistance, but can cost about 4 times as much as standard seals. The low friction seals increase Coast Down Horse Power and is a good idea if you budget can afford the added expense. Using hubs with a Seal Retainer System allows you to re-use expensive seals over and over again helping to offset the added expense. 

Coast down horsepower is a phrase that should be ingrained in the minds of race teams. Any idea that makes your car coast downhill with less effort should be considered. T-Nuts are a mechanical example, but low friction bearing seals and hub friction are other areas of great gain. Aerodynamic changes can result in benefits as well.

Several past tech articles that can be found in the JOES Knowledge Center touch on other areas where rolling resistance can be reduced via mechanical or aerodynamic improvements. The goal is to keep your team thinking of every advantage to get efficient application available energy resulting in increased speed. More speed involves pushing on ingenuity. Ingenuity builds exponential momentum that will push new ideas down the hill of continuous improvement.

Go Forward – Move Ahead

Jeff Butcher

01/29/13

Why Anti Dive?

Conceptually, Anti Dive is not really a difficult geometric program to understand. Engineers find a way to overcomplicate what is simple. Hey, we need engineers, but our chassis builders build in only so much adjustment for Anti Dive so we really can’t get in too much trouble if we have a basic understanding of the mechanics involved. On a stock car, that has upper A-Arms and lower control arms (like the cars that you see in this magazine), it pays to simplify Anti Dive to the point of practicality. On a stock car, we can only take the adjustment to certain limitations so we can focus within the relative boundaries that a typical stock car situation presents.

Your car brand of car has the Anti Dive pre-set to match the philosophy of your chassis builder Still, all car builders give you a multitude of adjustments. With care, adjusting Anti Dive can be the fine tuning tool that helps you overcome a chassis problem, which in turn starts a positive domino effect that results in more speed.

Before you start playing around with Anti Dive as an adjustment, it does help if you know what it is? Randomly moving things falls in the luck category. While random adjustments are less than desirable, over thinking is equally as dangerous. Your car is built with limitations so the Anti Dive adjustments that fall in the practical category are pretty easy. Unless you get out a cutting torch – you can adjust way as if you are moving the panhard bar up and down. Just do it – and then undo it if the driver doesn’t like it. Keep it simple certainly applies.

So just what is Anti Dive? From the side view of your front suspension you have pivot points for the upper A-Arm and pivot points for the lower control arm. These pivots and their relative location to each other create Anti Dive. Anti Dive can be different on the LF and the RF. Manipulating Anti Dive differential at the LF and RF can be an adjustment that you can use to your advantage. Anti Dive is the common term, but we can use Pro Dive as part of the adjustment option set?

To visualize, have a look at your right front suspension. In general, the upper A-Arm pivots are parallel to the frame. If you look at the connection points at the bottom and visualize those as parallel to the frame you have zero Anti Dive. Now, maintain the visual of the bottom pivots being parallel to the frame – then move the back of the RF Arm down ½”. You just put Anti Dive in the Car. In this example, if you were to lower the front of the RF A-Arm pivot, from parallel, you would put Pro-Dive into the suspension. The same holds true on the Left side.

In this photo you can see that the RF A-Arm is nearly parallel to the frame. If you look at the lower pivot points they are parallel as well. Raising the front of the RF A-Arm, so that the front pivot is higher off the frame (ground) than the rear pivot, creates a an A-Arm arrangement that is identified as Anti Dive.

So, lowering the back of your A-Arms puts Anti Dive in the car – it’s an easy adjustment that you can make right at the track. You can adjust Anti Dive with the lower control arms, but for this article we are focusing on the upper A-Arms so that the concept is the focus. Hopefully, concentrating on the upper A-Arms reduces confusion in our quest to promote a new possibility. The goal is to get you to think out the information so you can see if you want to add adjusting the Anti dive to your adjustment arsenal this week.

This view again shows the A-Arm parallel to the frame, which creates zero percent Anti Dive. you can adjust the Anti Dive with the lower pivots, but for this article we are focusing on the Upper A-Arms so that proving the concept is the focus. The concept is simple, but by taking the lower points out of the equation, for now, confusion is reduced and your understanding of Anti Dive will allow you to understand the adjustment. Once the engineering is understood - you will find that using the lowers to adjust Anti Dive has a dramatic affect and a little goes a long way. The Billet Nut Plate is a cool option that keeps your hands away from hot headers.

If the Upper pivots are parallel to the frame and the lower pivots are parallel to the frame then you have zero percent Anti Dive. You can adjust until you have 100% Anti dive and when the brakes are applied the front end will effectively be locked up and the suspension will not drop at all. The Anti Dive will carry the weight of the car based on the transfer from the rear coupled with the weight transfer affiliation of the Center of Gravity of the car – so there is the science. How about we just slap in some slugs and remove the complicated engineering speak?

Using A-Arm frame mounts with slots allows for the use of slugs making track side adjustments quick and easy. Slugs allow you to make adjustments in 1/8” (or smaller) increments and the solid mount ensures you can repeat adjustments with easy documentation. You can make a change and if the driver likes it then great – if not, a quick slug replacement gets you right back to your baseline. You can save the heavy math and engineering for when you have graph paper and a lot of time at the shop. At the track – simply slap in a slug to make a 1/8” to ½” adjustment at the upper A-Arm pivot and you have plenty of adjustment for Anti Dive or Pro Dive right at the track. You can make the change in 5 minutes and the slug system gives you hardware that is recordable and repeatable. Good science always comes with repeatability.

If you look closely, you will see a slug at the rear pivot of the Upper A-arm. The slug raises the back of the A-Arm as the offset is larger than the front. The slug combination raises the back of the A-Arm and this angle creates Pro Dive. A simple slug adjustment allows you to quickly change the amount of Pro or Anti Dive right at the track. Typically, slugs are made in 1/8" increments so you can run Pro Dive as shown in the photo to help set your car into the turns. The slugs give you a solid mounting system that is secure and recordable.

Now that you see how easy it is to move the A-Arm mounting slug hardware – why should you run Anti Dive? Or, why run Pro Dive? When it comes to racecar suspensions, everything is about timing. Anti Dive is creates mechanical resistance under braking. The percentage of Anti Dive can be drawn out on paper easily in the shop - at the track just toss in the different slugs to accomplish your goals. Under braking, Anti Dive resists the dropping movement at the front end under braking. With the mechanical resistance created by running Anti Dive, you can potentially run softer springs and the Anti Dive will carry you through the braking zone. When you get to the middle and lift off the brakes, the soft springs can allow the car to roll or drop as Anti-Dive is reduced to nearly zero when you are not loading the suspension with brake torque. Remember, the Anti Dive resistance occurs under braking so a bumpy track can potentially cause trouble – Anti Dive works best on smooth tracks.  Well, I think it works best on smooth tracks and you will find that crew chiefs have varying opinions on this issue.

To help with the mental picture – if you have your RF A-Arm parallel to the frame, then the A-Arm is free to move up and down without any friction or mechanical resistance. If you were to exaggerate the adjustment and place the A-Arm so that the pivots were 90 degrees to the frame, instead of parallel, then you can see the suspension would be locked and could not move. Since practicality only lets us move the A-Arm pivot about ½” up or down, in comparison to the other mounting hole on your A-Arm, you can see that the braking force resists movement based on the amount of adjustment that your slotted A-Arm ear allows for. Again, you can get more adjustment on the bottom if you need it, but we are focused on the top for simplicity of proving the concept.

Running a slotted A-Arm frame ear on your car allows you to use pre-measured slugs that mate perfectly  for a secure mounting system. Slugs that are engraved with the offset give you an easy reference so your team can record Anti Dive or Pro Dive adjustments in your set up book. Half inch slugs installed in the front of the ear and at the back of the ear give you a full inch of adjustment in a 6" space. For most purposes, the percentage of Anti Dive achieved with the use of (2) opposing 1/2" slugs is a large adjustment. With Anti Dive - a little goes a long way.

By now, hopefully you have an idea of Anti Dive, but what about Pro Dive? When would you want Pro Dive? If Anti Dive resists the nose dropping under braking then Pro Dive (when the front of the A-Arm pivot is lower than the rear  of the A-Arm pivot) helps the nose to drop under braking. On a street car, Anti Dive is put in the right and left side to create braking stability. The same amount is run on both sides.

For racing, running Pro-Dive on the LF with Anti-Dive on the RF can help pull the car into the turn. In effect, the car gets some automatic steering under braking promoting a good set at corner entry. You can experiment with running Anti Dive on both sides, or running Anti Dive on the RF and a bit of Pro Dive on the LF. Simple slug changes allow you to see what works best at your track and with your driver.

Slugs that mate with A-Arm ears are marked allowing for the ultimate in adjustment and repeatability. Simply record the slug numbers and your set up book will contain an easy reference to repeat adjustments. 

Considerations that come into play are the amount of braking force – if the track calls for heavy braking then the Anti Dive or Pro Dive is going to be accentuated by the full on brake force. If the track allows for smooth braking then maybe you can run more Anti Dive to accomplish your goal. In general, Anti Dive can help give the car stability at corner entry under braking – when the brakes are released your soft springs can ride over the bumps and roll easily into the turn. Running Anti Dive might allow you to run the soft springs that help in the middle or over bumps as the mechanical resistance created by Anti Dive carries you over the braking portion of the track.

Pro Dive on the LF might help set you into the turn – maybe you will be able to run a little less stagger by using a small amount of Pro Dive at the LF. Potentially, less stagger will keep your car hook up on corner exit? The trick is to mix the amount of Pro Dive on the LF with Anti Dive on the RF to help you overcome a problem without changing a spring that could hurt the car later in the turn. Maybe, the Pro-Dive in this scenario starts the dominos in the right direction allowing you to run less stagger?

You can also measure Anti Dive by using an accurate level to record the A-Arm angle in degrees. An accurate Digital Level will give you a number that you can record in seconds. 

The same holds true for bite, stagger and all of the adjustments at your disposal. If you think out the when and where, Anti Dive can help you to fix a spot in the corner that is giving you trouble you can potentially use Anti Dive or Pro Dive to your advantage. While running Anti Dive is common place, Pro Dive can be a good place to experiment. It is standard to run Anti Dive on both front corners. It is very common to run Anti Dive on the RF with Pro Dive on the LF. All that said – there is no rule that says that Pro-Dive can’t be bolted into both front corners – just be careful that the car is stable under braking. All of my articles hammer on the concept that a car that is unstable at corner entry must be fixed or it is going to be a long night. I never risk a set up that has any possibility of being loose on corner entry – period.

By realizing that Anti-Dive resists movement under braking, and Pro-Dive promotes movement under braking, your team can overcome obstacles with another adjustment mechanism in your chassis set up tool box. Small changes go a long way. Using slugs allows you to make changes 1/8” at a time. 1/8” may not sound like much, but it is 1/8” on a 6” bolt pattern so the degree change is significant. Using a ½” slug turned up on the front of the RF A-Arm and a ½” slug turned down on the back of the RF A-Arm provides you with a ton of degrees of adjustment. I just write down the slugs dimensions – you can measure degrees with a digital level in about 3 seconds – keeping the article understandable is my goal.

The limitation is not in the hardware, but rather in your need to truly need Anti Dive or Pro Dive to fix a real problem. Just because you can adjust the Anti/Pro Dive doesn’t mean you should. In this case, a little goes a long way and under doing it is better than going overboard. Still – top teams adjust the A-Arm angle with the same mental ease as changing stagger or Panhard bars. Experiment and maybe you will learn a new speed secret for your particular car and track. Or, by understanding the adjustment – you can ensure that your car is assembled properly and the Anti/Pro Dive is set within parameters that your car builder had in mind. Measure, experiment, document and repeat – that sound pretty scientific to me.

Go Forward – Move Ahead.

Jeff Butcher

08/01/12

Brake Balance Adjustment

Balanced stopping is as important as a balanced set up. To win, you need all 4 calipers doing their share of the work. Ensuring that your braking system shares the load proportionately will create a fast and stable car on corner entry. Your brake manufacturer can utilize past experience to help your team to select the correct components for your car weight, tires, horsepower, track size and banking. When I was young, my Dad taught me that 4 tires work better than 3 when it came to chassis set ups. The same holds true for braking. Getting all the tires to share the load results in faster lap times and improves consistency.

Once you have installed the correct brake system components, a brake balance bar is one of the few adjustment tools the driver can utilize right from the seat. For your brake balance bar adjuster to work properly, it is vital that you set up your pedal balance bar per the instructions provided with the hardware. For trouble free operation the pedal balance bar must be parallel to the frame rails when the pedal is full depressed. Often, teams set the balance bar parallel to the frame in the static position – this will cause binding and problematic performance. Installing the pedal balance bar parallel to the frame in the depressed position allows the front brakes to come on first promoting a stable corner entry.

After you have verified that your parts are installed correctly, you can begin choosing a brake balance bar adjuster that meets your needs. A quality brake balance cockpit adjuster will give your driver a tool that can be used during racing action.

This Brake Balance Adjuster is lightweight and mounts without dis-assembly. The steel braided flex hose is reinforced with Nylon tubing on the interior nearly eliminating the chance of binding.

Understanding how the brake balance performs will help you to get the most out of your brakes and your driver accessible adjustments. By cranking on the adjuster you are changing the percentage of leverage force to each master cylinder. Adding front brake changes the angle of the pedal balance bar assembly. In a given amount of pedal travel – adding front brake reduces the travel distance of the rear master cylinder piston. Reduced travel equal less total braking force.

Adjusting the brakes with a brake balance bar comes with compromise. Today’s brake systems are very advanced. The small reduction in overall braking force is often a good trade off as gaining the adjustment ability can be the difference between winning and losing. At tracks that work the brake system to extremes, it is important to consider that overall braking force is reduced. If you run at the same track every week you may want to explore different brake components verses relying on the adjustment method. If you find yourself dialing to all front or all rear every week then replacing components may be a choice that allows your brake balance adjuster to be more effective.

Changing the leverage percentage to favor the front brakes promotes a solid corner entry. Getting your car into the corner in a stable fashion is mandatory for drivability and builds driving comfort. If you go too far with the front percentage then your car can exert too much force to the front tires and the car can begin to pick up the dreaded middle push. Adding front braking percentage is a great choice if the car is twitchy or uncomfortable at corner entry.

Conversely, if your car has a pushing condition then dialing more rear brake can help to set the car into the turn via the rear brake assist. More rear brake percentage can be a great tool that helps a car to turn. Use caution as going too far can create rear brake lock up should the driver need to smash the brakes to avoid an accident.

Caliper mounted Brake Pressure Gauges allow you to check the pressure at each caliper. Regular use can help you to identify brake system issues. If you see a reading that is outside your norm you should inspect your brake system to find the root of the problem

At tracks that create bright red glowing rotors your goal should be to work towards having the rear brakes do as much of the stopping work as possible. Identifying the point where too much rear brake causes unstable corner entry provides a record of the setting to avoid. Once the maximum rear brake bias leverage point is established a few turns to the front for stability will help to minimize the potential for an unstable entry. Achieving the maximum from the rear brakes takes load off the front. At heavy braking tracks, obtaining maximum safe force out of the rear calipers can prevent overworking the front brakes.

There are many brake balance bar adjuster systems on the market. Be sure to mount your version properly. Utilizing a robust flex connecter at your pedal assembly prevents unwanted binding. Steel braided versions have a rigid Teflon interior that resists binding – a guide support and a straight shot into the pedal assembly promote smooth operation.

 If your brake balance adjuster system is a speedometer cable style, be sure to have a straight connection point and provide a cable guide support near the pedal assembly. Speedometer cable style units can flip into a loop rendering your adjuster useless at exactly the wrong time. Proper installation will prevent the cable from flipping into a knot. The rubberlike coating on the speedometer style cable can melt with heat. Often, the melting happens with a new car when the rubber cable sleeve is strapped to close to sources of heat. Route away from heat sources or insulate the rubberlike coated cable versions to prevent the outer coating from melting onto the cable.

Driver brake adjustment, used properly, can be the final touch to get the last ounce of speed from a good handling racecar. Further, cockpit brake adjustment can help drivers to adjust to changing track conditions or wearing tires.

Gain can come with pain. Over use of the brake adjuster can cause teams to chase their car handling characteristics. If you think of the brake balance adjuster as a fine tuning tool you will rely on chassis adjustments to balance corner handling – keeping the balance adjuster in the center of the range when the green flag drops provides the maximum adjustment ability during the race. Starting the race with the pedal balance bar perfectly parallel to the frame in the depressed position puts your brake system in the center of the range and provides maximum braking force.

Brake Balance Adjusters with a measuring scale make recording your setting an easy task. You should record your brake balance setting as a routine part of your set up process.

Recording your brake balance adjustment should be a weekly routine. You can measure the setting with a cockpit adjuster system that utilizes a scale to indicate balance position. Another option is to track the amount of turns front or rear “off of center”. If you count turns you simply record the number of adjustment turns with center being the pedal balance bar being parallel to the frame when depressed. For more accuracy, you can use calipers to measure the pedal balance bar location by measuring the master cylinder rods before and after each race.

Dash mounted Brake Pressure Gauges give you a quick reference to witness the line pressure difference created with just one turn on the Brake Balance Adjuster. Dash mounted gauges can give you an early warning to braking system leaks or problems.

You can utilize brake bias pressure gauges to witness the affect of turning the brake balance adjuster. Just one turn can make a significant change on the bias gauges. Understanding your bias gauge readings can help you to establish a baseline for your brake set up. Keep in mind, that pressure is just one element in your braking system. Variables such as piston size, quantity and master cylinder size must be taken into consideration. A brake bias gauge set provides an easily viewable baseline helping you to leave the shop ready to go – or should I say stop?

As with any adjustment, it is only good if you can repeat the change in a consistent and predictable fashion. With the proper hardware, your team can eliminate problems and orchestrate a bias towards winning.

Go Forward – Move Ahead

Jeff Butcher

04/1/12

Instant Center Adjustment

Why do we care about the Instant Center in the front suspension? We know our car builder spent plenty of time engineering the proper roll center. Instant Center of the Left and Right side front suspension are a piece in the puzzle that creates Roll Center.

Since I am opposed to over engineering at the track, I prefer to focus on Instant Centers and adjust them with the same freedom that is applied to adjusting the rear roll center. “Just try it” is my philosophy when it comes to adjusting the Instant Center at the track.

Before you start moving parts around it does pay to understand the geometry that creates instant centers. I like to explain mechanical design by using words like “stuff” or “things” instead of complicating simple topics with big phrases such as “dynamic roll propagated via G-Force induced dynamic wheel loading”. Really, we can explain stuff by simply understanding that there is more front end travel at a high speed high banked track than you would find if you set up some orange cones in a parking lot.

Timing your suspension travel by balancing spring rate, roll bars and shocks with the leverage created by Instant Centers can maximize your Big Bar set up. For that matter - any set up is benefited by experimenting with Instant Center locations.

Instant Centers are easy to visualize. You find the little spot the same way on both sides of the front of the car. For this review we will take a snap shot of the RF suspension. Your A-Arm is bolted to the frame via an ear that is welded to the frame horn. Your lower control arm bolts onto the cross member. You have a spindle pin and the tire size sets the height of the wheel center off the ground. Your A-Arm is about 7” to 12” long and your lower control arm is probably around 16” to 18” long for your typical late model that has a 63.0” track width. Basically, if you have a stock car, the parts that create the Instant Center are similar regardless of your brand of car.

My goal is here is to eliminate the fear that can be associated with the big pile of details that create the magical Roll Center. Really, roll center is often found at about 1.5” off the ground to 2.5” off the ground for most cars – give or take an inch. The left to right location moves all over the place depending A-Arm length. Of course, as soon as you run the suspension through travel the roll center moves about. With a huge roll bar, the rules have changed and once the car has been pulled down to the ground with your insanely stiff rebound shocks, the roll center and instant centers move around much less as compared to when we had a pair of 350’s on the coilovers and an 1-1/8” bar.

Big Bars require new thinking. Since planting the nose piece to the ground is the new norm, then it would seem that the suspension layout is less important – or is it? With the nose piece held to the ground by huge rebound numbers and a sway bar that nearly eliminates body roll, then why do we care about roll centers and instant centers at all?

While the movements are less, they are still there. We still have dive, roll and plenty of bumps. But, all of those movements happen faster and the distance traveled, once the nose pieces is sucked down, is less. With this “new” information how can we make an effective adjustment utilizing Instant Centers along with shocks and springs?

It pays to think about the mechanical leverage of the Instant Center. Adjusting the Instant Center can be the subtle adjustment that compensates for the reduced actual center of the corner travel induced by giant sway bars. Since the Instant Center is 2 simple lines per side we can visualize it easily. The first line is drawn through the center of the upper ball joint and extending through the inner pivot. Be sure to find the true center of the ball joint provided by your ball joint manufacturer. The second line extends from the lower ball joint through the inner pivot on the lower control arm. Extend both lines until they intersect. Boom – the Instant Center is created. Through suspension travel the intersect point moves based on the length, angle and connection point of the upper A-Arm and the lower control arm. See the accompanying photo for the visual and you will see that Instant Centers are pretty simple to understand.

The Instant Center is easy to visualize right at the track. Simply follow the lines of the upper and lower arms until they meet. Be sure to utilize the actual ball joint center provided by your ball joint manufacturer.

Now examine the RF Instant Center and how we can use mechanical leverage to our advantage. Let’s assume our track width is 63.0”.  If the hypothetical RF Instant Center is 4 inches off the ground and 3 feet left of the vehicle centerline we end up with about 49.5” (close enough) of leverage. If we make the RF A-Arm Longer and keep the same connection point on the frame ear pivot we move the RF Instant Center more to the left. The longer A-Arm gets flatter and it takes the imaginary line longer to run into the line from the lower control arm. The change lowers the RF Instant Center as well. So, hypothetically, let say we moved the RF Instant Center to left about a foot and down 2” (Since we are starting from a known baseline all we care about is the direction of the adjustment – we can repeat the change by tracking the slugs we use).

 A-Arm length and mounting height have a dramatic effect on Instant Center Location. Carrying an inventory of A-Arm lengths gives you more Instant Center Adjustment choices right at the track.

The longer lever arm created by the adjustment scenario in the prior paragraph compresses the RF spring more than it would have in our baseline set up. The car speed and banking provide the same amount of force, but the longer lever creates more travel at the RF. Really – it is like running a softer RF spring when the chassis rolls. Lowering the RF Instant Center promotes more roll. The longer lever from the Center of Gravity gives an additional boost to roll.

Bolt on tube sections make quick work out of changing A-arm length. Moving Instant Centers at the track is an adjustment you should try more often. The bolt on tube section is a rigid advantage on snouts where the A-Arm wraps around the frame.

Here is where the fun starts – let’s keep it simple. You can draw your suspension and do the actual math and record it for future reference. For now – let’s just think about the concept. Moving the RF Instant Center to the Left effectively softens the RF spring through chassis roll. But, if you want a softer RF spring, why not just put one in? Well, this is where you need to think about the corner entry, when the car is relatively traveling in a straight line, and the corner middle where the car is in full roll. If you balance the Instant Centers, and consider all of the compromises that come with race car set ups, you can make subtle adjustments by manipulating the timing of suspension compression (corner entry) and suspension roll (corner middle).

When your car is going perfectly straight, the giant sway bar is doing about zero. If the car is going straight and you smash the brakes then the ultra soft springs you have up there may not hold the car for a stable entry. You can fix the problem by adding stiffer springs for straight line (entry) braking, but then the middle may suffer due to the stiffer springs you thought you needed? From your baseline, adding front spring to get some help with corner entry stability coupled with moving Instant Center to the left creates a lever to help the car roll – now you get help under braking without suffering more spring rate during roll. The game is in balancing the Instant Center with the entry “dive” and the mid-corner “roll”.

Your car builder has the baseline figured out when it comes to Instant Center and Roll Center. But, track conditions change and driver styles vary. Maybe you can utilize Instant Center changes just like you use the Panhard bar? Try it and see if “Mikey likes it”.

The adjustment idea I like best for Instant Center manipulation is to use the same length A-Arm but simply move the upper frame pivot point up and down to get your desired result. I prefer moving the pivot point of the upper A-Arm for subtle adjustments. The benefit of moving the upper pivot point is that hardware is available to make it easy, you can make subtle changes, you avoid messing up the bump steer and the camber curves stay in line. Your car builder spent a mountain of time and testing on your baseline front end design so it pays to make adjustments that are subtle verses stretching the design parameters to extremes.

Using a slotted ear and slugs makes adjustments easy. You can move the pivot point in small increments by carrying a slug kit. You can raise and lower the Instant Center right at the track. If you want more roll, but don’t feel like you can run softer springs, you can simply change a slug and raise the RF A-Arm Pivot point. Raising the pivot point will move the RF Instant Center farther left and lower. The subtle adjustment gives you some turning help without decreasing braking stability. The RF gives you easy adjustment and you can “feel” the affect of the change just like when you move the panhard bar. You do have to readjust camber – easy deal.

Slugs that are marked give you an easy way to record Instant Center changes. A 1/4" slug makes a profound difference. Draw it out when you have time. At the track, just bolt in a pair!

A slotted A-Arm frame tab works perfectly with the slug system allowing for quick and precise adjustments.

The LF Instant Center is important too. You can use the LF to raise or lower the roll center. You can also use the LF to move the roll center left or right. You can accomplish the same thing with the RF, but this article is trying to provide simple examples to help your team see the concept and give you the confidence to try what may be a new adjustment for your team. You can certainly draw it all out, but for today just think about what happens when you move the Instant Center with simple A-Arm slugs.

When you run a Shorter RF A-Arm you generally move the roll center to the right. The shorter RF A-Arm has more angle and intersects with the lower control arm line faster – that is easy to understand, right? If the Roll Center is closer to the right it speeds the rate of travel and the car reacts quicker. Go too far and you will blast through the travel before the full force of the center of the corner arrives. When this situation occurs, the “soft push” is usually the result. So, this is a magazine article and you have a race car going around a real track. Reading is fun and accepting the limitations within this article will help you to just try adjustments. There are a ton of variables and the goal of this lesson is to simply discuss one element as if Instant Centers were not connected to anything else – of course they are! But, if by forgetting about all of the other “stuff” we can learn how to manipulate Instant Center adjustments to overcome a problem then we have learned something new.

Changing A-Arm length requires the camber to be reset. A billet nut plate speeds changes when time is short. An accurate billet caster camber gauge is a must for any race team.

Since your car builder spent the time to build your car with a proven Roll Center location we want to be careful to not adjust so much that we erase the years of testing and knowledge that our car gives you when you buy a frame. So, from a prior article Roll Center is explained here:

Roll Center Explained:

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 lower outer ball joint center though the lower control arm frame pivot. The RF lower control arm line is extended out until it meets the RF upper control arm line. Where these lines intersect is called the Instant Center. The LF Instant Center is found in the same way.

After both 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, running from the contact patches to the corresponding Instant Center intersect, is the Roll Center. Remember – the Roll Center moves as the suspension goes through travel.

Spend time to learn about Roll Center when you are in the shop. At the track - trial and error is still common, even for Cup teams with full time engineers. 

Note:

Since the “Roll Center” location is a moving point is space it gets complicated – carrying graph paper at the track is not feasible, I prefer to spend time thinking about roll center during the design stage of building a chassis – and much thought is placed into Roll Center when designing any suspension.

 At the track, it is easy to visualize Instant Centers and difficult to think out roll center. By simplifying, I can adjust Instant Center locations right at the track as I can easily see how the upper A-Arm line passes through the lower control arm line. With simple visual estimation, I can have another adjustment method at the track and I carry slugs to make repeatable changes just like I would move the Panhard bar or change a spring.

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. For the Front Instant Center adjustment you can simply record that you moved the RF inner A-arm mounting point up a1/8th inch with a slug. Changing a slug is pretty easy.  If the driver doesn’t like the adjustment you can simply bolt the original slug back in.

Instant Center adjustments at the track can be used to create the feel of stiffer front springs under braking yet have the front springs feel softer in the center of the turn due to the longer lever that is created by the Instant Center length change. Many variables come into play and the teams that get the variables closest wins.

At the track – I usually focus on Instant Center adjustments by moving slugs on the upper A-Arms. You can move the lower points too, but you bring in rack location issues and bump steer corrections. The upper adjustment is easy to understand especially when track time is limited.

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.

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? Keep it simple at the track and use slugs to maintain records and repeatability. You can engineer at will after the race and study the Roll Center changes you accomplished and measure the affects of bolting in a few simple slugs.

Engineering becomes more important in racing every day. When time is short, educated experimenting is equally as valuable.

Go Forward – Move Ahead

Jeff Butcher

06/08/12