Nice Rear End

Nice Rear End

Getting to the front often start with a good rear end. Today, there are many options and choosing the right rear end type for your team is the goal.

To help your team choose the correct rear end type for your car, I interviewed Frank Loverock of Quick Change Exchange. Frank manufactures ratcheting rear ends and differentiating rear ends and he has provided a wealth of information for this article. In addition, Randy Larsen of DPI added thoughts relating to the benefits of differentiating rear ends as well as his thoughts on the different styles of rear ends and other tips.

Rear Ends – A simple overview

A spool is a simple chunk of billet aluminum with axle splines. The spool is very durable and simple. Since the axles are solidly connected, a spool requires stagger to deal with the LR tire following the shorter radius at the inside of the corner as compared to the RR. When you push a car through the pits you see the LR tire skip as it catches up with the larger radius of the RR tire.

The Locker (Ratchet) allows the wheels to unhook one tooth at a time on corner entry. The “ratcheting” mechanics allow the LR to roll in the corner in conjunction with the RR helping to overcome the negative effects of stagger on corner entry. As soon as any amount of throttle pressure is applied, the locker (ratchet) locks up and performs like a spool. Both axles are locked together and when the power is put down a ratchet and a spool work the same.

Differentials utilize a series of gears that apply the power to each rear tire individually. Less stagger is required and if your stagger changes the differentiating action works to keep the handling characteristics of your car the same throughout the race. A differentiating rear end has moving parts that require regular maintenance. Quality gear oil is needed and performance can be changed based on the type of oil used. Coolers are highly reccomended when you run a differential style rear end unit.

Differentials apply power to each wheel independently and the need for stagger is reduced. The axles are not solidly connected together and internal gears apply power to each tire separately. The result is a rear end that compensates for stagger changes. The car is more consistent and self adjusts for changing corner conditions.

Racing differentials feature an aluminum housing for lightweight. Manufactures are always discovering new ways to improve performance while producing lighter weight parts. Unit's of today do more and weigh less due to design improvements and superior machining techniques.

Q & A

As compared to a spool – why is a locker a good choice?

Frank Loverock:

The benefit of a locker is improved corner entry. As you roll into the corner, without any throttle pressure, the car enters the corner and the effects of stagger are basically eliminated. Both tires roll in equally as specially designed springs control the ratcheting action. At entry, the LR is connected to the driveline and the right wheel ratchets forward creating an entry without effective stagger. The car never freewheels, either one or both rear tires are connected to the driveline. The instant you push the throttle the ratchet locks up and you drive both rear tires 100% just like a spool. A locker (ratchet) is a spool 90% of the time so it is a myth that you can run less stagger.

Randy Larsen:

A locker can help a car into the turn and reduce an entry push. The rear tires ratchet in a controlled fashion for a more stable entry. Since LR isn’t dragging entering the turn, drivers can drive in deeper. A locker becomes a spool as soon as the driver hits the gas so stagger settings are critical. Under power, the locker acts just like a spool so your tire guy needs to make sure that the stagger remains perfect throughout the race. Any change in stagger is going to be felt and loss of stagger often will create a nasty center push.

As compared to a spool – why is a differentiating rear end a good choice?

Frank Loverock:

On a circle track car, the RR must travel faster and further than the LR due to the larger corner arc on the outside of the track as compared to the inside. The differentiating action turns the LR at a slower rate helping the car to turn.

Differentiating rear ends offer great advantages but come with significant maintenance so a trade off is made. The benefit is a car that really turns. The rear end may drive the LR 49% and the RR 51% and the unit is always differentiating applying power as needed to the wheel that needs it most. Differentials never drive the LR and RR equally but rather compensate for the ever changing position on the track. In other words, differentials are always driving the appropriate wheel faster than the other eliminating the dragging of a tire down the straight away. The faster turning of the outside wheel gets your car through the center with less dependence on stagger. Spools and lockers drag one tire if you are running even a small amount of stagger.

Randy Larsen:

A differential gets you through the center allowing the car to turn freely setting you up for a straight and powerful exit launch. The differential action allows you to run the low groove one lap and the high groove the next as the gear mechanism compensates for the change in corner radius. If your stagger changes - the differential will make up the difference so you car stays fast the entire race.

Since the differential gets you through the center, you can adjust your set up for a tight launch off the turn. The differential gives you more chassis set up options than a standard spool and the driver feel through the center is vastly improved. When your stagger changes a spool driven set up is negatively affected. The torque sensing action of differential units allows the car to roll freely through the center and compensates for changing stagger.

What improvements in design and quality have been added to rear ends?

Frank Loverock:

Superior machining operations create parts that mate together precisely for smooth long lasting operation. Better materials coupled with sophisticated heat treating processes create unparalleled longevity and performance. Rear end units last longer and work better through exploitation of modern science. Knowledge from the past is applied to what we build today. Historical influence is partnered with advanced modern day processes creating improved product at fair pricing.

Randy Larsen:

In racing, heat is nearly always the enemy. New manufacturing processes have allowed components to be light where needed and designers can pinpoint the need for mass at critical areas. Heat treating and CAD software have allowed differentiating rear ends to be optimized as compared to past designs. The optimization results in consistency. Units manufactured today limit and compensate for heat expansion efficiently resulting in enhanced performance.

What rear end types do you recommend to experienced racers?

Frank Loverock:

For experienced teams, a locker or a differentiating rear end is a good choice. It comes down to driver feel. Experienced teams are better suited to handle the added maintenance and often have larger budgets. The benefits of advanced rear ends, provides choices for experienced chassis gurus. With better feel, drivers can often get more speed by utilizing a rear end that matches their style, track and set up.

Close tolerance machining processes allow rear end units to do more at lower temperatures and with more longevity.

What rear end types do you recommend for beginning racers?

Frank Loverock:

For beginning racers I think a spool or maybe a locker is best. It all depends what the new driver wants to get out of their career. If they hope to move up to the top NASCAR divisions then gaining a feel for a locker becomes more important. All the top NASCAR series require lockers so gaining experience is a factor. Lockers require maintenance but the rebuild cost and time is manageable.

I strongly believe that a beginner should keep things simple so the spool is a good choice. As beginners gain experience and understanding grows, then experimenting will help their learning curve. Trying new things will help beginning teams to learn what different adjustments can accomplish. Starting from a simple proven baseline speeds the learning curve. As knowledge increases and drivers become more confident, then replacing the spool with a locker or differential creates a situation where teams can learn and feel the benefits from trying out new ideas.

Coolers, Oil & Maintenance for lockers and differentials?

Frank Loverock:

A rear end cooler is highly recommended and the best quality gear oils add to performance. Our group has designed synthetic oils that are specifically engineered for the friction created by the differentiating action. The test time to create exceptional gear oil is unbelievable and regardless of the gear oil you choose, quality is a must.

Randy Larsen:

Gear oil choice for differentiating rear ends is an area where spending more is always the best choice. Inexpensive gear oils translate to worn out hardware. We recommend top quality gear oil such as Joe Gibbs. We recommend coolers as reducing heat increases longevity and consistency.

Both Frank and Randy recommend servicing Lockers and differentials twice a year based on 25 races under 100 laps. A once a year rebuild “can” be okay. But, stretching service intervals can result in diminished performance. Personally, I would go with twice a year, as a minimum, based on the 25-100 lap race schedule. A locker requires less maintenance as compared to a differential. Ensuring that locker springs hold their designed rate is a must.

How has the use of rear end units changed?

Frank Loverock:

Experience has allowed us to manufacture 6 different springs’ rates for locker units. Stronger spring rates give the car a tighter feeling on corner entry. Lesser rates free the car up. Individual drivers often like different feels so over time the need for multiple spring rate options have evolved. Manufacturing processes have improved allowing for all rear end units to create more corner speed. Spring technology allows for ratchets to be custom tailored for specific track conditions or driver styles.

Locker springs are manufacutured in a variety of rates to control the ratcheting action for the perfect driver feel on corner entry. A stiffer spring creates a tighter feel on entry and correspondingly a lighter rate spring creates a more free feel.

Randy Larsen:

Tolerances control has made giant leaps forward. Differentiating rear ends perform better and last longer. As the manufacturing techniques have improved, engineers can find more speed with components that mate up more efficiently. As the science improves, doors of creativity open. Engineers can take advantage of creative ideas as they can count on sound manufacturing processes that produce components that perform every week.

What other tips relating to rear ends would be important for our readers?

Randy Larsen:

Proper venting is paramount to rear end performance. 1/2” hose and a minimum of 3/8” NPT fittings will allow sufficient air volume and rear end breathing. Small hose can cause pressure build up and unwanted problems. Be sure to route your vent line so that oil can drain freely. Kinks and dips in the line will cause oil to pool up preventing proper venting. The vent should be at the highest point possible above the housing. The hose should be routed as straight as possible to avoid areas in the hose where fluid can pool up.

Frank Loverock:

We are constantly developing technology and lighter weight differentials are the result. Differentials differ from lockers as they are free from locking and unlocking.

The differential allows you to run less stagger, about half as much as a spool, depending on the track. Differentials are very forgiving in relation to stagger changes as the gear mechanism is constantly adjusting to the current condition resulting in handling characteristics that stay the same throughout the race.

Jeff Butcher:

All rear end types offer positive choices. The simplicity of a spool is very often fast, inexpensive and maintenance free. Heat is less of an issue and a rear end cooler is optional at many tracks.

The locker creates stable corner entry. Coolers are needed and correct locker springs will speed your car up. You sign up for maintenance but less is required than a differential.

The differential can do many things to add to speed. In exchange for the stagger compensating differential action, heat is created and since there are more mechanical parts - wear and maintenance need to be considered.

In the end, all three types consistently win races. It is not a question of right and wrong. Choosing the correct rear end is specific to the needs of each team and the goals that they have. My teams have won plenty of races with a spool and if you are on a tight budget the simplicity becomes more important. It was fun to win with the free entry of a locker which is often a great choice. At other times the differential will power you to the front and that great feel in the center is something that drivers always enjoy. Teams that choose rear ends based on their own needs are making the “right” choice. In racing, bolting in speed is a myth. Having a nice rear end is always a good thing regardless of the type you like to run with.

Go Forward – Move Ahead
Jeff Butcher
2/1/11

Panhard/J-Bar

Adjusting the Panhard Bar or J-Bar always generates feedback from the driver – sometimes good and sometimes so bad that the crackle from the driver sounds like the speakers blew at an AC/DC concert. Even on TV you hear about 1/8” adjustments during Cup races that take the driver from waving handfuls of steering wheel to driving with one hand. Of course, the same team can try to cure a small tight feeling and raising the bar the same 1/8” can make the car junk. It seems the entire chassis package revolves around what can be a very sensitive adjustment.

So why is the Panhard/J-Bar so sensitive and how come drivers can nearly always feel even small adjustments? I mean the bar is simple enough - all it does is connect the chassis to the rear housing locating the rear end laterally. It’s just a bar with a rod end on each side yet the height and angle seem to do so much.

To help understand why the Panhard/J-Bar is so sensitive it pays to think out all relationships that change based on how it is located. First off, the front roll center gets involved as the roll axis (the line drawn through the front roll center extending through the rear roll center) is affected. As you lower the Panhard/J-Bar you also lower the roll angle and the center of gravity gains leverage because the distance from the roll axis line and the Center of Gravity is increased. The result is a car that rolls more due to the leverage increase and the added distance from the CG allows for roll around an arc with what is basically a larger diameter.

As you raise the roll axis the distance from the Center of Gravity is less and the car rolls less. In this case, there is more of a direct force applied to the right rear tire. Seems so simple yet there is more to think about.

The rear spring rate controls roll so there is a correlation between rear spring rate and the Panhard/J-Bar. In essence, as you run more rear spring the effect of the bar changes – or does it? That giant sway bar controls roll as well. All the things that control roll perform their function in a somewhat progressive fashion and the timing of the control is slightly different. This is the point in the story where engineers and data acquisition get fun but since it is always my goal to remove engineering speak here there are many things to consider. Since the variables are many, the answers change depending on entry speed, banking, braking, track grip, tire grip, balance, aero and the like – no wonder engineers make the big money and are such snappy dressers.

Whenever I face many dynamic variables that change depending on when and where the car is in the corner it is my goal to find a way to simplify in a fashion that allows me to make real world changes at the track. This is where basic understanding of the hardware can help you to draw your own conclusions.

A low Panhard/J-Bar promotes roll. A high one relatively resists roll. The Center of Gravity in the car is the same regardless if you have 100 lb springs or million pound springs. Springs are progressive. A 500 lb spring compressed one inch stores 500lbs. The same spring compressed 2” stores 1000lbs. So the springs compress in roll and in squat. Great.

The Panhard/J-Bar locates the rear end laterally. In squat it does basically nothing. As an example; a drag car is designed to go in a straight line. The drag car only experiences squat (of course there is engine torque but humor me and imagine just squat). In this example you could mount the Panhard/J-Bar on the roof or on the ground and the squat will be pretty much the same.

In our cars that turn left, the Panhard/J-Bar centers the rear end on the straights and then applies force laterally as the car transitions into the corner. Based on the height the springs store energy and as we exit the spring energy is released at a rate in conjunction with the Panhard/J-Bar. A high bar transfers load quickly and a low one takes longer due to the added distance between the Panhard/J-Bar and the Center of Gravity – well at least in an apples to apples situation.

So – the result is we can change the “timing” of roll as well as the loading of the lateral force of the Center of Gravity by adjusting the Panhard/J-Bar. Fabulous – but how much and when do we raise the Panhard/J-Bar verses adding more rear spring rate? There is not an answer to this question unless your car has a 48 on the side. In the end, as you have more grip though a better racing surface, tire compound and more down force then a higher Panhard/J-Bar will transfer loads in a more direct fashion creating quick and sporty reactions. Of course track banking and car speed get tossed in the variable bucket too.

If your track is bumpy, worn out, small and has little banking then maybe you want to slow down the reaction of the car and smooth things out with a lower Panhard/J-Bar. Since I grew up in the Northwest all of our tracks were worn out and we raced on top of shiny rocks. I know I ran Panhard/J-Bars at least a full inch lower, on average, than my competition. We managed to win some and we always were good on the long run so in general a lower bar made up for reduced grip and minimal down force as most of our tracks were small and flat.

Since the Panhard/J-Bar is such an important locating device it is critical that the hardware is solid. Any flex creates unpredictable variables resulting in a car that is erratic. The hoop style shown adds rigidity and creates a solid feel for the driver.

Then we get into Panhard/J-Bar split and reverse split. There are a lot of thoughts on this topic. I hear about how teams think the rear end moves left when the right side of the Panhard/J-Bar is higher than the left. Well – the rear end is stuck on the ground and what is really happening is that the frame and body are moving to the right. Your team needs to think about the trailing arms and the rear steer in relation to the amount of split you are running. You also need to think about your shock angles. If they are perfectly vertical on your coil over car then when the body/frame moves right not much happens as both coilovers shorten by the same amount. If you have the top of your coil over tipped in then as the body/frame moves right you are losing diagonal weight as the car rolls and then gaining it as it rolls back. With tipped in at the top coilovers, if you run reverse split, the body/frame moves left and the LR shock gets more upright adding diagonal weight percentage.

Still, there are many times when you add reverse split that the car turns better even though there is potentially more diagonal through roll. The big reason is that the Panhard/J-Bar was probably too high to begin with and side bite is lost. The car skates in this scenario so lowering the bar creates more grip. More grip allows the driver to feel more secure so he can simply turn the car to the bottom instead of skating up to the second groove. Sure – you can think about how reverse split encourages the rear end housing to be pulled into the track and how standard split (higher on the right side) pulls up on the rear end housing. Last I checked gravity is the same and regardless of how uphill you run the Panhard/J-Bar so I doubt the rear tires will ever fly off the ground due to Panhard/J-Bar angles.

With standard split or reverse split rear steer comes into play. You can use rear steer to your advantage but remember to think past direction the housing moves through roll. Keep in mind that the housing goes the opposite way as the chassis unwinds and sometimes the opposite and equal reaction is more important than the intended action.

A frame side Panhard/J-Bar mount that adjusts quickly can maximize practice time ensuring you have every chance to dial in the car. The slider version allows for precision locating and increments as small or as large as you need.

Even so, there is still more to it. The goal is to get the most out of everything. Maximum down force in combination with soft tires creates an opportunity. Of course, you may have a sway bar in the car the diameter of a sewer pipe so how do we balance the Panhard/J-Bar in association with a ton of rebound in the front shocks and a sway bar that locks down the nose? Again, there is not an answer as “all” of the variables have to come together to create the right feel for the driver.

A J-Bar bracket with a slotted adjustment allows for quick changes. A wide adjustment range with slots verses holes will help your car to find every ounce of speed.

Instead of me telling you the answer to the pop quiz I prefer to write down my thought processes. It makes little difference if you agree – it makes a lot of difference that you develop a consistent system that lines up with the variables that you face. Honestly, the magic 48 has mastered this systematic approach. Sure – they make a ton of horsepower but in the end the 24 and 88 have the same junk. The 48 kids have balanced the HP with the aero, the shocks, the sway bar, the available grip and have come up with a system that allows Jimmy to run aggressive rear weight and ideal Panhard height. I don’t have inside knowledge - but I “know” that Jumping Jimmy, whether y’all like it or not, can run aggressive set ups that push out every ounce of grip cuz Sir Knaus has this formula flat figured out. He approaches the system the same way every week and eliminates as many variables as possible. The result is an edge that allows his team to be better than team mates that are in the same shop. The benefit is that Jimmy can get a little more due to the communication derived from their proven formula that features the Panhard height as a major component in their magic math.

Raise the Panhard/J-Bar when:

1. There is a ton of grip available.

2. When you have high amounts of down force.

3. You have high banking and smooth transitions.

4. When the car is solid and easy to drive deep into the corner.

5. When the driver can pull down a groove at will.

Lower the Panhard/J-Bar when:

1. The driver doesn’t like the corner entry feel.

2. The car won’t stay on the bottom.

3. The track is bumpy or has little grip.

4. When the car feels fast for 2 laps then drops off considerably.

5. When left side tire temps are low.

Think opposite when:

1. The driver says the car is tight yet you have thrown many adjustments at the car that should have made a noticeable difference – none of those adjustments are working. This may be a time when a lower Panhard/J-Bar can add more positive rear steer through added roll helping it to turn in the center. A gain in side bite would be the goal increasing overall grip giving you new chassis adjustment options created by this new baseline.

2. The car needs more side bite so the driver is timid with the steering wheel on corner entry so he misses the apex making him believe the car is tight. Pay special attention if the driver complains that the car snaps loose after being tight in the center as this “can” be an indication that lower is better.

3. When you keep raising the bar to help the car turn and there is little change.

4. Panhard/J-Bars are so easy to move that sometimes it pays to simply raise and lower it a small amount and just use the trial and error method.

While a simple device, the Panhard/J-Bar is basically the hardware that connects the Center of Gravity to the ground thus increasing the importance. Getting the adjustment just right is the key to winning. So when you ask me how high you should run your Panhard/J-Bar my answer will be, “I don’t know – ask the driver”!

Go Forward – Move Ahead
Jeff Butcher

12/1/10

Clear Vision

Back in the day of no helmets and open car cockpits the only need for mirrors was to see if drivers had their Dippity Do hair gel smoothed perfectly on their ruggedly handsome heads. Luckily, I only know about that hair product because my Dad would take a handful and smear it on his once full head of hair – not me! Today, drivers are strapped in their cars with head restraint systems, wrap around head braces, full face helmets, Nomex hoods, window nets, and blind spots that would make Helen Keller a better than today’s “blinded” driver. She could be competitive and prevail over sighted drivers as she was comfortable utilizing the drive by brail system. Sighted drivers have to overcome being out of their element and overcome the mental discomfort created by the limited vision found in cars of today. Helen had no such limitation and subtle bumps of brail came naturally to her. A driver using brail finds much bigger bumps, zero subtly and hard crash resulting in the need for a cane the following day – a cane for injured people, not a white one.

Often I have heard drivers say they would rather not have mirrors as they get annoyed at those few drivers at every track that drive with the mirror to fill up the grove instead of simply driving as fast as they can. Some old school drivers think that mirrors should be removed as they feel as if they take away from their driving skills and they don’t need them. These drivers think if a competing car is up to their door then they will see them. If the car is not in their peripheral vision then it is ok to cut down into the turn. I think this old school thought may have been true at one time. Today it is so hard to see due to needed safety improvements and new thinking needs to be considered even by experienced racing veterans.

Safety advances are clearly the right choice but they do have an impact on vision making the need for mirrors a top priority. More vision means more safety and mirrors are an aid and not a crutch.

At Daytona and Talladega the Cup stars accept that blocking and mirror driving are simply part of the deal. At local short tracks blocking may happen but, to me, the safety aspects of proper vision outweigh the drivers that break the unwritten rule about using mirrors to intentionally drive in an erratic pattern in an attempt to keep pursuers at bay. The reality is that in today’s modern stock cars it is so hard to see that the need for mirrors is very real. Competition is so tight that mirror driving isn’t as easy as compared to the days when drivers had full head movement, open face helmets and seats that stopped at their shoulders.

Modern day drivers have so much going on in their cockpits that it takes full concentration to look forward to hit their marks. Sure, a few guys can block by mirror driving for a few laps but in return their lap times become so slow that they get passed eventually anyway. A few bad apples will always mirror drive but those types are rarely the guys that are in the front week in and week out. Besides, on a quarter mile short track it only takes a few blatant mirror driving moves and the trailing driver with a faster car has a chrome, well plastic, horn that trumps mirror driving. A quick rap on the bumper gives the mirror driver plenty to think about. Mirror drivers have plenty of time to think while being towed off the track when a veteran shows them how the bumper on a faster car functions.

Used properly, mirrors are a safety device that should be employed extensively. If you look close at the Cup cars on TV they nearly all have clamp on spot mirrors on the driver side window opening. Large wide angle rear view mirrors help drivers to know what is going on behind them. With the knowledge that a car right on the driver’s bumper competitors know that full concentration is required. The awareness of close action is a safety necessity. If the track is clear behind drivers can be mentally fresh when it counts as they can take a small mental breath if they know they are not being dogged from behind. With a clear rear view mirror drivers can experiment with different lines in the never ending quest to find more speed.

Many short track teams employ radios and spotters can be very helpful in keeping drivers informed. The spotter’s job is to look ahead and give advance warning of on track trouble. In addition, spotters can help with strategy, discussing chassis adjustments and of course they can be vital in helping drivers to know if a competing car is inside or outside. For drivers, it is quite comforting to hear that it is “clear” all around. While spotters can be an important tool it still comes down to the driving feeling what is going on around him and the decision to pull down at corner lies squarely with the driver. Many race series do not allow radios and the drivers are solely responsible to be aware of their surroundings. Mirrors play a vital role in helping drivers know when it is safe to go low or take the high groove.

A quick glance to the side view spot mirror provides instant information and a good wide angle spot mirror provides a clear view providing instant real time information for the driver to act upon. Increase vision improves speed and cuts down on accidents. Corner entry accidents always create controversy and in the end if a driver can prevent an accident then every tool available should be utilized.

A spot mirror on the drivers side will help you to feel cars around you. A fraction of a second gives you added confidence entering the turn when you know you are "clear". Cup stars may mirror drive but they have the luxory of just getting out another car out of their stable of 20. Saturday night racers usually have one car and when it is torn up the concern is about cost and time to repair. Cup drivers don't even think about cost, time and damage and they have an entire shop getting the next one ready. Mirrors prevent alot of damage on Saturday night if used properly.

Wide angle rear view mirrors are equally as important. Adjusting the mirror to cover blind spots helps drivers to know what is happening around them without the assistance of a radio spotter. While spotters are invaluable – instant information provided by a quick glance allows drivers to make better decisions. Whenever I hear a driver throw their spotter under the bus after a wreck I wonder if a glance to the mirror could have saved a wreck. There is little doubt that stock cars with all the safety gear have limited vision and drivers can only see clearly through the front window. Just about every other view is a blind spot. The side view and vision out the back are severely limited and good mirror installations expand the drivers viewing area immensely.

Wide view mirrors that clamp on can be positioned perfectly eliminating most blind spots. A variety of sizes are available. Glass mirrors offer the best view and multiple bracket options allow you to get the mirror just where it is needed.

I think there should be a rule on every stock car including big time NASCAR racing that requires the use of a Lexan spoiler blade. A spoiler blade made from aluminum prevents trailing drivers from looking ahead through the windshield of the car in front of them. A clear plastic spoiler blade greatly enhances vision allowing drivers to see further ahead. Clear spoilers are a low cost safety measure that should be applied at every track. Why clear spoiler blades are not used on NASCAR Cup cars, Nationwide cars and Trucks is beyond me as the added cost is zero and the vision improvement is dramatic.

Ken Schrader spends a lot of time short track racing. I recall a time when he was driving a late model up in the Northwest and in the drivers meeting he was very vocal explaining to the officials and other drivers the need for Lexan spoiler blades. Schrader was a credible voice and at the time most of the cars were using aluminum blades. After his drivers meeting talk clear spoiler blades became the norm helping to make the Northwest series safer.

Clear spoilers help the driver behind to see through your car helping to avoid your car being pile drived if there is a wreck in front of you. Clear spoilers are inexpensive and they have zero drawback. If you ask me all series should mandate a clear rear spoiler blade.

There are a variety of mirrors available on the market and the clamp on versions mount in seconds. Easy adjustment and mirrors that can deal with vibration are a must. Once adjusted, simple locking mechanisms hold mirrors in place ensuring that drivers can count on clear vision. Clamp on mirrors offer the added advantage that the clamp mount allows for easy movement to provide for perfect placement. Weld on brackets commits the mirror location resulting in a compromise in vision. Clamp on brackets can be loosened is seconds and the perfect mounting location can be found easily and without limitation. The lightweight aluminum construction components are and added benefit.

Using the right bracket will get your mirror placed exactly. Teams should spend the time to eliminate as much blind area as possilbe. With the driver strapped in, a crew member can move about the car while asking if the driver can see the crew member in the mirror at all locations. In just a few minutes vision can be drastically improved. 

Using spotters for guidance instead of as dependence will expand sight lines to safely see your way through an entire Saturday night. Lexan spoiler blades will assist all race series drivers in looking ahead allowing them to identify trouble fractions of a second sooner increasing the chances of avoiding crashes. Perfectly located clamp on mirrors, coupled with their proper use, will give your team a safety advantage and will save tearing up equipment. Amazing new safety gear requires new thinking and the ability to see and feel through your mirrors takes only a little vision.

Go Forward – Move Ahead
Jeff Butcher
10/1/10

Weight Wisdom

They say that the entire universe began as a tiny, and very heavy, object about the size of a marble. One day - this extremely dense marble like object decided to blow up and form every galaxy, planet, and star that is out there today. I am not sure if I totally grasp such a concept. What is clear is that I am watching way too much Discovery Channel and our focus here is making your car go faster. Still, if you could take a tiny sliver of that very heavy marble sized object from the universe on its birthday the little sliver of mass would be perfect for making your race car faster.

When building a new car, creating a Center of Gravity that is lower than your current car will allow for more speed. Physics demands that a lower Center of Gravity will create more grip on an object (racecar) that is going fast in a straight line and then, for reasons that are obvious to drivers, the object (still a racecar) suddenly needs to move violently left.

If you had material that was extremely dense and heavy such as a tiny chunk from the marble like object that created everything, you could use this heavy material to make your car consistently faster. Lead is commonly used to balance out racecars because it is dense, melts easily and is relatively inexpensive. The melting point of lead is a mere 621.5 Degrees F and it well suited for molding to nearly any shape.

Lead is less than healthy though and fumes, grindings and over handling should be avoided. Food while working with lead is forbidden. Researching the web for proper lead handling is a great idea. After finishing your lead handling research, and fitting lead for your application, it is easy to add a quick paint job to your completed lead blocks to assist in reducing unwanted exposure.

Lead costs less than 2 bucks per pound. 1 Cubic Centimeter of lead weighs in at 11.35 grams and steel comes in at 7.85. In a perfect world, you could use tungsten for your car ballast which weighs in at 19.35 grams per Cubic Centimeter and is very safe to handle. Too bad tungsten has one of the highest melting points on earth at about 6170 degrees F. Tungsten costs about $13.00 per pound or more. Regardless of your ballast material, the earth element lesson is utilized to help illustrate a point. Tungsten weighs about 1.7 times as much as lead which means you could take up almost half the space with Tungsten ballast as compared to lead. The smaller mass allows you to build in more adjustability. A small sliver from the big bang marble of the universe would be really efficient – let me know when you find a supplier for the mythical and magical material.

While safe, tungsten is one of the hardest materials on earth making it difficult to work with. Maybe you can find usable chunks at a discount from a surplus company. If you have some Osmium or Iridium laying about this would make excellent racecar ballast – of course finding these elements might prove to be very hard and very expensive. Guys in black suits would probably fly in from Area 51 to see what is going on in your race garage.
The point we are making is that we want our racecar ballast to be located in the smallest area possible verses being spread about the car. We work hard and spend big bucks on light weight materials for our cars so that we can add ballast for adjustability. It pays to locate car batteries low and left. Dry sump tanks are best mounted far to the left. Anything that is required in the car should be mounted in the lowest possible position and as far left as you can get away with.

Example 1: Side Weight - The example above shows two hunks of lead on the left frame rail and 2 equal chunks on the right frame rail. Locating lead in this fashion might show desired weights statically on the scales but when you put the car in motion this car will be slower than a clone car that has lead located in a centralized fashion.

Super Modifieds take the low and left thought to an extreme and their Indy Car looks are only given away by the giant V-8 engine that hangs completely outside the car to the extreme left. Super Modifieds are very fast and they are incredibly lightweight, have a very low CG, have a ton of left side weight and have massive horsepower. The only thing holding them to the ground is the giant wing that controls corner entry and down force.

When mounting lead in your stock car you always want it low. Your goal is to reach the maximum left side weight allowed by your rules with the lead in a compact area. By placing the lead in a compact area your car can handle the weight with more efficiency.

If you place lead in the left frame rail and another chunk on the right rail then the car will not be as efficient and on paper it will be slower than the same car with the ballast placed in the ideal location. With improper positioning of the ballast the tires will wear faster, the shocks will get hotter and the maximum car speed will be less than if you placed the lead in a compact area. You may need to manufacture your lead in shapes to fit in the ideal spot between your frame rails.

Example 2: Center Weight - Our hypothetical car shows the lead from Example 1 moved to the center of the car. In Example 2 we have the exact same amount of weight and are at the legal minimum and the maximum left side percentage. The shocks, springs and tires are much more efficient due to the proper location and centralized layout.

Your goal is to have the lead low and built for adjustability. Filling the left rail and then filling the right rail gives you the static numbers on your scales that might allow you to write down the set up numbers aimed for. The trouble occurs when you put the car into motion. Having lead on the left and right rails creates a situation the motion is harder to control than if the lead centralized. The lead on opposite sides of the car creates a back and forth rocking force that must be controlled by the springs and shocks. Located properly, the back and forth motion is reduced as the lead is centralized and supported between the springs and shocks for efficiency.

To illustrate further, school has started and many of you are loading your children up with books, computers, lunches, IPODS and cell phones. All of these items go in their backpack which is centered between their two tiny legs. The weight is carried so that the mechanical leverage of the human body can most effectively hold the weight while utilizing the least amount of energy. To improve conditions for your kids, making the back pack lighter is the best option. I am certain that parents would not load their kids down with extra weight and then make them carry the weight outside of their body center line. Kids wouldn’t be asked to carry two backpacks with their left and right hands extended out away from their body center line. I doubt parents would feel the need to add weight to one back pack in an effort to make the back packs the same weight and increasing the overall load of their little ones.

Our racecars (babies!) feel the same extra work when ballast is spread out with some lead on the left rail and some on the right. Ballast needs to be centralized so that the suspension can manage the inertia and centrifugal force efficiently.

Example 3: Rear Weight - Placing lead behind the rear axle might read the correct percentage on your scales but placing lead behind the axle is not recommended. Weight mounted behind the rear axle will cause the rear tires to overheat quickly and the car will be difficult to control. Ballast should always be mounted between the axle center lines for maximum potential speed and efficient control by your springs and shocks.

Less weight is always the better answer for your racecar and extra weight should never be added to gain more left side weight percentage or rear weight percentage at the expense of the overall total. In other words, you should never run over the legal minimum weight to get up to the maximum left side weight or any other number for that matter. Run as light as the rules allow and if your car is below the maximum left side allowable weight then find something in the car to move left but never add weight above the legal minimum.

Locating components in your car properly can help you to maximize weight distribution for ultimate potential speed. the clamp mounts on this radiator mounting system allow you to slide the radiator as far to the left as your frame allows. This mount also adjusts up and down ensuring your radiator is fit properly in the car. Creatively planning the low and left mounting goal of all of your required car components will help your car get through the corners efficiently.


The minimum legal overall weight is always the most important number otherwise our babies (racecars) will get tired by the end of the race. Shocks will overheat and tires will give up - just like kids that are carrying back packs with too much improperly placed junk in them. For your car to go faster, less weight is always the correct choice. The weight you add in ballast form should be concentrated in one area to allow your car the most control over the entire race distance. Your frame rails are much smaller than the universe and it only takes a little pre-planning to properly place ballast keeping your team from being in outer space.

Go Forward – Move Ahead

Jeff Butcher
09/1/10

Just Breathe

Finishing races begins at the start – in the garage to be more precise. The adage of “to finish first you first must finish” begins with car maintenance and construction. More than once I have seen cars hit the track for the first practice session only to spill fluids all over the place. When the smoke clears, the result is usually a load of engine oil or gear lube all the way around the track. Usually, the leak is unknown to the driver and the mess always seems to be square in the middle of the groove.

Overfilling fluids is a common cause of leakage and often errors in the venting system create the trouble. Fluid management and proper venting practices are simple. With a few tips your team can avoid being the practice killing culprit. How many times have you seen team oil down the track at the first race or practice of the year? Unfortunately, major track oil downs seems to happen every year - at every track and at every division. Luckily, a British Petroleum Gulf Coast top kill operation isn’t needed. Simple construction tips and standard care get the job done. If nothing else maybe some conversation on the topic will save a few tracks from the dreaded oil downs.

Since most late models run quick change rear ends it is easy to find the proper fill level as site plugs guide the way. Rear end pumps and auxiliary coolers can complicate fill levels so it pays to fill the system with a predetermined amount of fluid. Knowing the exact amount to fill your rear end speeds gear changes at the track and eliminates the chance of over filling. The next time you drain your rear end simply measure the amount of fluid. With the results you can then pre-package the correct amount for a quick refill.

For rear ends, a tank with a reservoir is a great idea. Rear end heat is excessive and controling the fluid and heat is a real issue. Mounting the tank up high with a line that allows gravity to return fluid back to the rear end is recommended.

Your rear end breather system, while simple, needs a few tricks to keep your rear end fluid in the car. A baffled vent tank provides added insurance. A roll bar mounted or sheet metal mounted tank version will work on any late model. Mounting your rear end vent tank as high as possible is a good move. Gravity helps any fluid that runs up the line to drain back into the rear end.

Simple things like using a 3/8” minimum rear end vent line help as well – smaller vent lines are prone to clogging. Be sure that the vent hose runs in an S shape but avoids droops in the line where oil can collect thus blocking the air from traveling to the vent. Your vent hose must run continuously uphill from the rear end to the vent. Any hose sag could clog the vent system and you will end up with rear end pressure build up and leaks at every gasket.

You can use a standard vent on the rear end without the baffled reserve tank. Going this route saves a few ounces of weight and if everything in your rear end and in your filling process is done correctly a vent without a reserve tank will work fine. For me – the insurance of a baffled reserve tank on the rear end is a wise choice. The small cost and weight difference give you added insurance.

Rear end heat can be very intense as noted by the fine stench in your garage after a 100 lapper. The overall oil volume in your rear end is small and it does not take much overfilling to create leakage. The heat experienced in a rear end leads to high expansion rates so a baffled tank wins out compared to saving a few ounces with a vent that does not include a reservoir. Vents without reserve tanks work great for venting axle tubes and transmissions.

Engine venting is another easy to design system yet again we see cars oil down the track every year due to overfilling the dry sump tank or improper venting. With a dry sump system a sealed system at the engine seems best. Valve covers are unvented and the typical vents are replaced with a number 16AN line connecting the valve cover with a return back to the vented dry sump tank.

A dry sump breather tank should include internal baffles and plenty of vent area. Running your vent line with out sags wil prevent oil from collecting in the low spots in the line ensuring a free flow of air for proper venting. The sump tank shown includes a drain valve for easy maintenance.

Measuring your dry sump tank to the correct level is simple. A dip stick works fine but you do need to guard against any oil that is in the pan. With a dry sump the pan should have minimal oil but it is good practice to verify the pan is dry and verify that your sump tank level is in the safe zone..

A number 16 AN line from a valve cover back to the sump tank is a proven venting method. The venting is done at the dry sump tank and the engine is “sealed”. Your #16 return line needs to run downhill from the valve cover to the sump tank. At the sump tank, a line is run to your dry sump breather tank and again gravity needs to be considered. The line from the sump tank to the breather needs to run uphill in a sag free fashion.

Since transmissions generate little heat, in comparison to engines and rear ends, a simple vent can be used without a reservoir. The idea is to simply vent transmission pressure due to heat expansion. If you mount your vent as high as reasonable a simple tank less vent will do a great job of keeping fluid in your transmission. That said - taking the simple step of running your vent line without line sag is a great idea. A baffled tank is always a good idea but at the transmission the added insurance is not a requirement as compared to the engine and/or rear end.

A vent without a reservoir works fine on transmissions and axle tubes. Lower pressures and less heat generated in these areas allow the lightweight and inexpensive simple vents to function properly. As with all vents be sure the vent hose is free of line sags so that oil doesn't pool up and impede the venting process.

While you radiator cooling system is completely sealed, an expansion tank will help your car run cooler and ensure you are getting the most from your cooling system. Installation is simple. A ¼” NPT is recommended for an air line bleed. A ½” line is connects to your water pump. The 1/8” fitting allows for venting when your cap pressure is overcome and can be routed to a visible place such as the windshield to alert your driver to a heating problem. The reserve tank gives you the extra capacity as the car reaches the maximum safe water temperature. Routing the vent hose to the windshield gives the driver early warning allowing you the opportunity to identify and repair cooling system issues before they take you out of the race.

Roll bar or panel mounting of reserve tanks works on nearly any car cooling system. Remote vent tanks often include a billet cap filler neck for added security and durability.

A cooling system expansion tank can help you car run cooler. Note the billet filler neck for added cooling system reliability.

Venting your fluid systems properly will add to the longevity of your drive train and help you to avoid embarrassing oil downs.. The tale tell strip of leaking fluid follows you to your pit area for all to see and with simple common sense vent installation you can keep your fluids where they belong.

Go Forward – Move Ahead

Jeff Butcher

8/01/10

Make or Brake

When I was helping my Dad work on racecars, at the age of 12, he taught me that 4 tires work better than 3 for the best corner speed. The same thought applies to braking – 4 tires work better than 2. Ensuring that your brake system is set up properly will gain you speed throughout the race. Teams that spend the time and think out the variables will beat their competition by out working them and the cost is generally effort over big dollars. Getting the most from the rear brakes will make your car faster and easier to drive. With more braking power your car will be there at the end every time.

To get the most from your brake system you will want to get the rear brakes to do as much of the work as possible. Often teams and drivers run a disproportionate amount of front brake as pushing the window on rear brakes can make the car loose on corner entry. While too much rear brake can cause entry problems, there are some basic ideas that will allow you to run more rear brake. The goal is to take pressure off the front brakes. If your car constantly has front brake rotors that are glowing red then perhaps the cure is to get the rear brakes to do as much of the work as possible. Maximizing your rear brakes is a key ingredient for long lasting speed.

Feeding your brake system with cool air will help your components last and make your car faster at the same time. For this application a single hose gets the job done, but two hoses are often a good idea. The odds are stacked in your favor if you spend the time to saturate your brake components with plenty of cool fresh air.

A proper brake balance bar set is a simple place to start. Following the manufactures brake balance bar set up sheet will prevent many problems. Often I have seen brake balance bars that allow the rear master cylinder to engage before the front. When this occurs the car will be unstable on corner entry and regardless of how much front brake you dial in the car simply will not be fun to drive. Read the manufactures brake balance instructions thoroughly. You can check your car easily as the brake balance bar should be perpendicular to the frame when the brake pedal is depressed. If your balance bar is perpendicular to the frame at zero brake pressure then it is likely that the rear brakes will engage first. Whenever the rear brakes engage first you can bet handling problems that are impossible to overcome will follow.

Another common brake balance bar set up problem is proper clearance at the clevis. Refer to your manufactures instructions but in the end the master cylinder rods should be parallel and the components should have enough clearance to prevent binding throughout the brake balance adjustment range and through full pedal motion. Without proper clearance the brake balance adjuster can bind up during the race at full rear or full front bias making for a tough night.

Drivers play a role in maximizing rear braking as well. Brake smashers will require more front brake bias whereas smooth braking drivers can run more rear brake. By spacing out the time between lifting off the throttle, rolling in, and then applying smooth braking pressure provides the opportunity for teams to get more from their rear brakes. Smooth drivers that are easier on tires often get the most from their brakes.

Selecting the right friction material on your pads will help you with your goal of running more rear brake. Heavy brake users almost always end up with harder pads on the front whereas smooth drivers can use softer front pads. Finding the right combination for your car, driver and brake system can be a trial and error process. You can speed the process by working with your pad manufacturer or the parts supplier at your track. Typically, your parts supplier will know what competing teams are purchasing. Your team can tailor choices based on the appropriate variables and your crew usually knows if your driver relies on heavy brake pressure. If you build your system right you can win races with a heavy braker or with a smooth driver. If you have a brake smasher encourage using less brake pressure but remember that it is hard to change a driving style.

Rotor and caliper size comes into play – if you run lightweight components you will build brake temperature very quickly and can overstress undersized parts. Initial stopping force may seem fine but if you go through center on the heat range then the components become too hot and the heat is not dissipated properly due to the lack of mass. Warping and glazed pads are common results when under sizing brake components. When the heat induced brake fade occurs, the result is a natural adjustment of adding more front brake bias. For short tracks I would always choose the extra weight associated with a good brake system verses compromising braking efficiency and longevity. The weight savings offered by brake components that are too light is not worth the negative results.

Proper brake ducting is a must. For short tracks I would worry less about aerodynamics and drag and focus on keeping the brakes fed with plenty of fresh cool air.

Locating your brake ducts towards the center of the nose will feed your brakes with the most air. As you move towards the outside of the nose the air moves around the car and not through your brake ducts. Mounting the brake ducts as close to the radiator opening pulls in the most air.

Pulling air from the center of the nose as close to the radiator opening as possible improves airflow to your brake system. If you place your ducts too close to the edge of the nose air goes around the car instead of through your duct work. Keeping your brake system cool is a priority over the minimal negative aerodynamic effects. For short tracks good brakes prevail over any aero advantage.

In line fans are an efficient and inexpensive way to keep your brakes cool. For short tracks fans are a must. They are lightweight and with a flip of a switch they can be turned off if needed.

Rear brake ducting is not always needed but I think it is a good idea. Fresh air to both the front and rear brakes helps the components last longer and can prevent seal damage, fluid boiling and pad glazing. As we focus more on rear braking power then proper ducting comes into play.

Adjusting your car with a brake balance adjuster during the race can be your ticket to victory lane. When you have a tight car dialing in more rear brake can be an easy cure. A loose entry is often fixed with a few turns to the front. Selecting a brake balance adjuster that has an easy to reach handle helps drivers to make bias changes under race pressure. Adjusters with ball detents ensure that the bias adjustment stays put and the detents assist in monitoring the front to rear bias setting.

Using a brake balance adjuster system with an easy to reach handle and ball detents helps drivers to maintain the desired brake bias setting under race pressure. This model has heavy duty flexible connection hardware that eliminates binds at the balance bar. The lightweight construction bolts to your car fully assembled due to the mounting hole layout. Be sure to check your manufacturer's instructions for the proper brake balance installation.

Choosing high quality fluid in the smallest containers possible is another critical braking rule. As soon as a bottle of fluid is opened it begins to deteriorate. Moisture in the air reduces the boiling point nearly instantly so it is a good idea to use only new bottles when filling your system and toss out partial bottles right away. Once opened – brake fluid will never be as good as a fresh bottle.

Bedding brakes is an often overlooked area. Rotor bedding and pad bedding are to separate processes. Be sure to clean new rotors removing any oils or foreign materials. Rotors need to be brought up to operating temperature slowly and then returned naturally to ambient temperature.

When bedding rotors I recommend taping off most of the duct work and ask the driver to bring the brakes up to temp with several stops. A few stops at easy pressure and then several at medium pressure. Just simple brake stops without being overly aggressive. Upon returning to the pits I get the car on stands and rotate the wheels every few minutes to prevent the pads from sitting in the same rotor spot during the cooling period for even heat dissipation. Proper rotor bedding will provide for longer lasting rotors and reduces the chance of heat cracking. Once the rotors have cooled completely your driver is ready to use the brakes at their discretion.

For pad bedding follow the manufactures instructions but be aware it is a needed step. Bedding pads properly cures the pads and preps them for race conditions. Bedding improves stopping power and prevents pad failures. When bedding pads on used rotors, be sure to remove the existing pad material off of your used rotors. This is especially true when changing pad compounds. A vibrating or DA type sander with medium grit sand paper will work fine. Cleaning off the existing pad material from used rotors allows your new pad material to mate to the rotor for consistent performance.

With a few minutes of time you can improve lap times by helping your car to stop efficiently. Using all four tires to get your car deep into the turns is much better than using just the front 2. By spending the time to set up your brake system correctly, you can use effort verses money to gain long lasting speed. Stop and take the time to use the braking action to help your car go.

Go Forward – Move Ahead
Jeff Butcher

07/1/10

Caster Creativity

Why do we need a caster? The most direct answer is for directional stability. Without caster our racecars would wander, in an unstable fashion, on the straights and be hard to handle at high speed corner entry. Positive Caster allows the front wheels to trail behind the caster line for true tracking. Extending a line from the top ball joint though the bottom ball joint creates the caster line or caster angle. If the line extends forward of the lower ball joint and contact patch you have positive caster – behind is negative caster and both are measured in degrees. Positive caster allows the wheel to trail behind the line for stability. The most common and easy to understand example is a shopping cart wheel. As soon as you move your shopping cart forward - the front wheels spin and trail behind the positive caster angle.

Caster is measured in degrees. When a line is extended from the top ball joint through the bottom ball joint the caster line is created. Zero caste would be when the upper and lower ball joints create a line that is perfectly vertical. Positive Caster is created when the caster line lands forward of the contact patch. Caster and Caster split can be adjusted to find more speed and stability. A common example of caster is a shopping cart. As the shopping cart is pushed forward the front wheels spin back and trail behind the caster line.

Caster creates stability as the geometry created forces the wheels back to straight. The front wheels are “encouraged” to stay straight as turning them involves lifting the car weight. Expensive street cars often have high amounts of positive caster providing them with a superior and stable feel. The drawback comes in the form of added steering effort. The invention of power steering has allowed for more caster to be added. When power steering fails it is easy to see the negative effects. As soon as the dripping wet driver gets out of the car and asks for help opening a beer due to his arms being worn out it becomes clear how power steering has allowed higher amounts of caster.

In stock cars, we can use caster to help our cars going beyond simple directional stability. Caster split is often used as a chassis adjustment. Running more positive caster on the right than on the left is common. The question is how much split and how much positive caster should you run?

Caster split and the appropriate amount chosen is one of those chassis adjustments where there is not a magic amount or a right or wrong answer. If you understand the effects of caster split you can make your own decisions based on your track, driver and goals. Commonly crew chiefs run 3 degrees positive on the right side and 1 degree positive on the left side. At times it may pay to run 4 or 5 degrees on the right and .5 degrees positive on the left. It all depends on what you are hoping to accomplish for your specific chassis needs.

An often overlooked element relating to stock car caster is that the more positive caster you run the more “beneficial” camber gain you will get. As the car rolls you will see more negative camber gain on the right side and more positive camber gain on the left in lock step with running additional caster. Camber gain through travel is typically a good thing but like all adjustments you want to avoid going too far. If you are aggressive with A-Arm lengths that create high amounts of camber gain you want to be careful that you do not get to aggressive with caster. As always balance applies.

You can find a "speed secret" by understanding that more caster beneficially adds to negative camber gain on the right front and more positive camber gain on the left front. You can check this effect by measuring your camber gain at your current setting and recording the numbers. Next - add caster and check your camber gain again and you will see the benefits visually right in the shop. With the knowledge you can tailor your set up package to overcome obstacles presented by your car, track and driver.

To visualize the benefit of the caster induced camber gain it pays to think in extremes. If you are running 3 degrees of positive caster on the right this would be in the normal range. For our visualization, picture adding caster until the caster line is adjusted an exaggerated amount until it becomes completely horizontal. At this hypothetical and exaggerated point, the result would be pure camber change instead of directional change. The benefit is that with more static caster, the right front wheel would gain more negative camber as steering input is increased. The left front wheel gains more positive camber as the wheel is turned. Cool, we get more camber gain when we need it most by running more caster through a left hand turn! Even experienced crew chiefs can be unaware of the relation to caster and beneficial camber gain in left hand turns. Personally, I find understanding the camber gain from caster to be a true “speed secret”.

Running more caster on the right side verses the left is an adjustment tool that can help cars turn left. The amount of caster split can create benefits as the wheels are turned. More split will “de-wedge” the car at maximum steering input helping the car to turn in the middle. As the steering wheel is un-wound - wedge is added back helping the car to hook up better on exit. Wedge is added back as the wheels return to straight or even back through to the right. You can easily see this change when you have the car on scales. The next time you weigh your car and you have recorded your race ready numbers simply turn the steering wheel 10 degrees left and you will see your scale numbers display less wedge when the wheels are turned left.

You can use turn plates to help measure caster. Using a quality caster camber gauge the turn plates allow you to turn the wheels exactly 20 degrees for precise caster measurements. You can also use the turn plates to visually see the caster induced camber gain when running higher amounts of caster. Simply check the camber gain with the wheels straight and compare the camber gain numbers to your results with the wheels turned 10 degrees left.

 Based on the prior paragraphs it would make sense to run high amounts of caster and plenty of caster split yet understanding the concept will create speed whereas just throwing in aggressive settings could set introduce problems – it pays to understand your changes in advance. Too much of a good thing leads to trouble. There are many variables to consider when it comes to caster amount and split. You must consider other geometry choices such as A-Arm length to avoid ending up with too much camber gain. Too much split can make the car pull too hard to the left making the car tough to control in traffic and on corner entry.

You can thank power steering for creating options with high amounts of caster. Power steering overcomes the steering effort and in the past high amounts of caster was simply not possible as the effort required wore out the driver in a handful of laps. Prior to power steering it was quite common to run negative caster on the left front to reduce steering effort.

For less experienced drivers, I recommend running as much caster split as you can get away with. Something in the neighborhood of 4 positive on the right and 1 positive on the left will help your rookie driver. The idea is that the split will help them to catch the car when it gets loose preventing them from spinning out. As the rookie drive unwinds the wheel wedge is automatically added back in giving the rookie a little help anticipating the loose car before they go for a ride. The split gets wedge back in the car quickly as they correct back to the right giving them security and a helping hand. For rookies, I might compromise my faster caster set up to ensure they finish races. Giving rookies caster split builds their confidence and helps to prevent them from getting behind on the steering.

On most stock cars the top A-Plate is set back to build in the positive caster that most people run. Using slotted A-Arms and slugs makes for quick and consistent adjustments at the track or in the shop.

For experienced drivers, that have a good feel, I might reduce the caster split. The chassis premise is that you know your good driver and you can allow him or her to drive the car without interference from overdone geometry. Again, there is much to consider and other chassis goals would easily override this choice. The experienced driver feels the car and sometimes wants the control in their hands as they anticipate with confidence. In this case, they want to turn the wheel for the desired effect verses being forced into a geometry change that happens outside of their steering input control.

I would push the window on caster amounts and splits on tracks that are smooth and with sweeping corners. If the driver can consistently turn in and unwind the wheel smoothly then adding caster and split can help find speed due to the geometric benefits discussed.

All that said – caster and caster split is very much car, track and driver specific. In much of the country our short tracks are worn out, bumpy and the corner transitions can be abrupt. For rough tracks where drivers are constantly sawing on the wheel, too much caster and caster split can cause the car to be erratic. All the directional change from a steering wheel that is being turned back and forth quickly will upset the car. You can imagine that turning the wheel quickly back and forth would inconsistently put wedge in then out, back and forth steering input would add camber gain then abruptly take it out.

At rough tracks or if your driver nervously saws on the wheel – you will definitely create too much of a good thing resulting in a car that never knows quite what to do and stability is lost. Many of the races my cars won were on rough tracks and I commonly ran 2 degrees positive on the right and .5 degrees positive on the left. The idea was to keep the consistency in the car over the bumps and through quick back and forth steering input. I truly believe this to be one of my speeds secrets at rough tracks. Maybe my competition was being aggressive with their front end settings causing their cars to fade later in the race on the worn out surfaces. That is why they throw the green and checkered flag as there is not a right and wrong here but simply a competitive choice.

Your team can analyze your track, car and driver to see if the benefits of added caster and caster split would overcome obstacles that you face. Used properly there is plenty of speed to be found in the correct caster settings. Your job is to understand the changes through chassis roll. Through understanding you can use caster to create speed and your additional “planned” choices will give you an edge over your competition.

Go Forward – Move Ahead

Jeff Butcher

6/01/10