How to Perform at the Race Track

We want to provide tips on how to do various things while at the race track. Many things are easily done at the shop where we have a mostly sterile environment, but things get messy when we go racing. Here is why.

When I walk around the pits, I either see techniques I never saw or knew before that are a better way to do it, or I see things that are done wrong, in my opinion. I like to think of myself as a student of processes. That means I am forever looking to do things in a more organized way, more accurately, and easier, the emphasis on easy.

So, here are seven processes that we hope you can learn from us how to do better. If you see where any of these could be further improved or you disagree with what we are saying, please let me know and I’ll make adjustments in future presentations. The idea is to get you thinking about each process and to establish a routine and more efficient way to do them.

Set Track Ride Heights – Every race car needs a set of constant ride heights. You normally set these at the shop and maintain them for the life of your car using your setup according to your track rules and common sense.

If you ever have to replace the right front upper and lower control arms, spindle and maybe a front clip, you will go back to your original ride heights to reset your cambers, casters, weight distribution, bump to shock spacing, etc.

When you get to the track, you may be making changes to your spring rates or other settings. So, you need to measure your track ride heights. The problem with the track setting is that the ground, or concrete if you’re lucky, is not level like your shop was.

Pick a place to park your four tires and mark those spots so that when the car is in the pits, it is always on those spots. That is the first step. Then measure your ride heights in a different way than you did in the shop.

In the shop, we usually measure from the floor to the frame at four points. At the track we need to measure this differently. You can do this a number of ways, but try to understand the process and why we are doing it and find the best method for your car.

Many teams measure from the bottom of the rim to the wheel opening directly above that. Or, you can measure from the bottom of the rim to a mark on tape on the fender and set the mark to an even inch. If you don’t have fenders on the front, you can measure from the top of the ball joint stud to a point on the tubing near the shock mount or wherever is convenient.

Recording these height references helps us when it comes time to make changes so that we don’t change our weight distribution either statically or dynamically once we have determined what works best for our car.

Spring Changes – After doing the above process, we can now make spring changes without affecting anything else. The most common thing that goes wrong with making a spring change is inadvertently changing the weight distribution. To prevent that, we refer back to the original ride heights.

Once you have established the track ride height references, you can make spring changes, one at a time. Never try to change two springs at the same time. It might work, or it might not. Just do one at a time.
With the car on the pit marks, jack up the corner that you want to make a spring change. If the spring is stiffer than what was in it previously, you’ll need to back off on the spring adjuster because it won’t compress as far with the same loading. Here is how to calculate the difference to speed things up with the change.

If the old spring were a 10 inch spring and its compressed height at ride height were 8 inches, then it compressed 2 inches to support the load. If the old spring were a 300 pounds-per-inch rate (ppi) and the new one is a 400ppi 10 inch spring, divide the old by the new. You get 0.75. Multiply that times the 2 inches to get 1.5 inches.

The new spring will compress a half inch less than the old spring, so back off a half inch on your adjuster ring or screw. For your springs, just substitute your spring rates and compression amount to determine how much to change your adjuster. You’re not done yet.

Once you have lowered the car back on the ground, shake it down and re-measure the ride height using the references and make changes to the spring height as needed to get your ride height back. It shouldn’t take much if you did the calculations.

Ride Height Changes – As you test your car in practice, it might be necessary to change your ride heights. This can get complicated if you are running bumps, There is a way to do this without messing up other settings in the car.

Most of the time when we feel the need to make ride height changes, it is with the front end because the frame or cross member is hitting the track. This goes for dirt or asphalt. So let’s discuss doing this with and without bumps.

First off, with bumps, we are hitting the track because we are contacting the bumps too late or allowing the shock to compress too far. If we add packers, or spacers, to the area between the shock and the bump, we can raise the car when on the bumps, which is when we are in the turns and the part of the track where we are bottoming out.

When running bumps on both sides, always add the same amount of spacing to each of the front shocks or you will alter the load distribution through the turns and your handling will change as a result.

If you are only running one bump, you have to do this differently. Add the amount of spacing you think will keep the frame off the track on the bump side. On the other side, add the amount of turns on your ride spring adjuster that will equal the amount of spacing. If the bumps spacing were increased ¼”, then adjust your other side spring down ¼” too. This may not perfectly compensate for load changes, but it will get you closer.

For teams with cars having shock screw jack adjusters and running bumps on both sides in the front, you would screw the shock down the amount you think necessary to keep the frame off the track and then move the coil-over adjuster ring up the same amount. Do the same amount of movement to both sides of the car.

Because you are changing the dynamic ride height, your dynamic cambers will change, and so the static cambers will need to change. You are traveling less, so the RF camber will need to be increased in the negative direction and the LF camber will need to be increased in the positive direction.

If you are running soft conventional without bumps, this is your process. In the above examples, we made changes to the static camber settings based on ending up in a different place, or having less overall travel. Not so for conventional setups.

When you raise your ride height to keep the frame from hitting the track, the front will travel the same amount as before, so your camber change will be the same. So, you only need to change your static camber back to where it was before the change to ride height and you’ll be good to go.

Checking Your Alignment – There are several alignment settings we might need to check when at the track. There is front toe, rear toe, and rear alignment related to the front tires. In all of those cases, we need to prepare the car first. In this example we are assuming you are using the tire sidewall to check the alignments.

Every tire has sidewalls that are irregular in shape to a certain extent, or could be. We need to find what we call the high side and position that side of the tire to the top at each wheel. So, we jack the car up and rotate each tire to find the high side, or part which sticks out the most.

Once you have the tire off the ground, place a jack stand next to the tire sidewall and place a screw driver or other object onto the jack as a reference point to where the tip is very close to the sidewall away from the lettering.

Next, have someone rotate the tire while you observe the gap between the reference point and the sidewall. For most tires, the gap will change. Move the reference in towards the tire until it touches the high point. Mark that point and move it to the top. Do this for every tire you will be working with.

Now you will be able to check your toe settings without errors caused by sidewall irregularities. You can also check your rear alignment more accurately. But before checking that , be sure to check the rear toe.

If the rear toe is very near zero, we can go ahead and check the rear alignment. Run a string beyond the two tires on the right side of the car. Tie it to two jack stands and at a height equal to the center of the hubs past both right side tires. Move the string to where it is a reference distance off the front and rear tire sidewalls. For the rear, use the back sidewall only for now.

Here is where it gets a little tricky. If you want the front and rear tire contact patches to line up, you will need to add the cambered offset from the front tires to the reference distance. For an 85 inch tire with 5 degrees of camber, the offset is 1 1/8” based on making an adjustment for the rear tires having 1/4″ degree of camber due to tire stagger. Estimate from that what you need to add. If you want the rear tire contact patch to be offset from inline with the front tire contact patch, then add or subtract further to establish the front offset.

At the front, you will need to turn the steering wheel so that the distance from the front and rear sidewalls are the same after you add the offset. As you do this, you’ll need to recheck and readjust the rear string position off the rear tire. Now take a measurement from the string to the front sidewall at the rear. It should be the same distance as the rear offset for that tire. If it is more, the rear end is aligned to the left. If it is less, then the rear end is aligned to the right from straight ahead.

Changing Gear Ratio – We often need to change our gear ratio to regulate our top RPM, or where we hit the chip if we are restricted to a defined high RPM amount. If we know what RPM we need to achieve, we can do a calculation to find the right gear, but it is not a direct ratio because of the power curve.

Say we have been running a limit of 6800 RPM and we change the chip to a 7200 RPM chip. What gear will it take to top out at the higher RPM at the same point on the race track?

For an example, let’s say we are running a 4.69 gear and want to make the above change in RPM. If the engine power were the same for each RPM, then we just divide the higher RPM by the lower and multiply that number times the old gear ratio to get the new ratio. In this case it is 7200/6800=1.0588. That number times 4.69 gives us 4.96. That’s easy, right?

But what if we have 5 or 10 more HP at the higher RPM? The car will gain speed faster and get to the new RPM quicker and at a point on the track back from where we need it to be. The engine will over-rev past the 7200 RPM or hit the chip sooner than we want.

If the engine were producing 410 HP at 6800 and 420 at 7200, we could divide the lower HP by the higher to get 0.976. We know we need to run less gear to keep from over-revving, but by how much? Multiply the RPM ratio by the HP ratio: 1.0588 times 0.976 = 1.034. That new number times the old gear ratio of 4.69 = 4.85.

This is what happens when we change gears. We move to a new part of the power curve and either gain power or lose it. When making gear changes, we need to compensate for the power difference in order to reach the desired RPM goals.

How To Use A Spring Pre-Loader – It is becoming popular to use a spring pre-loader to facilitate using a softer spring in the RR corner of an asphalt late model or possibly other classes. The reason this is done is to provide the support that the car needs to be balanced through the turns, but allows a softer rate for acceleration off the corners.

The idea is that a preloaded softer spring will have the same force as a higher rate spring. For bump setups, the RR spring is usually a good 100 to 125 pounds stiffer than the LR spring. When loaded statically and through the turns, it has a pre-determined amount of force that it needs to do the job. Let’s investigate how much force is required and how much we need to pre-load the spring.

If our example car normally has a 275ppi spring in the RR corner and it supports 550 pounds of load, then the spring will compress 2.0 inches at ride height. If through the turns it compresses another 1.0 inch, then there is another 275 pounds of force on that spring. So, total, we need to generate 825 pounds of force.

If our LR spring is a 175ppi spring, then we need to make the RR spring less than the LR spring to aid in acceleration off the corners. If we install a 150ppi spring in the RR, we need to pre-load it to 825 pounds or so. Then once the car accelerates and more load transfers to the RR, the spring will compress like a 150ppi spring beyond the pre-load amount.

To get 825 pounds of force into the spring, we need to compress it 5.50 inches. The only way that spring will move is if that corner has to support more than 825 pounds of force such as when the car accelerates and causes load transfer off the front to the rear.

It is possible for a modern late model to transfer 300 pounds upon acceleration. If half of that transferred load ends up on the RR corner, then that is 150 pounds more load and the RR corner will compress another inch. The LR corner will compress only 0.85”, so there will be a slight increase in cross weight for the car that will tighten it off the corners.

An added benefit to this scenario is that if you can make the RR spring compress more and help the RR corner travel more, the right side panhard bar will be lower causing the car to have a lower rear moment center for even more tightness off the corners.

How To Measure Stagger, The Easy Way – Many of you will read this and say, oh, I knew that. Just the same, this is about teaching methods that you may or may not be aware of. This is one trick that I learned years ago and I still see people doing it the hard way.

When measuring stagger, you don’t need to subtract the two measurements to find the stagger amount. You just have to remember one number and that is much easier. If you need to remember tire sizes, just write down that one number.

The magic number is the size of the largest tire for each axle, being the right side for left turning circle track cars. First measure the right side (larger) tire circumference. Remember that number and/or write it down.

Then measure the left side tire for that same end of the car. Let the tape overlap the end of the tape and read from the end where the larger tire size lays on the tape. If the larger tire were 85 1/4 inches and that measurement falls on the 2 3/16 inch mark, then the stagger is 2 3/16”. It’s that simple.

If you remember, or write down the large tire size number for the right side tires, later on if you think you need to swap the right side tires to change the stagger, you’ll know what those tires sizes are for analysis purposes.