Race Car Set Up - A Baker's Dozen - Feature Tech

Written by on September 1, 1999 13 Cheap Setup Tricks
Race Car Set Up - A Baker's Dozen - Feature Tech View All 16 Photos
Ctrp 9909 02 Z+race Car Set Up+checking Toe 1/16

Race car setup is a crucial aspect of success on the track. But some of the tools, such as scales and laser alignment equipment, are very expensive. One solution is to get a group of racers together to share equipment, or borrow equipment when you can. But the reality is that you can get 99 percent of the work done with some basic equipment. For less than $100, you can get your car set up, then all you really need is a tire pyrometer (as low as $99) and a stopwatch. Here's what you need:

* Machinist's Rule
* Plumb Bob
* Level
* Angle Finder
* Tape Measure
* Angle Iron Or Plate (Steel Or Aluminum)

1 Check Toe With String
A roll of survey string--available at any hardware store--is all you need to quickly check front toe. The string must be held so that it passes around the outside of the rear tire and touches both the front and rear sidewall bulges at axle height. Unroll the string and, with the string taut, slowly move the string until it just touches either the front or rear sidewall bulge, again at axle height. Measure the gap with a machinist's rule at the end not touching the sidewall. The measurement is the toe-out if the gap is at the rear and toe-in if the gap is at the front. If the string does not contact both the front and rear bulge of the rear-tire sidewall, either the rear axle is offset or it is out of alignment. Keep in mind that this method will not work on race cars in which the rear track width varies more than 1 inch from the front track width.

2 Check Front And Rear Toe With Plumb Bobs
Refer to the illustrations. First, put a true scribe mark around the tire. Then place a piece of 1-inch masking tape on the floor where the plumb bobs will touch. Next, lay string with plumb bobs accurately over the scribe line so the tips of the plumb bobs just clear the floor. Let the plumb bobs stabilize, and carefully mark the floor where the plumb bobs come to rest. Do this on both sides, and use a tape measure to measure between the marks. This is a very accurate way to measure toe if the scribe lines are accurate.

An even more accurate way to do this is to use 24-inch-long aluminum- or steel-angle iron. Carefully notch each end for the plumb bob string so the notch is in exactly the same location at each end. Mount the angle iron to the brake rotor with either reversed lug nuts or clamps, and level the angle iron. Mark the floor where the plumb bobs come to rest as above and repeat on the opposite side. Take measurements on the floor between the marks. You can also use this method to check rear-axle-housing toe.

3 Square The Box
The box formed by the steering arm, idler arm, and drag link must be square to avoid unwanted bumpsteer. The distance between pivot points of the steering must be measured accurately. Center the steering by rolling the car forward at least one full tire revolution. Measure between the steering arm and idler arm pivots at the end at the drag link. They should be identical. Adjust if needed. Then measure the diagonals. They should also be equal. If the distance between pivots is equal, but the diagonals are unequal, something is bent. Take a closer look.

4 Bumpsteer
Bumpsteer is toe change during vertical wheel travel. You can use the same setup as in No. 2 to measure bumpsteer. Just disconnect the spring and shock (with the chassis on stands) and use a jack to raise and lower the suspension. Start with the suspension at ride height and mark your piece of tape. This is your baseline. As you raise and lower the suspension, the marks will usually move inward with zero bumpsteer. If one end moves farther from the baseline than the other end, bumpsteer is present. The difference in measurements is the amount of bumpsteer. If the front measurement is bigger, you have toe-out; if the rear is bigger, you have toe-in. Plot the change at 1-inch increments for 3 inches of bump and 3 inches of rebound travel at each front wheel.

5 Caster
Use an angle finder on a vertical location on the front spindles. This may not be completely accurate for actual caster angle, but you really want to know the amount of caster split, and this is a very good way to measure that.

6 Camber
Camber should really be set by tire temps, so knowing a camber angle in advance is not important. But once you get the tire temps right, you need to know the camber angle so you can repeat the setup at that track. Make sure the car is on level ground before measuring. You can use a straightedge against the tire with an angle finder (be sure to avoid the raised letters on the sidewall), or place the angle finder on the upper control arm. Its angle is directly related to the camber angle at that wheel.

7 Panhard Bar Setting
Use either an angle finder on the Panhard bar for an angle, or scribe a line around the adjuster on the slider tube (if you have one), and use that as your baseline. A machinist's rule can then be used to measure above or below the baseline.

8 Crossweight
While scales are the easiest way to do this, the crossweight is determined by ride heights. Change a ride height and the crossweight changes. If you do not have access to scales for a baseline, set the rear ride height to the chassis builder's specs, or level side to side. Set the front slightly lower but also level side to side. At the track you can tune the chassis, but change ride heights in very small amounts a half to a full turn while trying to keep any single corner of the chassis from getting too high or low. Keep notes and do this until the car handles the way you want. Recheck the ride heights, and now you have a setup that works. It is a lot more time-consuming, but you don't need scales to get there.

9 Rear-Axle Alignment
A simple tape measure is all you need. Measure from a lateral framerail forward from the axle housing to the rear-axle housing. The trick is finding a spot on each side of the housing that is square. Better yet, drop a plumb bob from the hub on the axle centerline on each side, and draw a line through each mark. Measure from the line to an identical spot on the left and right sides of the lateral framerail. Now you have a very accurate measurement. The rear-axle housing is out of alignment if the measurements are not identical.

10 Brake BiasBrake bias is best set on the track with an observer watching for wheel lockup at one end of the car first. Just use old tires. You can get in the ballpark with a torque wrench. With the car on stands, have someone apply the brakes until one end locks up. Use the torque wrench on a wheel lug, and measure the torque it takes to turn the wheel. Apply more pressure until the other end just locks up. Check the torque at the first end again. The front should lock up first; due to weight transfer, the front should require some amount of torque higher than the rear. Asphalt needs more front bias than dirt. Test the bias on the straightaway with an observer before you run at speed on the track.

11 Scaling
You need to know what your car weighs and what the corner weighs. If you don't have scales, try to use the track scales, or borrow old grain scales. If all else fails, use local official truck scales so you have a place to start.

12 Rear-End Trueness
It is important to know if the rear-axle housing is straight, or has camber and/or toe. We checked toe in No. 2. Use the angle finder on the brake rotor for camber. Be sure the car is level on jackstands. A little toe-in is OK, up to 18 inch. A little negative camber is OK, up to 316 inch. More of either, or any toe-out or positive camber, requires that the rear-axle housing be straightened.

13 Wheel And Brake Rotor Runout
Clamp a scribe or pointed punch to a weighted (for stability) jackstand. Place the end of the scribe against the wheel rim at the bead or against a brake rotor. Rotate the wheel or rotor until you find the high spot, and position the scribe. Rotate the wheel or rotor until you find the low spot, and use a machinist's rule to measure the gap. That is the amount of runout. Check with the wheel or rotor manufacturer about runout tolerances. Too much wheel runout will have an effect similar to bumpsteer, and rotor runout will cause brake pad kickback, which you can often feel in the brake pedal under hard braking. Rotor runout hurts braking performance.

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