So, it might be more correct to measure bumpsteer at three to four inches of bump rather than at normal ride height. If you go from normal ride height all the way to full bump, we need to know if the wheels are steering in that amount of travel.
What we might find is that we can't achieve near zero bumpsteer, but we can mitigate it, meaning we can utilize its motion to get what we want. Basically, we want the front wheels direction in relation to each other to be the same at mid-turn bump attitude as it was at normal ride height, even if it moves off of that in between static and full bump. If your car runs on bumps, this will be correct for that application.
If each wheel steers say twelve degrees either in or out in four inches of bump, if you adjust your tie rod angles so that the right front steers out, and the left front steers in toward centerline, then all the driver needs to do is steer that little bit more to compensate and it is a natural motion that he won't realize he needed to do. And, the two wheels will be pointed so that the toe-out won't change.
A more correct way to check for bumpsteer is to turn the wheels in the direction and amount they will be pointed at mid-turn and do your bumpsteer check there. This is where we need to know how much bumpsteer we will be experiencing. Remember that the geometry of the parts (arm angles, tie rod angles, and so on) all change when the chassis dives and rolls in the turns.
Step 5—Ackermann check. We need to know if both front wheels are pointed in a more parallel direction when we steer the car. On asphalt, we are mostly concerned with left turns, but on dirt, we will be turning both right and left most of the time.
We have proven that for short tracks of from a quarter mile to a half mile in length, we need tenths of degrees of Ackermann, not whole degrees. If your front wheels gain a degree of toe at normal steering input, that produces an additional half inch of toe. We certainly don't need that.
You can use strings or lasers to check for Ackermann. Turn plates, because of how the tires will move laterally when they are turned, might not produce the required accuracy that would show how much Ackermann you have. You can do both (stringing and turn plates) and if they agree, then you can continue to use the turn plates.
To adjust your Ackermann, you can adjust the steering arm lengths for asphalt applications (remember we are only concerned with turning left), but for dirt, we need to adjust the drag link position fore and aft, or the rack-and-pinion fore and aft until we get near zero Ackermann. That will reduce Ackermann in both steering directions.
When you get done with the Ackermann check, reset your toe-out, it will have changed. It also gives your team practice in doing the toe check. Use the same two people, if possible, for each check. Use one tape, or compare two tapes to each other if you use two, to make sure they agree.
Step 6—Once the front end is aligned, we need to go to the rear and check for rear steer. We have already aligned the rearend in the static position, but that is not necessarily where it will be pointed while going through the turns. And modern setups have changed as to the amount of motion of the rear of the car in many cases and that affects the rear steer.
With the move toward stiffer right rear springs for both asphalt cars and dirt cars, the amount of RR movement has been reduced. If, back in the day, you ran a 175 lb/in spring in the RR, and you are now running a 350 lb/in spring, the shock travel would be half of what it used to be. Therefore, the fore and aft movement of the rear wheels created by the trailing arm angles will be different. How much different and in what direction is what you need to find out.
With the chassis on jack stands, and the springs removed, move the rearend through a simulated travel that will represent its position and movement on the racetrack from straightaway configuration to mid-turn compression. If you install just the shocks, you can mimic the shock movement that the indicators show after running the car.
Measure accurately the movement of each rear wheel in the fore and aft direction using whatever method you choose. With the wheels removed, you can string down to the floor off the front or back of the axle hubs, the center of the hubs, or you can string along the tire to a point well away from the axle centerline.
I usually will hook a tape onto the rear of each wheel rim and run the tape to the front, parallel to the ground to a mark on a tape near the front wheel well. Take a measurement at each point of travel. Whatever method you use, there should be very little steering of the rear axle through the normal travel range.
For most rear suspensions, there will be some amount of steering. The goal is to end up at mid-turn travel with the same alignment as you had at static ride height position, or whatever steer you choose to create. For teams who have studied this and have refined their rear steer requirements, the goals might be different than what I have stated.
Again, there are specific steps to follow with each of the above stated routines. Follow your manufactures suggestions for each product used to measure each area of the car, or go to our website and read the many articles that deal in detail with each step.
So, we have set all of our caster and camber, wheel toe, aligned the front and rear wheels, checked for front and rear bumpsteer and made corrections to simulate the wheel travel we will experience on the racetrack.
This part is the first presented because, before you even think about springs, shocks, and sway bars or load distribution, you needed to check and refine your alignment. Many top teams will go through all of this periodically, even if nothing seems to have happened to the car to change it.
If you have specific questions about your particular application related to alignment, write to me or ask your fellow competitor or a tech representative who works with racers in your division. The manufacturers of the equipment used for these measurements have printed or online instructions and procedures that you can refer to.
Remember that the geometry of the parts (arm angles, tie rod angles, and so on) all change when the chassis dives and rolls in the turns