This chart will help you determine...
This chart will help you determine how much added toe you’re getting when you turn your steering wheel at mid-turn. This is based on measuring the steering amounts 10 feet in front of the center of the wheels and for each tire circumference. Toe gain of 0.125 or more is excessive for most tracks.
The Ackermann Toe Chart shows how much toe gain relates to differences in the left and right wheel measurements for different size tires. We can average the left and right tire sizes and look at that number when finding our Ackermann on the chart. Remember that if the left wheel moves farther than the right wheel, then we have Ackermann, or toe gain. If the right wheel moves more than the left wheel then you have Reverse Ackermann or loss of toe.
Solving the Excess Ackermann Problem
If your car gains or loses toe, there are a couple of ways to correct the situation. You can adjust the length of one or both of your steering arms to compensate for Ackermann effect. This works best for a car where the steering wheel is always turned to the left as opposed to a dirt car that sometimes has the wheels turned to the right too.
Lengthening the left steering arm, and/or shortening the right steering arm will reduce the Ackermann effect. We can also change the position of our drag link to move the inner ends of the tire rods forward to reduce Ackermann or rearward to increase it.
To regulate the amount of...
To regulate the amount of Ackermann in a rack steering system, we can move the rack fore or aft to compensate for the widening of the tie-rod ends when we steer the car right and left. When the tie rods are more parallel from a top view, there is less Ackermann. This method of adjustment works best for dirt cars that turn both right and left.
For a rack-and-pinion steering system, moving the rack forward in relation to the outer tie-rod ends will reduce Ackermann. Most Dirt Late Model cars use the rack systems, so we don't have the convenience of only having to improve our Ackermann effect in one direction, it must be correct for left or right turning of the wheels.
Asphalt Late Model cars are also designed with rack systems. Instead of changing the length of the steering arms, it might be best to move the rack and keep equal length steering arms when working to reduce excess Ackermann.
Make sure you know how much each of your tires are steering and reduce the Ackermann effect if needed. Then, when you balance your setup, both front tires will be working in perfect alignment to steer your car. A good steering race car is one that will have more turning power and is therefore more capable of running up front and winning races.
Adjusting Rear Steer
Before we align the entire car, we need to address the issue of rear steer. Making adjustments for rear steer will affect our alignment, so we do those first before we align the car.
Rear steer is caused by the...
Rear steer is caused by the motion of the rear portion of the chassis in dive and roll where the rear links cause movement of both the rearend, and rear wheels, to the front or back. A system can be designed for minimum rear steer, or a calculated degree of steer if that is what is desired. It’s the angles of the links that determine the degree of steer.
How we design and place our rear trailing links has a lot to do with how our car will handle. As the car moves vertically and rolls, the rearend will most likely steer to a certain degree depending on the design. Rear steer design goals are very different between dirt cars and asphalt cars.
On asphalt, we can only tolerate a very small amount of rear steer and most of the time we are better off with close to zero rear steer. On dirt, some teams incorporate lots of rear steer to the right into the suspension. The degree of steer is directly proportional to the amount and direction of vertical movement associated with the right and left rear suspension systems.
We can simulate the degree and direction of rear steer in our race cars by duplicating the movement of the rear suspension. If we take visual reference to the position of the wheels in the wheelwells during cornering, we can get sufficiently close to replicating the suspension attitude of the car in the shop.
We could then support the chassis at levels similar to the way the car looks on the racetrack and then measure how far each rear wheel moved and in what direction. It may surprise many how far the rearend steers under some conditions.
If more or less steer is desired, changes can be made to trailing arm angles, and so on as you're simulating the rear steer and the results can be measured. This is an excellent way to learn how arm angle changes relate to rear steer magnitude.