How to Check for Ackermann Effect

There are a few ways to check for excess Ackermann in our race cars. The best way is to use a laser alignment system to measure how much each front wheel turns and compare the two. The laser system can also be used for rear end alignment, right side tire alignment and bump steer.

A less expensive, but adequately accurate method is to use strings to measure your Ackermann. I have used this method and if done carefully will yield the results we are looking for. Almost everyone has used strings to align a race car. A string pulled tight is always straight, we can count on that.

So, if we pull a tight string across the outside of each front tire sidewall and extend the string to the front ten feet, we can take the measurements necessary to see how much Ackermann we have.

The procedure is as follows: 1) Put the front wheels straight ahead. 2) Pull a string across the outside of each front tire (avoid the lettering portions of the sidewall) and place a mark on the floor (on a piece of masking tape) exactly 10 feet from the spindle pin to mark where straight ahead is. 3) Then turn the steering wheel approximately the same amount the driver would in the turns where you race. 4) Again, make a mark on the floor at 10 feet where the string extends from the outside of each front tire. 5) Measure the distance between each set of marks for each wheel and compare the left wheel with the right wheel.

The Ackermann Toe Chart shows how much toe is gained in relation 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.

3. We can measure Ackermann several ways from using lasers to using a simple string. This shows how we project the direction of each tire out 10 feet in front of the “axle” and measure the amount each wheel turns as the driver steers the normal amount for the track where you run. The two dimensions should be nearly the same for near zero Ackermann.

4. This chart shows how much Ackermann is present in our race car based on the amount of difference in the left and right measurements taken 10 feet out in front of the “axle.” For example, if we read a 1.5 inch difference for tires that average a circumference of 86 inches, the amount of added toe when we steer the wheels is 0.342 inch, or about 11/32-inch.

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 where the driver turns both right and left.

Lengthening the left steering arm will reduce the amount that wheel turns with a measured steering input, which reduces Ackermann effect. The opposite is true for the right steering arm—we would need to shorten it in order to reduce Ackermann. We can also change our drag link to move the inner ends of the tire rods forward to reduce Ackermann or rearward to increase it or to reduce Reverse Ackermann effect. This serves to change the Ackermann in both steering directions.

If your spindles were not designed for your steering system, change to the correct spindle design and possibly have some lightweight ones fabricated to the exact specifications as the correct ones. I did that way back in 1997 with a brand-new car.

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 improving our Ackermann effect in one direction, it must be correct for left or right turning of the wheels with those cars.

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.

If we pull a tight string across the outside of each front tire sidewall and extend the string to the front ten feet, we can take the measurements necessary to see how much Ackermann we have

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Longacre Racing
16892 146th St SE
WA  98272
Intercomp Racing Systems