One of the critical elements of proper chassis alignment is the steering system. The front wheels must work together, just like the two ends of the car, so that they can produce the greatest amount of traction to turn the car. This area of chassis setup falls under the umbrella of those systems on our cars that can ruin an otherwise great setup if not designed correctly.
We have published previous stories about Ackermann, its definition and technical details about why it's important. However, we have learned more about this important subject. We need to continually consider Ackermann and how it affects our overall chassis setup package.
To measure toe, measure between...
To measure toe, measure between the front of the tires and the rear of the tires and subtract. This car has toe-out, meaning the front of the tires are wider than the rear. If we subtract the rear (8011/48 inches) from the front (8031/48 inches), we see that this car has 11/44 inch of toe-out.
What is Ackermann Effect?
Ackermann effect is a phenomenon associated with an automobile's steering system. A steering design that incorporates Ackermann causes the inside (closest to the radius of the turn) wheel to turn a greater amount than the outside wheel. We need this difference in steering angle because the inside wheel runs on a smaller circle or arc than the outside wheel.
Ackermann effect is named after the man, Rudolf Ackermann, who discovered and did research and development on the subject. Early in basic automotive design and development, engineers discovered the need to design an exact system for steering a production car so that each wheel tracked correctly when the car was negotiating a turn. The ideal system would compensate for large radius turns as well as for tight, "turn right at the stop sign," type of smaller radius turns.
History offers that many of the very first owners of automobiles were concerned about tearing up their circular gravel driveways, and the Ackermann designed into the car helped keep the wheels tracking correctly and reduced the primary cause of rutting in the driveways.
In a recent study for a Circle...
In a recent study for a Circle Track article, we did some serious calculations using an accurate coordinate geometry software program to see just how much Ackermann is needed. The results indicate that we do not need whole degrees of Ackermann, but decimals of degrees.
Do We Need Ackermann in Our Race Cars?
There have been many opinions about the use of Ackermann in our race cars and whether it really helps. Numerous older books and articles on the subject extol the benefits of Ackermann to help the car to turn. Are these articles correct? The answer is yes and no. Here is why.
In our past, going back some 30 years, the suspension and steering systems in oval track stock cars were strictly stock units that exhibited characteristics of the intended use-to drive around the neighborhood and down the interstate. Converting the car to circle track racing was beyond its original intended use. It is easy to understand why some of the systems may not have worked well on the racetrack.
Early crewchiefs did not understand, nor did they have the technical knowledge to develop what we now know as a balanced setup. This is where the suspension systems are working together and doing the same thing when the car is in the turns. This balance makes a lot of good things happen, such as causing all four tires to work hard and providing consistency in the handling balance between tight and loose.
Because most cars were not properly balanced-although some did get there through trial-and-error guessing-the left-front tire usually did little work. This was evidenced by several indicators: 1. cool left-front (LF) tire temperatures compared to the left-rear (LR) tire; 2. a need for a stiff right-front (RF) spring, as the RF corner supported most of the front load off the car in the turns; and 3. excess RF tire wear and heat. If the LF tire had little weight on it in the turns, then teams learned that excess Ackermann actually helped the tire to generate more heat and turning effort.