Steering System And Suspension - Ackermann Technology - Chassis Tech

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 original intended use, primarily driving around the neighborhood. Converting the car to circle track racing was beyond its original intended use. So, it's easy to understand why some of the stock systems may not work very well on the racetrack.

Early crew chiefs didn't understand, nor had the technical knowledge to develop what we now know as a balanced setup. This is where, as we have explained many times in CT articles, both of 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 including helping all four tires to work harder, and providing consistency in the handling balance between tight and loose.

Since many cars in the past were not properly balanced, the left front tire usually carried less loading and did little work. This was evidenced by several indicators: 1) cool LF tire temperatures compared to the LR tire, 2) a need for a very stiff RF spring as the RF corner took most of the front load of the car in the turns, 3) Excess RF tire wear and heat, and for dirt, a LF tire that had no contact with the racing surface much of the time. If the LF tire had little or no load on it in the turns, then teams discovered that excess Ackermann actually helped the tire to generate more heat and turning effort when it was in contact with the track.

Modern Day Trends in Setup In today's racing world, the dirt cars are more balanced in their setups and the LF tire does much more work. This trend has made the dirt cars more consistent and faster under most conditions. With the asphalt teams, we see a move toward larger sway bars, softer springs, and stiffer LR springs. This arrangement causes the LF tire to be much more in contact with the racing surface, carry more loading, and to work harder than ever before. If the front tires don't track exactly where they should, there will be problems getting the car to turn.

When we have Ackermann effect present in our steering design, it means that the toe-out increases as the steering wheel is turned and with reverse Ackermann, toe is reduced. There are different static settings for front end toe that are dependent on the size of the racetrack, the banking angle, and the type of tire used. Most short track stock car teams use toe-out to stabilize the front end and keep it from darting back and forth across the track. Conventional wisdom tells us that the car will need more static toe-out for the smaller radius tracks. At big racetracks of more than a half-mile, less toe-out is required. The amount of toe-out used typically ranges from 1/16- to 1/4-inch.

The truth is, we need very little Ackermann effect in most situations when racing on an oval track, be it dirt or asphalt racing. Even on very tight quarter-mile tracks, the LF wheel will only need an additional 1/16-inch of toe over the RF wheel to correctly follow its smaller radius arc. That is 0.112 degrees or a little over 1/10 of a degree. You can imagine my reaction when a racer tells me that he or she only has a couple of degrees of Ackermann in the car. A degree of Ackermann equals a 1/2 inch of toe for an 85-inch circumference tire. So, if we have 2 degrees of Ackermann in our steering systems that would equal an additional inch of toe when we turn the steering wheel. We would never think of setting an inch of static toe in our cars and then go racing.

While all of this points to the fact that we all need a correctly designed steering system, many racers and car builders may not fully understand the steering systems in their cars and how they work to produce or cancel Ackermann. Here is an explanation of how it works.