Ackermann is important because it can ruin an otherwise great setup. Knowledge of it is important for all types of auto racing, not just circle track. We have readers from all walks of racing life. Recently I talked with a guy who races vintage stock cars on the west coast. The first thing I noticed about his front end was that the older design had a great deal of Ackermann built in. More modern designs incorporate less Ackermann.
Each front steering system has its own particular design and can produce excess Ackermann if not setup correctly.
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 softer front springs, high rebound in the front shocks to hold the car down and stiffer RR 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.
1. The position of the drag link fore and aft has a direct affect on the amount of Ackermann in your steering system. On a rack-and-pinion system, the racks position fore and aft does the same thing. There are other parameters involved in the creation of Ackermann steering effect.
Just What Is Ackermann?
When we have Ackermann effect present in our steering design, it means that the amount of 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 one-sixteenth to one-quarter of an 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 one tenth of a degree. You can imagine my reaction when a racer tells me that they only have a couple of degrees of Ackermann in the car. A degree of Ackermann equals 1/2-inch of toe for an 85-inch circumference tire. So, if we have two 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.
2. This drawing and information depicts why we need some slight amount of Ackermann steering effect. What is shows is that the amount of this effect is slight and in the tenths of degrees and not whole degrees. With this knowledge, we now understand that we can almost eliminate Ackermann from out steering systems.
What Causes Ackermann?
There are several different ways that your car could be producing excessive Ackermann effect. The most common is when we install the wrong spindles or other steering system components on our car.
Over the last few years, teams and car builders have worked hard to reduce the unsprung weight, or the weight of the wheel/spindle assembly. I'm not sure why. One way to accomplish this was to install a lighter spindle.
At first car builders began using smaller, stock compact car spindles on the front ends that were designed for the Drag Link Steering system. At the same time, custom spindles were being fabricated for the newer design and very popular rack-and-pinion steering system.
These later spindles were different in design from the stock spindles because they had steering arms that were pointed straight ahead from the ball joint instead of being angled in from a top view at the tie-rod end like the ones used on the drag link steering systems. This caused a tremendous amount of Ackermann.
Even in systems designed to use the newer spindles, we can have excess Ackermann. The lengths of the steering arms and the position of the rack-and-pinion fore and aft can contribute to producing excess Ackermann.