The inner tie rod ends move...
The inner tie rod ends move forward with the drag link; 5. The outer tie rod ends (at the forward ends of the steering arms) are forced wider apart as both tie rods become less angled from a top view, creating additional toe-out. The angled steering arms produce a Reverse Ackermann effect which serves to cancel the system's attempt to spread out the wheels. So, the system shown can produce very little Ackermann effect.
A drag-link system is correctly designed with angled steering arms. The system inside the steering arms will produce unwanted Ackermann effect, which needs to be canceled. The result of turning the steering wheel is as follows: 1. The driver turns the steering wheel left; 2. The drag link moves to the left; 3. The drag link moves forward as the Pitman arm and the idler arm rotate around fixed points; 4.
So, when we hear older, more experienced crewchiefs tell us that using higher levels of Ackermann really helps their race cars to turn better, we can believe them. Now that we have learned how to properly balance the car, we do not need the excess Ackermann in our steering systems. In fact, if we do not remove the excess Ackermann effect, it will have a reverse effect on our handling and actually make the car develop a push as the two front tires fight each other to go in different directions.
When we have Ackermann effect present in our steering design, the toe is increased. Conversely, with Reverse Ackermann, toe is reduced when we turn the steering wheel. There are many different static settings for frontend 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 frontend and keep it from wandering back and forth across the track. Conventional wisdom tells us the car will need more static toe-out for the smaller radius tracks. At racetracks of more than a half-mile, less toe-out is required. The amount of toe-out used typically ranges from 11/416 to 11/48 inch.
The stock spindles with the...
The stock spindles with the steering arms angled (when viewed from the top) were intended to be used on the stock-based drag link steering systems. When racers started using the lightweight rack steering arms on the drag link system, it produced a considerable amount of Ackermann effect and caused a gain of toe when the steering wheel was turned.
The rack-and-pinion steering system is designed to use straight-ahead steering arms and produces very little Ackermann effect if both arms are the same length. Since both wheels turn the same amount as the rack moves back and forth, the wheels steer an equal number of degrees.
Regardless of the amount of static toe-out you use, the toe numbers can be very different as we turn the steering wheel. If our car gains toe when it is steered, commonly referred to as toe-steer, then we have Ackermann effect. If our car loses toe when it is steered, we have Reverse Ackermann effect.
We need very little Ackermann effect in most situations when racing on an oval track. Even on very tight quarter-mile tracks, the LF wheel will only need an additional 11/416 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 he or she only has a couple of degrees of Ackermann in the car. A degree of Ackermann equals 11/42 inch of toe for an 85-inch circumference tire. So, if we have 2 degrees of Ackermann in our steering systems, that equates to 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 this points to the fact that we all need a correctly designed steering system, most racers and many car builders still do not fully understand the steering systems in their cars and how they work to produce or cancel Ackermann.
What causes Ackermann?
There are several ways that your car can produce Ackermann effect. The most common is by installing the wrong spindles or other steering system components on the car.
You can't use rack spindles...
You can't use rack spindles on a drag link steering system, and you don't want to mount drag link spindles on a rack system. Doing this would produce a considerable amount of Reverse Ackermann, or toe loss.
Over the last few years, teams and car builders have worked hard to reduce unsprung weight-the weight of the wheel/spindle assembly. One way to accomplish this was to install a lighter spindle.
At first, car builders began using smaller, compact car spindles on the stock frontends of full-sized cars that were designed with the drag link steering system. At the same time, custom spindles were being fabricated for the newer design and 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.
In the mid-'90s, some car builders swapped the heavy cast-iron stock car spindles that had been used with their stock-based drag link systems for the lighter "rack" spindles intended to be used on the rack system. The result was a steering system that produced excess Ackermann effect. This hurt the turning performance on those cars.