This photo shows several things...
This photo shows several things about the alignment side of setup. First, it shows us that if the left front tire is off the ground, we needn’t be concerned with Ackermann or toe settings. And, if the rear is steering this much, we probably have moment center issues. In this final installment, we’ll learn how to finalize our setups.
Now that we have covered the goals and methodology of setups in Part 1, and caster, camber, and bumpsteer in Part 2, we now need to finalize our setup guide by examining the final phase of setting up our race cars, and that involves alignment.
This subject includes simple toe settings, Ackermann—which is toe change from steering geometry—rear alignment, and rear steer due to chassis movement. We can refine and perfect those items included in Parts 1 and 2, but if we don't finish out with these last items, all of our hard work will be for naught. We'll end up chasing our bad handling car like so many racers do week in and week out.
So, let's move on to alignment and as in past discussions, we'll do this in a practical order so that later routines don't interfere with our previous work. For instance, if we square the rearend perfectly and then adjust our right-side alignment, we then mess up our rear square. And, if we set toe and then adjust our Ackermann, the toe will change and we'll have to do it all over again. Here goes:
The Ackermann Effect
This effect is important because it can ruin an otherwise great setup. In this day and age, for both the dirt racers and the asphalt teams, modern setups dictate a closer look at many areas of chassis geometry and alignment. If we prioritize the various areas of concern, Ackermann would rank right up there near the top. More importantly now, modern setup trends in both dirt and asphalt racing dictate that we need to take a closer look at our Ackermann situation.
As we have shown before, a...
As we have shown before, a race car on a ½-mile or less sized track needs very little Ackermann so that the front wheels will track along their perspective arc. We’re talking about a fraction of a degree, not whole degrees.
Years ago it was fairly common to see a dirt car with the left front tire up off the track in the turns or see tire temperatures on an asphalt car's left front tire that were the coolest of the four. These were the result of unbalanced setups where the rear suspension desired to roll much more than the front suspension. In those days, greater amounts of Ackermann could be desirable, or at least less harmful to our handling. If the LF tire is off the racing surface it can do no harm.
Ackermann effect is a mechanical phenomenon that is associated with an automobile's steering system. A steering design that incorporates Ackermann causes the inside wheel (closest to the radius of the turn) to turn a greater amount than the outside wheel. We do need a slight difference in steering angle between the front tires because the inside wheel runs on a smaller circle or arc than the outside wheel. The key word here is "slight."
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 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.
To check Ackermann, we can...
To check Ackermann, we can use laser systems or strings. The string method is just as accurate because we are multiplying the effect three or more times. This method is simple and quick, leaving no excuse for not knowing your Ackermann effect amounts.
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 more than 1⁄10 of a degree.
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 rearend alignment, right-side tire alignment, and bumpsteer.
A less expensive, but adequately accurate method is to use strings to measure your Ackermann. I have used this method and, if done carefully, it will yield the results we're 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 10 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) where straight ahead is. 3) 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.