I received another set of questions from a listener this past week or so. These were about a dirt race car that he had just purchased and wondered about turning the front stub and the length of pull bar. Turning the stubs to lead the right front was a hot topic of conversation several years ago, but has died down in recent years. I searched into this topic. I’ve talked to engineers about this; and I’ve done some testing with this. This is what I’ve found out.
First turning the stub and leading the right front tire ahead of the left front will help the car turn into the corner better, especially on the gas. The drawback seems to be that it will hold the car on the right front longer and hurt traction off the corner. Over the years I have made changes to race cars and looked to drivers to leave feedback. This ended up being one change to the car that drivers could really feel. Its usability really depends on the type of track you run on and what your driver wants in the car. When Dan Schlieper drove our cars here at Wild Incorporated, he won a race during Speed Weeks at Volusia, where every day I pulled the right front further forward. He loved how the car turned into the corner on the gas, but we were seeing how the car lacked traction off the corner unless he could catch some moisture on the way out. He won that race on a slide job over Darrell Lanigan, where he did catch enough moisture on the way out to make up for the loss of traction. The track conditions, Dan’s driving style, and car set up all came together. The rest of the week we struggled to repeat that victory because the track changed up where we needed the traction off the corner, and I never pulled the right front back. By the time I did pull it back it was too late in the week.
I do think twisting the stub on a modified and pulling the right front ahead on a late model do two totally different things, but I believe it gives the drive a very similar feeling. On a modified the amount of traction lost off the corner is not as drastic because twisting the stub will pull the right front back under compression, because of having more angle on the lower control arm.
On Schliepers car, I slid the right front forward and still kept it parallel to the center line of the car. This did alter some front end settings, like Ackerman, but at the time everything was coming together and it produced a win. Would I do it again? I would in a certain specific situation maybe. But, as a general rule of thumb, no. There are too many adjustments that can be made on the car to “crutch” a car for certain situations. My rule of thumb is keeping simple and sticking to basics is almost always the best way to go. The basics are difficult enough to keep track of without mixing in a bunch of trick “crutches”.
The length of the pull bar is a common question it seems. Basically the rule of thumb for pull bar length is: the longer the pull bar the more gradual the traction comes on and the further down the straight the traction is maintained. The shorter the pull bar the more instantaneous the traction, but it will run out sooner and unload the traction in the car. That’s the basics. You could possibly tune the drive ability of the car with the length of the pull bar. If you were to consistently run on big tracks with long straights, I would put a longer pull rod in to maintain the traction all the way down the chute. On stop and go, little quarter mile bull rings, a shorter bar will help you pull off the corner harder.
Driving style also has a lot to do with pull bar length. Some people like to race off the corners; some like to race on the way in. You need to keep this in mind when determining the length of the pull rod. If you have a four link car and want to run a long pull bar, you will be more likely to pull the left front tire off the ground because you are picking up further forward.
Another important aspect to keep in mind is that length and angle works hand in hand. Angle will basically determine anti-squat. On a shorter pull bar you can get more angle, but the angle will lessen faster as the back end of the car lifts. The longer bar does not have the potential to get as much angle, but the angle will stay in longer.
There are way too many factors that go into the design of a suspension to say that something in particular is good or bad. Everything revolves around having a neutral balance on the car. Some things work for one car and driver and not another. The best scenario is to learn a much about your car as you can and experiment with your driving to get everything balanced where you need it.
Till next time, stay warm.