Tire Stagger for a Road Course

[sopwith21]

We tried something last week that worked pretty well and I wanted to see if any of you guys had ever tried the same thing... we staggered our tires and strut settings for right hand turns.

9 of the 11 turns on the course were right handers, so we measured the tires and found 1.75" of available stagger. Since the diff on my car is welded, I figured we could use it. So we put the largest tire on the LR, next largest on the RR, next largest on the LF, and smallest on the RF.

Then, in a series of practice sessions, we tested different strut settings (I've got Tokico 5-way adjustables on all corners). We started with the front and found that a pretty stiff setting (4) was just right and kept the nose stable without diving in the corners. Then we worked the rears from 4, down to 3, then 2 and 1. We found that 2 was the softest setting we could use (softer in the back gives more grip, which we needed because of the welded diff). That tightened the car up and gave us far better grip off the corners under throttle. We then stiffened the RR strut back to 3, to transfer a bit more weight to the outside rear tire in all right hand corners. Man, did the car ever fly through the fast right handers after that!

We had already set our coilovers and ride height and were satisfied with it, so the only thing left to manipulate was tire pressure. We made some changes there but the car didn't notice the difference that much. The struts and the stagger were what did the trick.

We were so busy testing that we just tested right through qualifying without ever trying to make THE hot lap. We still qualified third of twenty and went on to win our class and the overall race with ease. I was super happy... not just with the win, but with the way the car responded and our progress in practice.

I've come to believe that so long as we have the welded diff, the car will always be a bit loose no matter what we do. However, the car now bites far better off the corners and we only get the tiniest push only in very tight corners going in, and it is manageable. We noticed after adding the stagger that the car just plain flies through the high speed corners. The difference was amazing.

Does anyone else do this, and were your results as good as ours?

[Phred]

Sopwith21,

I raced in SCCA for eighteen years in H-Prod, Spec Racer, Gt-3, Gt-4, and a few enduros in Sports racers. I am now a crew chief on a USAC Midget. These cars are animals. All up race weight is 950 lbs, with 350 horsepower. The power to weight ratio is much better than a formula atlantic car. And the're only designed and tuned to turn left. I wish I would have known in my road racing days, what I have learned in Midgets. That is, how to tune stagger and shocks for handling. Just for reference, a midget runs about three and a half inches of stagger in the rear. If we have trouble hooking up the rear on exit, we'll soften the RR spring, and or, sway bar, and or, decrease front rebound resistance to transfer weight to the rear. Also you can adjust stagger with pressure changes without effecting the tires ability to grip, as long as you stay within the tires working temp. range. Sure, you might not have perfect temps across the width of the tire, but sometimes stagger is more important. We test much more now than when we were roadracing, because there are more areas to tune to make a car turn left, than there were to make a car turn both ways. I'm still a roadracer at heart, but this type of racing is very exciting, and very challanging to tune the car. Summary: don't be afraid to try new things, keep good notes, and always try to make the car better, even if other people think you're a staggering drunk.

Phred

[sopwith21]

Yup... I'm hearing ya. I'm from Indy, so of course, for the first ten years or so of my driving career I was solely on ovals.

Last Sunday morning during practice, I told our crew chief to take off the tires and measure them, then stagger them. He wasn't too happy about it since he had just torqued the wheels down... but I knew no one had staggered the car properly so I insisted. 1.75" of potential stagger is just too much to not have an effect. So they swapped the rear wheels and quit.

I had to jump in and measure the fronts and move them around myself... my road racing crew apparently didn't realize the effect that the front stagger has on the car's crossweight in the corners (what you would call "wedge" on your circle track cars).

Two sessions later, we were taking tire temps and noticed that they were very even all the way around, indicating that the car was riding better in 9 of the 11 corners.

Further, the tires had grown exactly 5 lbs each, except for the outside front tire, which grew 6 lbs. That is absolutely PERFECT. All tire temps consistent and nearly equal tire pressure growth on every corner. That's equal pressure on every corner of the car. We lost nothing in the two left handers and were flying through all 9 right handers.

One of the new guys on my crew - a lifelong road racer - had never heard of staggering tires. But if your tires aren't right, everything else you do is just putting a band-aid on a broken arm. All of your other adjustments are fighting the tires, which have the car trying to turn the wrong way.

Did you - or anyone else - ever try this on a road course before? BTW... love USAC racing. Good stuff.