SpecRacer.com

Robert Mumm wrote:Pat,

We have never really worried about caster to much, and never ran 5 much less 6 degrees over all the different tires and setups, but the smaller front tires may be the reason you need more to load the inside tire.

We had outlined the setup procedures on our website a few decades ago, but still should be good. Look under "Secrets of the Brotherhood" and then hit "Chassis Setup Procedure".

I'm with Robert on this. I increased caster as recommended for the most recent version of Goodyears and didn't like the car at all. I am leaving my caster where it is to start.

You may find the car "pushy" at low caster settings, as well as a bit unsettling down the straights (I suspect that the radial is much more sensitive to toe out.) More caster may help the car feel a bit more stable under those conditions. Run what you'd like, but realize that a lot of test hours went into the recommendations. Remember we also ran close to 5 degrees on camber as well, which the Yokes handles just fine. We are dealing with a softer compound that will wear more than the older tires we used (we're seeing 3+ seconds per lap improvement) so wear will more noticeable. That said, through the years I saw the same tires with radically different setups and the fast guys were, well, the fast guys, no matter what, so go figure...

We will be setting up our car as close as possible to the recommended setup and go from there. That's a starting point and the feedback seems to be that is in the ballpark, that's really all we can ask for, then it's up to us to tune.

After several hours, I finally think I have the car setup where it should be. I can't imagine trying to change the setup at the track without scales. My main concern is the large change in the front caster. I am increasing it by almost 4 degrees. Considering my concern for having to make a change at the track before a race, what can we expect? Has anyone changed their front caster that much and if so how did it feel on the track?

My concern of course is with the steering effort.

Pat

Since Comprent set up my car, I haven't touched a thing except the overall ride height. And that was on advice of Kevin at Comprent, so that the car wouldn't scrape some curbing. I'm very happy with the car. In fact, I find that the car is easier to trail brake in certain situations than the Goodyears were with the old setup. I assume the added caster probably helps in those situations.

goolsbey wrote:After several hours, I finally think I have the car setup where it should be. I can't imagine trying to change the setup at the track without scales. My main concern is the large change in the front caster. I am increasing it by almost 4 degrees. Considering my concern for having to make a change at the track before a race, what can we expect? Has anyone changed their front caster that much and if so how did it feel on the track?

My concern of course is with the steering effort.

Pat

I've used pretty aggressive caster settings (5-7 degrees) on my FF cars and Spec Racers and never really noticed a huge increase in steering effort.

That is what I wanted to hear! We haven't, perhaps we should have considered it. Looking forward to giving it a try. Thanks Bob!

Pat

With the Goodyears, 5 deg of caster resulted in steering effort that was to high for the incipient carpal tunnel in my right wrist, so I went down to 3 deg. With the Hoosiers, I haven't had any issues with 6.5 deg of caster. I think the narrower tire reduces the steering effort significantly. I'm not sure, but perhaps radials require inherently lower steering force too? I'd also suspect that gyroscopic centering forces are lower because of the smaller diameter, but how significant can that be?

I've always liked the faster self-correcting action when counter steering that I get from the higher front caster settings.

Im running the lower end of the recommended set up and I like it so far. I don't think the steering effort is anymore than previous with the goodyears. Still tweaking the sway bars based on how the car is feeling.The suggested setup ranges seem to be working so far.