Gator Bait

Yet another alignment settings thread... I'm currently running the FM settings (that they dialed in). Just from looking at my (new) rear tires (225/45/15 RS3) I'm not using the entire available contact patch. I was thinking about reducing rear camber but by how much? I was also considering slightly lowering the rear to near zero rake.

Anyone play around with settings with an eye on straight line traction? For clarity, this is for roll racing...third gear, 60 mph hits through 150 or so. ..not drag racing from a dig. ...also b4 the lectures start, this is done on closed circuits. (i.e. Runway Rivalry in Dallas - May 18, 2014 - LS1TECH )

And of course mounting up some 40 wear DOTs on a spare set of wheels is an option, but I'd like to maximize the current available traction. TIA

.boB

The best way to set alignment is with tire temps. A probe type thermometer will be the most accurate, but an infrared will work.

For best straight line traction, you'd want the same temps across the tread. that would be perfect alignment and pressure.

But for stability, you would want a slight bias to the inside of the tire.

For my Cobra (with IRS), I use 0.25*. That seems to give the best balance on traction and stability. Gives me a real even temp across the tread, too.

Gator Bait

I've been wanting to add an infrared to my tool box for multiple uses. This may be a good excuse. How would you suggest testing? Make a couple of test pulls then immediately read temp center and edges?

I was thinking of a less scientific approach..adjust...test...adjust...test... But like the idea of a more objective method.

.boB

That's pretty much it. Start with a good base line, then test and adjust. I collected a lot of tire data over the years getting the right settings.

charchri4

Bob are you saying you run a 1/4 degree of positive camber on your Cobra? That is a jaw dropping number for sure if that's the case. I've been running -1.6 and was thinking of dialing it back but can't imagine going that far. Positive camber really? What do you run in the front?

Aligning it tonight...


Wow Gator that looks like fun! Not much of a drivers game though...

Gator Bait

I would differ on the driver aspect. Consider this...every road (circuit) race begins and ends with a drag race. There are skills brought to bear for certain.

GoKart

If the car is build for straight line traction only, slight positive camber makes since. Under acceleration the car will squat which causes you to gain negative camber resulting in somewhere near 0 camber.

Last year, in an attempt to get some use of 1st gear, I ran a pair of MT drag radials on the rear. Due to the amount of camber/toe I was running, they lasted approximately 800 street miles.....

I recently had the rear set to about 1.5* camber and a very slight toe in and added a pair of adjustable rear upper control arms. With these you can set your rear camber to what you want for an event, then accurately change it back to where it was when you're done.

.boB

No, negative camber. I can't think of a good reason to ever run positive camber on a street car. And only occasionally/rarely on a race car.

tbone heller

I have been running 0* camber & toe in the rear with good results.

charchri4

I was thinking I could take it down to -.05 or so and try it for a while but I can't get it there. With both adjustors all the way inboard I'm at -1.4 and when I back the rear ones off a bit to set the toe I'm at -1.8. So I guess my 200,000 mile bushings are not so good anymore.

GoKart

Depending on your ride height, -.5 camber might not be achievable.

charchri4

Oh dear I didn't know that. I may have boxed myself into a corner here then. I'm running 25" tall tires with the suspension lowered to make up some of the difference. So to the alignment bolts it's pretty low but for ground clearance it's really not.

Seemed like a good idea at the time!

GoKart

Yeah, the lower you have your suspension, the more difficult it will be to run a smaller amount of camber. That's why I ended up with the adjustable rear uppers. Just not enough adjustment in the eccentrics.

.boB

If you've lowered the car so much that you can't obtain the proper alignment settings, it's too low. The suspension isn't designed to work that way, and you essentially changed the pick up points.

Especially in the front. The lowered height can really change things like bump steer, caster, and weight jacking. By changing the angle of the lower arms, you can adversly effect the roll center and roll couple.

By raising the ride height as little as 1/2", you might find the car handles better.