I did some searches and came up dry. How would you go about dial in the proper amount of negative camber in the rear; specifically for autox? I like the car to rotate, so having too much rear camber may be counter productive. What should I be looking for when dialing in rear camber?

Thanks in advance.

oe

 

Depends on front camber. Rear should be about half of front.

 

Positive Caster: 4-6° (if you can get it)
Front: -2° Camber; 1 mm toe OUT (total, so 0.5mm each side)
Rear: -1.2° Camber; 1 mm toe IN (total)

Also, have the rear diff plates restacked per the factory manual (one is 'flipped' in the US model).

 

all depends on the rest of your setup. spring rate, sway bars, tires used, tire size, ect. there are many ways to control rear grip, not just camber.

 

Autocross is all about setting the car up per class rules. What class will you be running in?

The amount of camber needed will vary on 100 different things. Need to take tire temps to really figure out the optimal setting.

 

The car is in STU trim. I was asking in terms of how do you go about adjusting rear camber to give the maximum grip while still allowing good rotation. I know people have specific numbers to recommend, but I'm more interested in the actual process. Like what kind of tests you can do (tire temp), what kind of drills you should drive (figure eights, slaloms and etc) to really help me feel the effects more rear camber is giving me.

Should you sacrifice maximum rear grip for some rotation?

For example, I'm running 700Lbs rear springs on JRZ RS Pro with a Robispec rear bar at 3rd stiffest setting. About -1.5 deg of camber, and a little bit of toe out. It would seem the car rotates well, but I want more. The car seems neutral in most elements. In fast (top of second gear) slaloms the rear seems to float, and car starts to feel dicey.

So maybe a little bit more rear camber to keep the car more planted? Thoughts?

 

I don't think you want to give up grip to achieve balance. Optimize the camber based on your tire temps. Then use sway bars, springs, and shocks to adjust balance.

 

After 7 autocross events, I noticed the outer half of my rear tires were wearing faster. I added more negative camber as a result. Just some trial and error. (-3 up front and -2 in the back on my talon)


EDIT: OUTER half of the tire was wearing faster!

 

If the inner half of your tires are wearing faster than the outer half then you have too much negative camber or your toe is off.

 

Yes, sir. I was either typing too fast for my brain, or just not paying attention.

The outer half of my tire was wearing faster so I added more negative camber.

 

We have a test and tune this coming Sunday. I'll take some tire temps and share with everyone. Just by looking at the tire wear, I gave it a little bit more negative camber. But we'll see how the temps come out.

 

I usually chalk the outer edge of the tire to see how much it's rolling over (however, the amount of tire roll over is also dependent on tire pressure). On my direzzas, I try to keep it so that the scrub mark is just at the top of the wear triangles, but no more than half way down the triangle. I've also had great success using a tire pyrometer. These are great because they can help you dial in tire pressure and alignment settings. For instance, at NJMP Thunder a month ago, my front tires were ~160, 170, 160 (outside to inside) in the front, so we lowered the tire pressure 2 psi and the temps on the next run were virtually perfect across the entire contact patch. The rears were something like 150, 155, 155 (outside to inside) which means I might be able to reduce the increase (closer to positive) camber a bit (running -1.5 in the rear, and -2.5 in the front).

 

Typical rule of thumb for an STU autox setup is in the range of 3-3.5 degrees negative in front, and 1.5-2 degrees negative in the rear. The car I drove at nats last year was at -3.3/-1.7. It's all very dependent on setup (spring rates, bars, etc), but anywhere near there and you're in the ballpark.

Edit: I just read your second post. How much spring are you running in front? 700lb sounds a little soft for the rear, though I'm sure there are some that would disagree with me (*ahem* Dallas)...

I've always used rear camber to try to stabilize the car, so I'd say you're on the right track.

 

Sorry for the lack of update boys. Clutch/trans said they had enough... so no tire temps.

As far as front spring rates. I want to say 560lbs?

Regarding the rear, the car seems unsettle through fast slaloms. I dialed in more rear camber and that kind of helped. Now the car pushes a little more on mid to corner exit. In the WDCR the lots here are not great. so any stiffer in the rear just makes the car unsettled.

 

You have rear toe out? You need rear slightly in. That will help settle the rear. Also ride height impacts rear stability. Generally lower is more stable in transitions.