rikhek

Getting a bit more wear on the inner most portion on the rear tires that the outside. Wear is consistent on both left and right. Current specs are:

Left: Camber -0.84, Toe -0.02.

Right: Camber -0.88, Toe -0.03.

Rear: Total Toe -0.06, Thrust Angle 0.01.

I realize there shouldn't be the differential I have on the camber but that's the "best" the tech said he could get. I DO have a new shop now and am needing advise on rear settings.

Rick

RAFTRACER

I believe the rear tire wear issue you speak of is caused by the toe out that you have in the rear of the car... no one that I know runs toe-out in the rear of the car. Toe out coupled with stock rear bushings is defineatly a performance no-no. The rear geometry and stock bushings are creating more toe out for you than your static settings. The rear negative camber is not too much, I would at least run 1/8 inch toe in total in the rear.

wallyman424

isn't negative toe the same as toe in?

according to his settings hes running -.06 total toe in.

he should be around -.25 total toe in for the rear. maybe its just the lack of toe in thats causing the wear patterns. or maybe he should just be doing less straight line driving and more high-g turning...

ghoffman

Eventually you will find out that you have to do this yourself to get it right.

0C5stein

Negative toe is toe out, positive toe is toe in. Anywhere from Zero rear to to in 3/16 is common. You need to go with what works well for you. 1/32 degree toe in is NOT enough to cause premature inner tire wear. Hell half of the alignment machines can't accurately measure less that 1/10 of a degree, and others are so accurate that they will drive you crazy trying to hold tolerances that the suspension will not even maintain. Case in point you can take a rear wheel on a live axle car (Ie. Cup car, camaro, mustang...) that is showing 0.00 toe on an accurate machine (I just bought John Beams Latest and greatest $30k wonder), grab the rear tire and twist it like you are trying to change the toe, measure it at 0.20 toe and come back 5 minutes later and it might be still reading 0.15 until you grab it and rack it back the other way. Don't get me wrong on my next statement because there are a bunch of self marketed alignment specialists tha couldn't find their Azz with both hands and a flashlight, but there are many of us, whom have polished our alignment skills and understanding of how suspension systems work, that realize that getting any alignment setting within 1/10 of a degree +/- .05 is more accuracy than will ever show up in the seat of your pants, in tire wear or on the stop watch. Don't kid yourself in thinking that you should concern yourself alignment readings of less than 0.1 +/- 0.05
What I'm saying is that for all intents and purposes, 0.02 is zero toe, and 0.03 is half of a tenth. It's mouse nuts!

Let me try a different approach because I don't think it is a toe issue:
If you are running stock tires then you probably have too much negative camber, because the outside tires will slide before they lean over enough (from body roll and latteral force) to get the tire perpendicular to the ground, hence wearing the inner edge.

Or, you just are not driving the car off of the corner hard enough for the available grip and negative camber that is in the rear end.

Here is another myth:
You can't figure out the correct camber to run on a track car based on tread wear. You need to use a pyrometer and measure tread segment work load. IMO That is the way to to set a suspension for the track.

TommyBoy72

Negative, RAFT knows what he is talking about.

-.25 would be a butt load of toe-out. More so than even a certain turbo dodge would need in stock autocross. +.25 is a lot of toe-in (1/2"). While it might allow an advantage for certain setups/driving styles, it definitely would cause the wear the driver is already complaining about.

rikhek

I'm running 18/10.5 OEM Z06 wheels on all 4 corners with 275/305 Toyo RA1's front/rear.

Car is being driven plenty hard off the corner. All grip is being utilized.

I appreciate the response and don't really know how it ever got it "set" at negative (i.e., toe out) in the rear. I know better and I guess was brain dead when I looked at the sheet....It just didn't register. Worse yet I just went and looked at my alignment sheet and the front toe is "backwards" as well. Has +0.01 on each side on the front. It's slightly toed in. Not right...

Appreciate your help

Rick

0C5stein

Okay, I wasn't saying that to be critical, I was just saying that maybe the tire wasn't being deflected by laterial gs enough for the negative camber setting. So if that isn't it...
do you drive the car alot on the street?
That much negative camber could cause the inner edges to wear prematurely.

Are you running to soft of a rear spring? That would allow the rear end to compress under hard acceleration which adds considerable negative camber. Do you drag race with those tires too?

Do you have any tire temps Immediately after a lapping session?

rikhek

I didn't take it as critical, I appreciate your time and effort responding and value the input. Just responded as I'm generally in the top 10% in the fast/advanced group measured by lap times. I must not be above average intelligence as I didn't pick up on the fact that my alignment was "backwards". Need tp pay closer attention to what my alignment "professional" does. I feel stupid.

Car is driven as a weekend car on the street and 10 - 12 open track days a year. All at Hallett in Oklahoma.

The R compound tires are NOT driven on the street except back and forth to the track. Less than 100 miles round trip. I have 2 sets of wheels/tires.

It's a coupe with Z06 springs, sways and shocks.

No drag racing.

I've taken temps in the past and they were consistent.

Also should mention the inside wear on the rears is not terribly bad at this point. I only have 2 track days on this set of rear scrubs and noticed a slight difference in my normal wear. These last 2 track days were both on the "bad" alignment.

Another point is I've not had it aligned since putting on the Z06 springs and adjusting the ride height and rake. I put the springs on right before my last track day so I imagine this is also a contributing factor. I know I need it aligned due to the spring/height change but couldn't get to the shop prior to the track day. I'll be going tomorrow....

Rick

rikhek

One more question. When I have the car aligned it's on my 17/18 street wheels. They are stock OEM Z06 wheels.

My track wheels are 18/10.5 OEM Z06 wheels on all 4 corners. Do the 18" fronts I use on the track have an effect on the alignment?

Rick

wallyman424

i was just asking. i've always referred to it as negative. i take the measurement in the front of the wheel minus the rear of the wheel, and that yields a negative number for toe in.

and for .25 toe in, i meant total toe, so .125 on each side.

0C5stein

Your front street 17 x 9.5 have 54mm offset and your 18 x 10.5 track fronts have 58mm offset. This is only about 1/8" difference and will virtually not effect on your alignment.

On another point, if you changed springs and most specifically your ride height, then it will have an effect on Caster, Camber and toe, so I would say that an alignment is in order.