Does it matter which wheel/tire combo is on the car for a basic alignment?

On my '99 coupe, I have a set of '01 Z06 wheels/Kuhmo tires for summer/autocross/track day.

The car came with the Magnesium wheels which currently have Pilot Spot run flats which are obviously a different size and an inch narrower versus the Z06 wheels.

Reasons I think I need an alignment:

1) Never had one. 49,000 miles

2) The driver's side, inside tread way way hotter then the middle and outside tread after a session on the track.

Does it matter which wheel tire combo is on the car for the alignment?

 

 

IMHO, as long as the proportion of the two different sizes of wheel/tires is close, I would say that you'd be OK. Having said that, if the front end tech takes the car for a ride to see if it runs straight, etc, and makes compensations based on the one set of tires, you might get a different set of driving sensations when you change to the second set....Might create a problem.

 

thanks, and that confused the heck out of me

 

Let me try another way...Corvettes have different sized tires, front and rear. This difference has a proportion. Maintain that proprtion with ANY other wheels/tires, and you'll be OK. Go to a much larger tire in the rear for example, and two things happen. First, the computer will see this disparity in wheel speeds as outside of the acceptable parameters, and possibly kick in the traction control. Secondly, if the change to the rear, again, is significant enough, it will slightly "rake" the car, causing a caster change in the front alignment.

ALSO, each wheel/tire has a handling characteristic. You must have heard the term "radial pull" at some time. You put your "A" set of tires on the car, and take it in for alignment. Let's say this set has a slight pull to the right in it, and the alignment tech compensates so the car goes straight. You get home, and put the "B" set of tires on. This set of tires doesn't have any "pull" in it, so the car normally tracks straight, all by itself. However, the car was aligned with the "A" set, so NOW, with the "B" set on the car, the car drifts left.

See what I mean?

 

Hey Lead, yes. Thanks.

The Z06 wheels are about 1 inch wider versus my factory Magnesium set. The Kumho's mounted on the Z06 wheels are obviously different in size and wear versus the Michelen PS all-season run-flats. Different sizes, but, not radically different. There's no pulling to one side or another.

The Kumho's are my "summer" performance tires. I'm gusssing those should be the ones on the car when aligned.

I put the PS's on yesterday b/c I wanted to get a good look at the Kumho tread-wear in sunlight, and b/c I needed the run-flats for the next few days of lots of driving.

I made an amatuerish bird's eye view sketch of the Kumho tire wear and saw some interesting tread pattern wear in their short ~ 5,000 mile, 12 auto-crosses, 1 track-day, bit-around-town, lifetime.

On some (3 out of 4) tread sections, particularly the driver's rear, there's less wear, indicating a much smaller contact patch that one would otherwise want...I am accounting for the roughed-up wear on the outside edges from nasty auto-x surfaces. Some in-board tread shows very little wear.

Most scary, was the car felt unsettled, at Pococno, turning left, at speed on the bank.

If you think it matters, I'll try to scan and post the sketch.

Either way, I'm going to fax to an alignment shop, discuss, and put them back on for the actual alignment, unless the tech instructs otherwise.

thanks...

 

Somehow I missed this discussion for a couple of days. My suggestion, with respect to shops, anyway, would be to look up the Hunter Engineering website. I know that they used to list the shops that had their "roadforce" wheel balancers. See if they list any shops in your area with their "top of the line" alignment equipment.

For what it's worth, I would start with the Z-06 alignment specs, if it turns out that you car needs "tweaking".

 

Has anyone ever found what the exact rake specification range is?

 

The shop maual isn't very clear about determining this. However, there are 4 dimensions called out. Two of those dimensions are called the "Z height" and "D height", which are dimensions measured from "the lowest point of the ball joint, and the center of the front side of the lower control arm bolt". The "Z" is the front of the car and the "D" is the rear. "Service preferred" for the "Z" is 44mm (1.73"), and the "D" is 108mm (6.22").

There are also two other dimensions called out, "J" and "K" which appear to be some sort of "ride height" dimensions, but I don't see where the measurements are taken. These numbers are 6.0" and 6.22", respectively, front and rear. If I interpret these correctly, the "rake" spec is .20"

 

Jannetty Racing in Waterbury.

Ever heard of?

They have a Hunter machine. The owner wrote me back. Very cordial.

www.jannettyracing.com

here's the real basic sketch I made

 

"Blue", if I were to shoot from the hip, and hazard a guess, I'd say that your "thrust angle" is off, based on your tire wear diagram...

 

Lead, thanks for the help.
I need to plan a work
day-off for the alignment. Will let ya know. Much appreciated, brother!