Ok,

I just got back from getting a set of Michelin Pilot 285/30ZR19 and 335/25ZR20 for my 2010 ZR1 - this is my first tire change at about 13,000 miles and I had some wear on the inside right front, otherwise they would have gone another 2k-3k miles.

I found the Pfadt alignment sheet here

http://pfadtracing.com/pdfs/Corvette...09.12.2011.pdf and went with the performance street (aka the mildest) tune.

As I understand it, the Pfadt sheet uses a weird way of defining toe in that could be confusing, so I wrote the following down myself based on the Performance Street setup on Pfadt's sheet...

Front Camber: -0.7 to -0.9
Front Caster: 7.5° to 8.5°
Front Toe: 1/16" TOE IN

Rear Camber: -0.4 to -0.6
Rear Toe: 1/16" TOE IN

I got the following back...



I think they just used 2009 Z06 as a sheet to fill in the blanks, because the alignment guy even called me during the align to confirm that I wanted toe in - he said his boss told him that I wanted something strange like toe out and he didn't think his boss had understood me correctly so he clarified.

I DO NOT know much about alignment terminology so I didn't realize he was talking in degrees with me on the toe in and I thought he was basically confirming with me that I wanted toe in, not toe out.

Can you guys tell me what I actually ended up with and is it good, bad or ugly? I apologize but suspension is NOT my expertise at all... TIA!

If you can't read that - here is the original scan...

http://farm6.staticflickr.com/5539/9...71ebbba4_o.jpg


EDIT: I live fairly close to the shop and it was 6pm Friday night so there was no way for me to responsibly put any stress on the handling of the car, so I couldn't tell anything much about the new handling, it did track very straight when I took my hand off the wheel on the interstate. ALSO, he did tell me that he was altering my specs to account for the crown of the road... which makes sense to me. So that is why the right and left are slightly different.

EDIT 2: I'm trying to read this carefully and starting to feel pretty good about it. First, I had to ignore the 2009 Z06 specs. The specs I ASKED FOR are what he correctly seemed to be trying to achieve, with the exception of trying to counter for crown in the road which the Pfadt settings don't seem to care about. Second, I have to hope that green 0.6° to green 0.8° are about 1/16" toe IN, if so then he is really spot on there. Third, it appears the left rear was - for some reason? - WAY off to the point of even upsetting the thrust angle. Interestingly, the only abnormal tire wear was the INSIDE RIGHT FRONT which was cords while the rest of the tires appeared to wear FAIRLY evenly. Maybe that makes sense if the LEFT REAR was thrusting the car in a way that wore the RIGHT FRONT, but I was expecting (wrongly?) to find too much camber on the right front.

 

One more question, this is bugging me - for some reason they did the alignment BEFORE putting on the new tires. Everything in my logical mind screams that this would result in a bad alignment on the new tires. But maybe not and maybe it has nothing to do with the tires themselves? Anyone have any actual knowledgeable input?

 

Your good with these settings inside edge wear should stop
as for setup with old vs new tires the sidewall flex enough that it is no problem. (translation your aligning the chassis not the tires)
you should be very satisfied with this

 

The car will sit differently with new tires. The alignment was a waste of $ doing it on the old tires.
The alignment you got was not what you asked for.Your numbers and the machine numbers need to match. Some R not even close.
Get your $ back and run...................
Robin

 

Ps;
I put my weight in salt bags in the drivers seat when its done.

Robin

 

If the before readings are correct the car should drive a lot better. It was set up with both front and rear toe out. I attached a pdf file that shows how to convert toe readings from degrees to inches. Just choose the diameter the measurement was taken on. For instance, if you were using the string method to set toe and had a difference of 1/32 more distance from the string between the front edge of a 19 inch rim and the back edge of the same the degrees at that wheel would be ~.095 degrees of toe in.

Bill

 

I am no expert but you still have to much toe for street Pfdat specs.

I run .01/.02 front toe. With .06 camber. And 7.8 caster.

Toe is what scrubs the tire causing wear.

The tech did not take his time. My job took 90 minutes to get even.

It is a back and forth job due to every adjustment changes the prior.

 

That got interesting fast...

Well, the fronts are 25.8 inches in diameter and the rears are 26.6 inches in diameter according to tire rack.

If I am reading that graph right, then I would be at more than 1/32nd toe in but less than 1/16th toe, correct? EDIT - NEVER MIND, I need to add those together. So my toe is a little over 1/16th.

Robin, this is a street car so I don't need weights in the driver seat. I do want a good alignment for performance street driving, but I want to avoid tracking ruts and I'd like decent tire wear. I am curious about the alignment on old vs new tires. This is a pretty established Goodyear tire store, I would think they wouldn't align it that way if it were really a disaster - but again, I just don't know.

It seems like he did get pretty close to the specs I asked for though - allowing for his cross adjustments for road crown, I think he hit most of my numbers square - no?

I asked for Front Camber: -0.7 to -0.9 and got -1 on the left (which is 0.8 adjusted for the crown in the road) and -0.8 on the right.

I asked for Front Caster: 7.5 to 8.5 and got 8.6 on the left (which I assume is adjusted for crown vs the right) and 8.2 on the right.

I asked for 1/16th toe in and I'm not dead sure how to read that yet, but I appear to have been toed out before and I am toed in now.

On the rear I asked for Camber of: -0.4 to -0.6

I got -0.5 on the left rear which is dead on and -0.3 on the right rear, I don't know if that is a crown adjustment, or if he wasn't able to get it farther than that or what? That seems to be the only one that is off...

Rear toe was terribly toed out before and he has it identical on both sides and hopefully close to 1/16 toed in now.

I'm open to any thoughts, I don't know much about this and I'm trying to learn. But I'm not setting up a race car, just a spiritedly driven street car.

 

This is an interesting page:

http://robrobinette.com/ConvertToeInchesToDegrees.htm

If I put 1/16 (aka 0.0625) and a tire diam of 25.8 I get a measurement of 0.07° which is exactly what the tech dialed in. Thoughts?

 

If I'm reading the chart right the diameter measurement is to be taken on the wheel (19" & 20"), not the tire.

 

I recently had my '13 427 checked at 750 miles, as I noticed a little tramlining on one road where my C5 would handle it unnoticed. Car is FE3 suspension and the same size tires as the OP. Bill Dearborn suggested that the C6 should handle it the same, so it went to the alignment shop.

I copied the FSM page with alignment specs for this specific model and took them with me. The shop brought the car up on their alignment computer, and the FE3 specs on their machine did not match the FSM, however the 2012 FE4 (Z06) specs on their alignment computer were an exact match - makes sense and that's what they went with. Lesson learned on all future alignments - take the specs with you and be sure the tech uses the correct spec.

All looked good, except like the OP, left rear was toed way out. Tech corrected that, brought the other wheels to the exact spec, and the problem went away.

 

3786 miles- 2013 GS. Front alignment was spot on to Pfadt specs--however the right rear was way off! The tech set it up to the Pfadt specs I brought him. Car drives MUCH better.

Why is the factory dropping the ball on the alignment (Front & Rear) ?

When we test drove the car I complained about how it felt (Following the grooves, twitchy response). Dealer checked the tire pressures and said to bring it back if I wasn't happy. I had the alignment done at a local tire shop that I trust.

 

The tech at the shop I go to says he seldom sees a newer Vette in his shop that was all in spec on the alignment -mabe a little self-serving, but I have no evidence to the contrary. He mentioned he believes some of them have to do with the way they are tied down for transport, either truck or rail.

 

No rail shipment in the US (yet).

 

We've had three new Corvettes (2001, 2006, 2009) and every one of them was outside even the generous GM specs after a few thousand miles. You can get a warranty alignment on a new car within a certain mileage range, and should do so.

I'm not sure if the factory isn't aligning them correctly when built, or the fact that the car settles somewhat after a few thousand miles is throwing things off. Either way, I'd get it checked.

 

Please explain what parameter(s) will change with the new tires (camber, caster, or toe); and why they will change.

 

......and they likely will not be in the future. I seem to recall on one of the factory tours they said that they found that the cars were getting too much paint damage during rail shipments,which is why they are now shipped by truck.

At that time, when Bowling Green was producing XLRs they were shipped in enclosed trucks. Vettes in open trucks.

 

I'd like to know also

 

When measuring in inches the farther out from the centerline the greater the distance. Degree measurements won't change. Form a V with your fingers. The distance between your first knuckle is less than between the finger tips even though the degree is the same.


If the old tires are worn to the inside they do not sit the same as new tires. They are worn with built-in camber on the face of the tread. The inside edge could have 7-11/32" less tread than new. I imagine it is worse with stiff sidewalls vs. old bias tires.

But, I could be wrong.

--Dan

 

IIRC, an alignment is done on modern equipment with the jigs attached to the wheels, not the tires. So I don't think tire wear would make any real difference.

But my wife told me I was wrong, once.