My 2017 Z06 has had 2 alignments to keep tire wear to a minimum. First alignment was around 1000 miles and second was this spring at 7700. First time corrections were significant and really improved the handling, second time was more of a checkup than anything else but a few minor adjustments were made to improve it.
I rotate tires every 3000 miles and measure and photograph them as necessary. At 9600 miles I recorded tire wear and even though it was 1900 miles since I had it aligned the tires and tread looked good. We just got back from a 3000 mile highway trip and as it was service time I pulled the wheels and saw inner tread wear on the rear tires that surprised me.
My question is, does anyone see anything in my alignment sheet that should have caused this condition.
Car now has 12700 miles and getting a new set of Michelins Super Sports.

 

Did you have luggage in the back of the car during your trip? Added weight will increase your camber thereby causing increased wear on the inner edge. 3000 miles at increased camber would cause that.

 

Do you have your first sheet? Curious where rear camber was set initially.

 

Does the entire circumference look like that? It almost looks like a locked wheel emergency skid mark rather than alignment. Any emergency stops made?

 

The only luggage amounted to maybe 40 lbs.
The whole circumference of the tire is worn like the picture, although this portion is the only one showing cord. And only inside edge of BOTH rears showing this wear.
No panic stops
Next....

 

The alignment sheet shows the first alignment (not Bowling Green)and then the current alignment.

 

It shows a before and after. Alignments are dynamic. So your before likely isnt going to match what the first alignment was set to.


With that said, your tire shows camber wear. -1.5 is more than I would be running on a street car which is where the have it set right now. I would be aiming for -1.2 or -1.3. Id also have the rear toed out instead of in (But that would make tire wear worse)

 

I would agree with atljar -1.2 is plenty for the street, but I wouldn't expect that kind of wear issue even at '1.5 it's pretty far out on the tire edge.
#1 low air pressure might have caused that, say 20 to 25lbs cold. I'd at least start at 30 to 32lbs cold on the street. 34 to 36lbs max hot.
#2 I would also double check the accuracy of the alignment. Both camber and toe. I had 2 alignments on my car and finally went to strings and a camber caster gauge and did it myself old school. Machines are great if they are kept in tune, sadly most are not. Your average street car doesn't require super accuracy, C7's with soft tires do.
#3 I assume nothing's rubbing on the tire. Definitely extreme but worth a check.

My procedure is top right. You wouldn't be removing washers, this is for a track alignment but order is the same for street. Caster 1st then camber and toe. Also if you lift the wheels off the rack or ground you need a good 15 to 20min drive to resettle the suspension to get an accurate reading. As you can see I have -2.0 in the rear and have never seen this type wear on my rear tires.

 

I think you are seeing the result of too much positive toe which is causing the inner tire surfaces to drag down the road. Most street driving recommendations for max tire wear specify a small amount of negative toe. DSC has recommended alignment specs that a lot of members are using for street and occasional track which have had members report good results. www.dscsport.com (look under technical for set up notes)

 

Lots of good comments (keep them coming). Tire pressure is set at 30-31 psi cold and checked regularly. Often check on the TPMS while driving if pressure are close and strange enough they are. Thought if the tires are scuffing down the road they would run warmer, hmmm.
Look forward to more suggestions.
Oh yeah, the shop in Seattle area that set this up has yet to reply to my concerns.
Appointment made at other shop to check and advise.

 

I experienced the same problem--Both rear tires. I also check my tires often for wear and proper pressure. The excessive wear pattern on the inside took place on a 1000 mile trip. What I don't understand is the amount of wear on the edge of the tire and yet the tread wear between the shoulders looks even. One would assume a larger camber change took place and a quick tire wear pattern occurred. I assumed the alignment was out. Since I don't track the car, I previously had the rear aligned with the min camber that the specs called for. I used a very good shop that I thoroughly trust. I bought two new rear Michelins and had the alignment rechecked. The alignment was good. I went back to the tire dealer and had them send the tires to Michelin for evaluation. Still waiting for an answer from Michelin.

 

Negative toe causes inner edge wear (toe out) . He's setup with overall positive. If anything it would be wearing outer edge (wheel face)


Also, low tire inflation would cause both inside and outside wear. Folks, this is a camber issue, or an alignment sheet that isn't correct

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If it was toe out I would agree with you but GM uses positive to indicate Toe In. Toe along with negative camber shouldn't cause that much wear on the inside edge. Tire wear is cumulative and just because you change the alignment doesn't mean the initial wear is going to even out. His before alignment settings indicate negative toe on the left side which is toe out. Overall toe was negative which also gave him a negative thrust angle. That meant the rear of the car was offset to the left from the front of the car some small amount when driving down the street. The front toe settings are sort of interesting since it looks like they were set to offset the rear thrust angle so the steering wheel would be straight while the car drives down the road sideways (dogwalks). The before right rear camber was also -1.8 degrees and I think the combo of total negative toe and high negative camber were the cause behind his inner rear tire wear.

Bill

 

Agree some..... and added weight in the rear also increases toe in on these cars. We have done extensive testing on C7s' and its amazing how much toe changes as the rear of the car moves up and down. FYI I run over 2.0 degrees negative camber on the street with excellent tire wear. The trick is keeping static toe as close to "0" as possible.

 

More weight on the front will increase front toe in as negative camber increases. More weight on the rear will increase toe out as negative camber increases. The tie rod is in front of the axle at the front of the car while in the rear the similar acting toe link is behind the axle. With the toe link behind the axle as the bottom of the tire moves outward in reference to the top of the tire the toe link holds the rear of the knuckle in place so the front of the knuckle has to turn outward to compensate thus making the wheel toe out.

Bill

 

i read something that GM offers a free alignment within x amount of miles on these cars?

 

Bill these are pics of our new Hunter alignment equipment we used during the test of the rear of our 2015 Z06. Notice under rear suspension collapse or acceleration the car toes in more than static. The toe out is with the rear up or under braking it surly toes out an extreme amount. One of the reasons these cars rotate so well in corners. Not sure why this doesn't follow your explanation.

static


Full down or under full acceleration


Full up or under heavy braking

 

I suspect what happens depends on what is happening with the upper and lower control arms and I suspect the relationship of those to the mounting points of the toe links in the rear and the tie rods in the front. From a static stand point if negative camber is gained by using the cams on the lower control arm to push the bottom of the tire outward the knuckle moves away from the toe link which would cause toe out. If negative camber is gained by pulling shims from behind the upper control arm to pull the top of the tire inward the knuckle would move toward the toe link which would cause toe in.

In your demonstration you are showing how toe is affected by suspension movement and I don't think that equates to how it is affected by initial camber settings. As the wheel goes up and down on the suspension I suspect it depends on how much travel is seen. If you go from full droop to full compression the relationship of the upper and lower control arms to each other changes to try and maintain the knuckle in as vertical position as possible. If they don't do that then they have the problem the first Corvairs had with their swing axle. Throw in the toe link's travel arc which is probably different than the arc of either of the control arms and you could get some interesting toe changes as the suspension goes through extreme movement. Within a limited range the arcs are close enough to each other to assume they are the same. These are my impressions but I can't do the math to verify that anymore as it has been 55 years since I took my undergraduate Statics and Dynamics course. Being an Electrical Engineer it was just one of those Mechanical Engineering courses I had to take. The old Chevy Power Books from the early 70s had a section on how to analyze all of those changes but I lost mine two moves ago.

Bill