Rear Tire Wear - Request Analysis on 1977

[kach22i]

The situation;

1. Owned car for four years, put 11,000 miles on it (96k-107k).

2. First thing I did was four tires on it, Yokohama ES-100. If I had to do it over the rear tires would not be as wide as they are, I tried to match what I found on the car, not match stock issue. Ed Mayo at PCA got back to me a week or two to late, wish I waited. Existing 32 lbs of pressure in both rear tires.

2. The car went into the shop the first month I owned it four years ago for a clutch, came out with lots of work done (engine drop) and several things having to be redone. Also shortly afterwords (the day I got it back for the third time) a mysterious whining sound which the shop refused to even acknowledge existed popped up.

3. The sound does not show up on cool days, have to toss it around a few turns to get it to flare up and is quiet faint, can't even hear it when the top is on and the windows are rolled up.

4. Pushing on the four corners of the car, the shocks might be the original ones from 30 years ago, but are not bad.

5. Torsion bars seem to be okay, both sides bounce back up at the same rate.

6. Emergency/parking brake does not engage or restrain the passenger side rear tire, the wheel spins freely with the parking lever pulled up.

7. With the car up on jacks I could not get any play in the rear tires when pushing on them in a front or back direction.

8. On the problem passenger rear tire; there is only a finger's width or 1/2" clearence inside face of tire to wheel well. I don't recall if that is when up on jacks or not. I can double check this. In either case there is no sign of rubbing or wear on the inside sidewall looking at tire and looking at wheel well.

9. The car does not sit level, the front sags down, and or the back is rising up. I've been meaning to adjust this, and this might be a major part of the current problem.

10. Video, pictures attached. Note the flash went off on insde of weel well pictures.

Video:
http://www.youtube.com/watch?v=D7cOM0op3xY

[kach22i]

More Picures.

[jabb]

Wearing out the center of the tire is usually form the tire being over inflated. The clearance you have between the fender and the outer outside of the tire does not sound like it is an issue. The car is sitting very high or maybe u just took it off the jack stands when u took the picture ?

[kach22i]

Originally posted by jabb
Wearing out the center of the tire is usually form the tire being over inflated. The clearance you have between the fender and the outer outside of the tire does not sound like it is an issue. The car is sitting very high or maybe u just took it off the jack stands when u took the picture ?

Tire pressure has been watched carefuly, still at 32lbs each side. You can see a line right in the middle of the tire about 1/4" wide - odd as heck. I can't see where it could be rubbing.

The car always has that nose down angle, it would be 1/2" lower in the front if I left the spare tire in. I pushed down all corners of the car before taking the picture.

The car has been getting weird and wobbly pushing it in a fast turn. The tire wear is one reason why I now see.

I've not been driving hard because I have to adjust the valves, I've not been driving it very much at all for that reason.

[kach22i]

double post..............

[mthomas58]

I'm no expert but I'm wondering if your corner balancing is significantly out of whack. If your front left and rear right tire are carrying the majority of the cars weight, it would seem to me that the rear tire would wear faster???

[rallyracer]

I'm not sure what your question is, but here's what I see.

1. I have no idea what your noise could be, but doesn't sound like the noise and tire wear would be related. Tire wear from bad shocks would be obvious and badly chopped.

2. The tire wear on the rear is actually pretty much even, so I don't see any alarming issue. both sides are well past useful life and within 1mm.

3. What appears to be a bit more wear on the passenger side could be:

-overinflation (you seem to disagree)
-spinning the tire on acceration a few times (most likely, but I don't know which tire spins so search for that)
-toe is off, but I would expect some very bad wear on one of the edges at your tread depth that I don't see in the pics.

I suggest getting new tires and checking alignment.
David

[madmmac]

Could be as simple as a bad tire casing. It does happen and I know we always try to overthink most things.

Either that or stop doing burnouts and start turning left more.

[kach22i]

Originally posted by rallyracer
2. The tire wear on the rear is actually pretty much even....

It's night and day the difference between the two rears.

The passenger side is worn badly in the middle and on the edges, just a little tread left 1/3 on the way in from each edge. It's very odd, I've never seen anything like it.

A bad tire casing?

I hope that's it. However, I really want there to be a connection between the noise and the wear. Perhaps that is keeping me from be objective. It just feels like there is a connection.

The car being out of level is also a connection, but I can't explain how or why. I really need someone who knows about these things to read this thread and speak up.

[kach22i]

A couple more pictures, the fronts look good.

This passenger rear is shot to heck.

[kach22i]

Good morning all, does anyone have any new theories?

I thought it was only the 993's which ate tires.

[Tim Hancock]

Kach, I just replaced my rear Avons with new as they were both wore badly in the centers (classic symptom of over inflation). My fronts still looked nearly new. One of my rears was wore slightly more than the other, but I do not remember which. I am now running lower rear pressure on my new year replacement Avons which should take care of my mid tread wear. I think I went down to 32 psi from 36.

I would get your alignment checked as well as a corner balance due to the fact that one of your rears is significantly more worn than the other. I think it is common for 911s to wear out the rears much faster than the fronts, so I wouldn't worry about that aspect.

[LARRY SHARP]

Actually sometimes underinflation causes that type of wear on Radials..

[Tim Hancock]

Originally posted by LARRY SHARP
Actually sometimes underinflation causes that type of wear on Radials..

Really? Tell me more.....I don't want to prematurely trash another set of rear tires.

[LARRY SHARP]

Low Profile tires sometimes have a softer sidewall and when the pressure is not up to spec it will allow the tire to Bow up in the middle at higher speeds. since the tire relies on the pressure to maintain the correct shape of the tire. But for 911's they will wear the rears out about twice as fast as the front tires from the rearward weight bias of the car.

[kach22i]

Thanks guys, I just used the SEARCH function "tire wear" and see that anywhere betwen 8,000 miles and 20,000 miles is normal for the rears (non-track).

I had no idea.

Link:
How many miles on a set of tires?

I'll look into corner balancing.

[nhromyak]

My dad's 80 has had the same issues once. He replaced his rear shocks and was happier than a clam (where does this saying come from or mean? time to google).

Your passenger rear, sure looks like center wear and outside cupping to me. What shocks do you have? Are there any oil or grease spots on the shock bodies?

Speaking to Bilstein, they said to do a push on the car after driving and see if the body bounces. I seriously doubt the 911s bounce from me pushing on the body at anyone corner, mainly due to the the friction of the torsion bar suspension.

Good luck.

[kach22i]

Originally posted by nhromyak
Are there any oil or grease spots on the shock bodies?

There is now, I sprayed PB Blaster on the heat exchanger bolts thinking that I'll be pulling them to do the valve adjustment.

I'll look for older heavier oil on the shocks, can't tell from the photos.

[kach22i]

UPDATE: 06/01/2007

I got a flat on the really bald tire a few days ago. Drove to the tire store just across the street from the job site while it was going flat and ordered some fresh rubber.

Tread, it's a good thing to have.


Same as before ES 100's

[aj88cab]

If your shocks are truely original (30 years old) then they are probably toast. Pushing on the bumpers isn't really going to tell you if they are good or bad on a 911. Replace all four with Bilstiens (HD or Sport based on street/track use) and you will be amazed at the difference. Of course, while your in there.........