Let's test your diagnostic skills by judging tire wear!, My rears are torn up! Options

[blu94gt]

Ok so it's been a while since I've worked on cars for a living. My rears are showing two different types of wear patterns, in the form of cupping and inner tire feathering. The tires have always been noisy since I bought the car over a year ago, and I know the alignment isn't perfect. I post this up for a couple reasons: to get a second opinion before I dump some money into the car, and to educate some of the other guys on here about what all you can see just from how your tires are wearing.

Now in both pics you can see the dramatic inner tire wear in the form of light/dark sections, and you can somewhat see how there's a darker stripe across the tire where it is worn differently: this is where the tire is flat spotting/cupping, both my rears are pretty much 16 sided polygons lol.




Here's the educational part: the feathering on the insides of the tires is from the toe angles being negative, or toe out, meaning the wheels point outward when the car is moving forward. The cupping can be cause by a few different reasons: wheels/hubs out of line, unbalanced tires (usually REALLY unbalanced) or bad shocks/struts.

The cupping is what concerns me. I've never seen a cupping pattern this bad, the tire varies in tread depth from about 5mm to bald all the way around the tire. The struts aren't leaking and they pass the "bounce test", the wheels/hubs aren't bent or anything, and the wheels themselves are fairly well balanced. The only thing I can think of is the struts are bad, despite the usual factors.

Oh and if it matters the tires are Bridgestone Potenzas, don't remember the exact model number. They have been on the car a few years, have seen about 60k miles if I remember correctly from the PO's service records.

[blu94gt]

i think its a combination of over inflated tires + bad wheel bearing.

If its bad toe in or toe out would just cause the tires to wear out more quickly. I have not notice feathering or cupping due to toe in.

Camber in the other hand can cause the tires to feather.

hope that helps.

Well from what I've learned in school camber itself doesn't feather the tires, it's how camber affects the toe angle that causes the feathering.

The tires are kept at 32 psi, and last I checked the bearings are still good but I will put it in the air and check again this week.

how's the frame alignment and lug nuts torqued??

Frame is straight and lug nuts are all at 76 ft-lbs.

you ever think that the rubber bushings in the tension rods (not sure what toyota calls them) are worn out and you need new ones? they are the rods that are attached to the rear knuckles and go forward. i'll see if i can get a pick if you need it.

The trailing arms be what you're referring to?

I've considered before replacing all the bushings in the suspension, maybe with a switch to polyurethane bushings or something, but that's expensive and a pretty big undertaking (especially for a car that isn't on the track). Could help though, worn bushings can cause a lot of play in the suspension.