Inner rear tire wear. Camber?

By design, the rear wheels splay outward at the bottom (camber). This keeps the car more stable during cornering, but the trade-off is the tires wear a bit faster towards the inside. You're correct that there's no readily doable camber adjustment, short of taking the entire wheel bearing assembly off and installing aftermarket shim.

If it's just one or two 32'ths difference in tread depth, outer to inner edge of tread, I would just live with it.

 

Toe-in or Toe-out causes wear. Unless it is extreme camber, it doesn't cause wear.
Since it is only the one tire, I would check for damage.
Are the other three okay, or do they show wear also?

 

You can add shims

 

I put a carpenter's square on our garage slab and slid it up against the right and left side rear wheels, noticed quite a difference in the camber. Evidence of some manufacturing "drift" in the solid rear axle I think. As a consequence I've got similar, but maybe more minor, increased wear on the inside. It's not a lot of difference, so I just let it be.

Maybe try the the square check, post what you find.

 

Since it is only the one tire, I would check for damage.

 

If you are getting INNER wear on the tire, you have a problem with toe out with that wheel.
Or EXCESSIVE camber. You can stand behind the car at about 20 feet and you will see the top of the
wheel leaning inward. Something is bent.

Are you sure they didn't just rotate the tire from the front to the back? It is extremely rare for rear tires
to wear like that unless there is some sort of damage. Since there is not toe settings on the rear of the Prius.

 

There is an amount of rear camber, by design. Again, I've notice a fair amount of difference, left vs right, on ours, so manufacture tolerance of the rear solid axle are maybe not tight enough. If you run a rear tire hard into a curb it would tend to reduce camber? Or introduce some splayed out toe, lol.

Not 100% sure the rear camber spec is in the attachments, will check later.

 

You could add washers to the bolts that how the wheel bearing on and change the angle. But I believe
you would be putting stress on the wheel and bearing in a way it is not designed to have.
Plus, the car would pull to one side. Which could get some adjustment with an alignment.
But I can't imagine someone doing the alignment and NOT seeing on the display of the alignment screen
that the wheel was way off setting.
If that wheel has been on the back for a while and didn't suffer the damage from being on the front,
you either have a defective tire, or some damage to the where the bearing is, or bearing.
Since even a fixed axel like on the Prius moves up and down camber will change as you go over bumps.
1 or 2 degrees will not cause wear on one edge.

 

I think rear camber spec is on page 11 (of 13) on the doc with suffix "Wheel Alignment".

 

This is what I get, checking with carpenters square. My tires have a rim protector crest, so I used that for a sharp edge:



Spec is 1.47 degrees (17" wheels) plus/minus 0.5 degrees, and no more than 0.5 degrees variation, left vs right. In my case, left side is barely within spec, right side is well beyond, and the variation between the two is about double the allowable.

Still seems ok though.

I used AutoCad, but without, you could use the trig functions on a calculator, I believe tan? As an example, for the left side:

0.375/19.625=tan of the angle

 

Your right side is off. Still very MINOR. Could be a worn spring. Maybe your battery gained weight and is causing it to sag.
Considering how you measured it, it's close enough. Only an alignment machine will be able to give you the true reading.

 

Yeah, that's what I'm thinking. Measurements aside, the wear variation across the tread face is minor, and the handling seems ok.

 

You shouldn't "guess". Take it to a shop you trust and have them check it out. It wouldn't be easy to bend it.
So there should evidence of it. You can jack it up and grab the wheel at 9 and 3 o'clock and give push hard with
one hand and pull with the other and see if it moves or jerks. Shame thing at 12 and 6.
2 years ago I have 2 new tires, on the rear of my Van had severe outer tire wear at 3000 miles.
I'm glad I noticed it. They replaced them for free under warranty.
And like I said before, stand back 20 feet or so and look at the wheels. Do they look straight?
Does the left one seem the same as the right one? Or does it look like the rear of it is pointed inward?