Deciphering My Alignment

Yes, you will need to shim the LR to correct the toe. My car also had this issue, although the toe was .40 on the RR (max spec is .28 IIRC). I noticed weird handling at freeway speed as a result. I went about 8k before getting it fixed and did not see any strange wear pattern, but the OEM Goodyear tires had a tendency to wear on the outside edges no matter what the inflation pressure was set at.

 

Yes, to shim the rear wheel, the shim would be placed between the backing plate and the rear axle flange. There are 4 bolts that hold the hub and backing plate to the rear axle. The 4 bolts are loosened and the shim is inserted to move the backing plate and hub in the direction to correct the toe.

A tire shop that also performs alignment or an alignment shop would be able to do this for you and then check to make sure that the toe has been corrected.

The dealer will probably not do this for you because it is not the accepted repair per the Toyota service manual. The service manual says that if the rear alignment is not within spec, then the axle beam must be replaced. $$$$.

 

Unless you have a ton of miles (you didn't say), I think the wandering is related to the alignment because my car was much improved after the rear toe in was brought into spec.

 

This is normal for a Gen 2 Prius and is because it has no toe-in. The previous owner may well have asked for some toe-in to be added to prevent the wander.

The toe-in is specified as zero because toe-in wastes some energy. Fuel economy will be slightly lower, but I'd sacrifice some economy to have a more stable car.

The Gen 3 Prius has a little bit of toe-in, about .25° as I recall.

The lack of toe also causes the tyres not to heat up, which means - if they're standard summer tyres for the size - they often don't grip as well. Grip is a complex chemical reaction between the tyre surface and the road surface, and the tyre compound is designed to work at a certain temperature range.

The OE tyre in the UK, Bridgestone's Turanza ER30, is also OE for BMW and Mercedes cars which run much higher levels of toe-in, and hence run a lot hotter. (We use the same size as the US Touring model, 195/55 R16.) I found that the tyre just tends to slide across the road and wear out quickly - down to 3mm tread after only 21,000 miles. I've replaced them with Nokian 'H' tyres that I'm hoping will grip better at cooler temperatures, being designed for a Finnish spring and autumn. Too early to tell but signs are good so far.

Some US owners have reported good results with the Nokian i3, which is available in the 185/65 R15 size used by the base model Gen 2 Prius. It has a lower speed rating than the H but you really don't need a 130mph rating.

 

I think that you should first try to get the left rear wheel toe shimmed so that it is within spec. You may then find that the car's handling is acceptable.

 

In case you don't want to set up the alignment yourself, you can also go to a local speed shop/garage that specializes in car modification and race prep, and get a 4-wheel alignment. For me it's $180 locally.