today's puzzle: how did all 4 tires get cupped on the inside?

Four months after I bought my Prius III last year, we discovered that the left rear wheel was so out of alignment that it ruined the tire in 5,000 miles, and then also ruined the one put in its place during regular tire rotation. Toyota replaced the entire set of tires, and I checked the alignment this fall and again this spring when I took off the snow tires. Everything looked fine. Nevertheless, when I rotated the tires today, the tech reported that ALL FOUR tires were substantially cupped on the inside, after only 6,000 miles on this set of tires. Road noise has become much higher.

It doesn't make sense that all four wheels got similarly out of alignment in just two months. Does anyone have a theory about what the problem is?

 

Yes, the dealer did the alignment, and presumably they should have been motivated to do it right so they wouldn't be responsible for ANOTHER set of tires.

After alignment, the camber/caster/toe stats were: LF 0.1/6.0/.13; RF -.6/5.3/.17; LR -1.3/.1; RR-1.5/-.02.

 

Tire pressure 42/40, no drivability problems such as pulling or vibration, . Since I don't see how all four wheels could get out of alignment in such a way to cup all four tires on the inside at the same time, the suggestion makes sense that the balancing at the tire shop was somehow wrong on all four tires.

 

The right rear was definitely out of alignment from the factory. Fixed that one, and the snows appear to be fine after the winter. Put on the almost-new summer tires in March, and they all cupped in two months. I am betting on poor wheel balance at changeover, although I'm not how it could happen.

I would also think that if all four wheels were so poorly aligned as to cause this problem, the gas mileage would go down because the tires would be scrapping (plowing) along the road. In fact my mpg has stayed up at 55-ish the past couple of months.