On a generation 3 the 60 might be a tad too tall or if you compress the suspension enough they may rub the 205 50s we have are no problem no matter how you're driving the car The 245 45s were really hard.
So 215/70R15 Yokohama Geolandars G015 are the biggest you can put on without lift, as long as you don't mind fender liner rubbing on the front. Bumps will rub. Lock to lock they have about half a inch to rubbing some metal frame piece on the front side of the wheel, like towards the bumper. But towards the rear, the tires have more space for turning, iirc. I think you can put on 235 tires, but you just have to find someone who actually makes that size, and what the rim and ratio sizes are as well. Not sure if the 15" prius rim supports that wide of tire now that I think about it. I think different tires have different widths rim requirements even if it's the same tire size. Tire rack has some data and google "Prius 15" rim specs" wheel-size.com. I can't quite remember, I looked up something like a 235/50R15 and it would "probably" work. I went from 38mpg to about 32mpg with my tire swap. Did a 370 mile roadtrip this weekend, 33mpg to and 36mpg from.
