3x Oversized Viva2 Tires Give Softer Ride
As an experiment, I just replaced the original Goodyear Integrity 185-65-15 on a 2008 Prius with Goodyear Viva2 205-70-15. The ride improvement is HUGE. I suspect the larger and more flexible sidewalls are absorbing bumps that the springs and shocks were not designed to absorb.
I think the 2008 Prius is over-powered, reducing the effective axle ratio by 8% may increase fuel economy. Time will tell.
I have installed custom tire sizes on many vehicles. Most tire shops refuse to install them. I have learned to take off the rims. If they ask what vehicle they are for, I say they are for a trailer. Walmart and PepBoys have never hassled me.