Over inflating a tire causes it to micro bounce. Beat up the suspension and lose contact with the road. You could probably go over by one or two PSI but when you start doing that crazy nonsense 45 psi junk that people think is right. You wind up with the car that is all over the road and for what? Suspension is taking a beating where the tires should be doing that for you
We keep our Prime XSE in Mexico ... not the best roads but not that different than Tucson either. Dropped pressures to 30 front and 29 rear just to try and smooth things up a bit, rather take the hit on the MPG's than replace bushings (our last three Prius all wore through the suspension bushings before anything else gave out) so will walk that fine line between too low of pressure and damaged 19" wheels vs too high of a pressure with damaged bushings. Would love to find some tires with larger side walls ... maybe swap out for 17" wheels and larger sidewalls - we will see.
Not sure if you just mean for the Prius or in general but in general over inflating does make a big difference in efficiency. It reduces rolling resistance. BUT, BUT it can be at the cost of grip or cornering control.
Mine starts complaining about low pressure at anything under 34. They end up around 37 because my pump's gauge is kinda garbage.
I raise the tire pressure above my nominal setting by 10% and then reset the TPMS. Then I lower the PSI back to my nominal settings. This makes the TPMS alarm sooner than it's typical 20% PSI loss. JeffD
