On tire pressures, the Yaris, and the Prius

[sbergman27]

Originally Posted by 1stToyota

I put zero stock in someone thinking that they've outsmarted Goodyear's and Toyota's engineers.

The 0.3% fuel economy per 1 psi rule of thumb applies to underinflation. One would expect to see diminishing returns as one increases the pressure above the placard values. Plus, I would expect to see a significantly shallower slope (less return per psi change) for the Prius' LRR tires than for regular tires.

Increasing and decreasing pressure is a trade-off, even between the placard pressure and the sidewall pressure. The tire probably won't fail under normal conditions. But impact resistance of the tire *is* reduced. Shock stresses on the wheel *are* increased. (Think "bending" in the case of steel, and "breaking" in the case of alloy.) Shock stresses on suspension components, such as the strut mounts, *is* increased.

It's not the normal driving that is likely to get you. It's that sheer 3 inch transition you hit in the construction zone, where the not yet repaved road meets the newly laid concrete, that you absolutely were not expecting.

I used to run my Sprint at 44 psi... and did sustain wheel and strut mount damage.

And, of course, stress on nerves and dental fillings is increased.

-Steve