Can stopping distance or handling be hurt by running high tire pressures like 40-44psi vs the standard 32-35psi? I found a chart/test on the web at the very bottom of this page which shows better stopping distances at 35psi vs lower, but it doesn't test higher than 35psi. I was wondering if it is safe to openly recommend to friends and family to run 5-7psi higher than the vehicle placard shows to improve fuel economy, but I wouldn't want someone to get into an accident and blame reduced stopping abilities on high tire pressures.
Increased tire pressure works because it puts less tire surface area on the road, so less gripping to overcome by the car. This reduces traction, which increases stopping distance. Benefit is you get better mileage. I think as long as you explain this to everyone it is fine. The two are related to eachother.
I believe that the use of 44/42 psi tire pressure on Prius improves handling, traction and the tires' ability to stop the car. Improved MPG is a side-benefit which results from lower rolling resistance. The reason that I believe that is because when Prius owners use 35/33 psi, they will typically notice increased tire shoulder wear. This is an indication that the inside of the tire tread has less contact with the pavement. When 44/42 psi is used, typically more even tire wear results. If tire wear is more even, then it would stand to reason that tire surface area on the road is increased, and traction should therefore be improved. MPG is improved because there's less rolling resistance with more inflation. If you go to extremes and overinflate the tires to the extent that your center tread is now wearing out faster than the shoulders, then I would agree that tire surface area is reduced and hence traction would be reduced.
Increased tire pressure works because it reduces the amount the sidewalls flex. Flexing of the sidewall uses the kinetic energy of the vehicle to create heat. This heat results in lost kinetic energy that must be replaced by burning more gasoline to maintain speed. There probably is an upper limit to increased tire pressure where rolling friction/traction is reduced by decreased contact area with the road. Unfortunately, I'm not sure what that limit is. Keep in mind that as the contact area shrinks, the pressure of the rubber on the road increases (less square inches, same vehicle mass equals more pounds per square inch of contact).
I'm with Patrick as well. Race care drivers don't run soft tires! The best performance is with max cold setting in all conditions. Hal
I wonder if we should start a thread collecting data for tire model, psi, longevity, and uneven wear. At 44 psi, my 42000-mile 45-month integrities have enough tread to last for the next 10 month.
