If tire pressure is too high, then less of the tire touches the ground. As a consequence, your car will bounce around on the road. And when your tires are bouncing instead of firmly planted on the road, traction suffers and so do your stopping distances. You'll also feel a decrease in ride comfort and uneven wear.
Tires that are worn on the outside edges have been underinflated. There is excessive contact with the outer edges of the tire and the road surface as the vehicle travels down the road.
DO NOT read tire pressure off the tires side wall, that is not the proper pressure for your car. Open your driver's side door you can see a sticker on the racker panel, but it can also be found on the driver side door next to the door latch.
"Consumers need to inflate and maintain their tires properly so that they can achieve their intended levels of efficiency, safety, wear, and operating performance. NHTSA has previously addressed the importance of proper tire inflation to safety and fuel efficiency in various public service campaigns. NHTSA has also mandated that tire pressure monitoring systems (TPMSs) be installed on new motor vehicles. However, TPMSs are not a substitute for proper tire maintenance. Motorists must be reminded of the fact that even small losses in inflation pressure can reduce tire treadwear life, fuel efficiency, and operating performance." Read more...