Underinflation results in unnecessary tire stress, irregular wear, loss of control and accidents. A tire can lose up to half of it's air pressure and not appear to be flat. Overinflation can also result in premature tire wear.
A bad jolt from hitting a curb or pothole can throw your front end out of alignment and damage your tires. Normal wear-and-tear over time will also effect your alignment. Have your alignment checked periodically (yearly) to ensure that your car is properly aligned.
Promotes uniform tire wear. Regularly rotating your vehicle's tires will help you achieve more uniform wear. Unless your vehicle owner's manual has a specific recommendation, the guideline for tire rotation is approximately every 5,000 miles (7,500 miles maximum).
Measure it -- and inspect it.
Advanced & unusual wear can reduce the ability of tread to grip the road in adverse conditions. Visually check your tires for uneven wear, looking for high & low areas or unusually smooth areas. Also check for signs of damage.
Where to mount two new tires
NEW TIRES ON THE REAR
Understeer is the condition where the front tires lose traction before the rear tires, and where the sensation is that the front of the vehicle is "pushing" or "plowing" through a corner. With extreme understeer, the car will leave the road front wheels first.
This condition is considered the safest for the average driver and most OE vehicles have understeer purposely built into their handling characteristics.
The correction for understeer is to reduce speed and steer angle until the front tires regain traction.The Wrong Way
NEW TIRES ON THE FRONT
Oversteer is the condition where the rear tires lose traction before the front tires, giving the sensation that the rear of the vehicle is drifting or sliding. With extreme oversteer, the back end will try to pass the front end, resulting in leaving the road rear wheels first.
This condition is considered favorable by expert performance drivers, but requires more work to control.
The most simple correction for oversteer is to turn the front wheels in the direction of the skid (same correction as for rear end sliding on snow and ice). But there are different causes for oversteer, and different corresponding solutions.