First, take a look at the treads on the tire. In all car tires are vertical metal
bands that are under the rubber. Examine each tire to see if you see any signs that
this metal is beginning to come through. If you can see a substantial amount of this
metal, it is very important to change your tires. If there is no sign of the metal
at all, you probably do not have to change them yet.
Next, take a penny and stick it in the crack of the tread, upside down, so that Abe
Lincoln's head is facing you and the ground. Look carefully to see how much of his
head you are able to see. Ideally, almost all of his head will be hidden behind the
tread. If you can see some of the top of his head, it is probably time to buy new
tires. If you can see all of his head, you should buy tires soon.
Look for the patterns of wear on your tires. If the tires have been under inflated
for a long period of time, often you will see a lot of wear on the outside edges
of the tires. If they have been over inflated for awhile, the middle will be the
most worn. It is important to drive with properly inflated tires, both for safety
and gas economy. If the wear is deep, and the penny test and metal bar test fail,
get your tires replaced soon.