Ever wondered what those numbers
were on the side of your tires, something like P235/75R17 or more commonly, P205/75R15, or as large as P315/45R17, so many combinations.
The numbers on the side of your tire, apart from various
others, is a sequence or coding which defines what the
size, shape, and height of your tire is. Here they are
Tire Type (P):
Tire Type refers to the tire that the vehicle is intended for. P for a passenger car, some others include: LT for a light truck, and T for a temporary or spare tire.
Tire Width (235):
Tire Width refers to the size of the tire from sidewall
to sidewall in millimeters (mm). Since the width of the tire can be affected by the rim size, the measurement is taken while it's on it's intended rim.
Aspect Ratio (75):
Aspect Ratio is the height of the tire in relation to
the width of the tire as express in percentage. For
example: if a tire was 205mm wide, and the aspect ratio was
75%: The height of the tire would be 153.75mm from the
bottom of the tire to the outside of the rim. High performance tires usually have lower aspect ratios (around 35 to 40%). This is because lower aspect ratios have better lateral stability for better cornering
ability. Many people buy wider tires with a small aspect
ratio with the intention of receiving better straight-line
traction, and realize that it's not what they expected.
Tire Construction (R):
Tire Construction is denoted by one of three letters on
the tire. The current method is radial construction for
radial tires and is denoted by an R. Older
methods were diagonal bias (D) or bias belted (B).
Rim Size (17):
Rim Size is the size of the rim that the tire is designed
to fit on, it won't fit properly on anything else. This
number is expressed in inches.
So there you have it, a P235/75R17 is a 235mm radial passenger tire with an aspect ratio of 75% designed for
a 17" rim. It's probably best sticking with a rim/tire
combination that results in a configuration that's no taller
but no shorter than your original combination. changing
to tires which are a lot taller/shorter will throw your speedometer off.