Demystifying The Tire Sidewall Code
So, you need new tires for your car or truck, but how do you
know what to buy? What do all those alphanumeric codes printed
on the tire sidewalls mean, anyway?
If you're in the market for new tires, you may simply want to
replace your worn tires with exactly the same tire it came with.
But you MAY want to consider an upgrade. If you know how to read
the tire sidewalls, chock full of valuable information, you've
got an advantage over most people and are prepared to make an
informed decision. So let's get underway!
Tire Size Markings (example: P215/65R15 89H)
Broken down: P = Passenger Other designations are LT = Light
Truck T = Temporary (spare tire)
215 is the width (in millimeters) of the tire from sidewall to
sidewall. A wider tire has more grip but the bad news is that
you lose fuel economy, hear more noise and the tires don't work
as well in the rain.
65 is the aspect ratio The aspect ratio is the ratio of sidewall
height to tire width. With regards to aspect ratio, the larger
the number, the taller the tire sidewall. Tall (60-75) is great
for a quiet ride but causes howling in turns. Short (35-55) is
better for handling--more for sports cars.
R indicates Radial. This means it is constructed with a series
of support belts sideways under the tread. Other designations
include B for Belted Bias and D for Diagonal Bias The standard,
and what you'll see most often, is R.
15 is the wheel (or rim) diameter, in inches.
89 is the load index H is the speed rating Speed ratings
indicate the top speed under ideal conditions. Higher-rated
tires are usually made of softer rubber and will have shorter
UTQG tread life. Here are a few of the more common speed
ratings: R= 106, S=112, T=118, U=124, H=130, V=149, W=168,
Y=186. Along with this speed rating, you have a load index which
indicates the approximate weight the tire can carry. Some of the
more common load weights are as follows: 85 = 1,135 pounds, 86 =
1,168 pounds, 87 = 1,201 pounds, 88 = 1,235 pounds.
UTQG Ratings
Passenger car tires are accompanied by a UTQG Rating (Uniform
Tire Quality Grading, mandated by the Federal Government) which
rates the tread life of tires by looking at tread wear, traction
and temperature resistance. The UTQG Rating is usually found
opposite the tire size markings and will be in three separate
ratings: treadwear, traction and temperature.
The treadware grade standard is 100. A grade of 200 means the
tread would wear twice as well as a tire graded 100.
Traction grades run from AA to C, with AA being the highest
grade and C meaning the tire brakes poorly on both wet concrete
and wet asphalt.
Temperature grades rate the tire's resistance to and ability to
dispel heat. Those grades are A (resists heat well), B (not as
good as A) and C (passes minimum safety standards.) Keep in mind
that heavy loads, under-inflation of the tires, and high speeds
can all affect the tire temperature.
You should note that these tire grades rate tires measured under
controlled conditions. Factors such as driving habits, road
conditions, climate, etc., are not considerations and may affect
the actual performance of your tire.
DOT
DOT (Department of Transportation) indicates the tire is in
compliance with applicable DOT safety standards. Next to DOT is
an identification or serial number--codes that designate where
and when the tire was produced.
You'll also find other information on the sidewall such as the
type and composition of the tire, the maximum cold inflation
(PSI) and maximum load in pounds.
So as you can see, tires carry a huge amount of information. But
it's really not all that complicated once you learn to read the
code.