What's in a Tire Code?
By Trey Dawson
Most people think that a tire is a tire. Many don't even bother to look at the data on the side of their
new rubber friend that gives them more information on what they're buying. Reading tire codes is easy once a buyer
gets to know the different symbols that manufacturers engrave on the sidewall sections. With a little knowledge,
the average person can become an expert in no time.
What is a Tire Code?
Tire codes give new tire buyers a great deal of information. The tire's manufacturer, type of material,
dimensions and maximum speed allowances are just some of the quick-reference data that tire codes offer interested
buyers. Codes are universal, and they offer the same information for every consumer.
Over the years, codes have become more complicated due to advancing technologies in tire fabrication. Tire codes
always use the standard metric system for measuring, which believe it or not, most Americans have unconsciously
gotten used to.
The first letter in any tire code determines the type of vehicle the tire supports. In the example, P215/65R15,
the "P" stands for passenger vehicle. Tire manufacturers would use an "LT" to show that the tire supports light
trucks, an "ST" for special trailers and a "T" for temporary or spare tires.
Width and Height
The next set of digits, 215/65 represents a tire's aspect ratio in millimeters. The 215 is the width of
the tire with 65 symbolizing its height, as of percentage of width. A 215/65 tire is 140mm high or 65% of 215 (215x
0.65). Construction Type and Diameter Some tires carry other data to help buyers quickly reference the type of tire
they're looking for. Letters after the rating and dimension data specify the tire's design with "R" standing for
radial, "B" for belted bias and "D" indicating diagonal bias. The number following a tire's construction type
indicates its radius. Thus, an "R15" tire is a radial tire with a diameter of 15 inches across.
Every new tire specifies the maximum weight it can support when inflated. Manufacturers write this
information directly on the tire. However, some manufacturers use a code to show its maximum load, using a number
taken from the European Tire and Rim Technical Organization (ETRTO). ETRTO load codes range from 60-125, which
indicate maximum loads from 250 kg (550 lb) to 1,650 kg (3,600 lb). A tire's maximum load information is especially
important for trailers or tucks that transport heavy cargo.
This rating is also marked on every tire and is sometimes combined with the load information. The speed
rating code informs drivers of the maximum speed that tire can support at maximum load. In the example, P215/65R15
87L, the 87 is the ETRTO load code, and the "L" is the tire's speed rating, taken from the ETRTO speed rating
table. These ratings range from "A1" (3mph/5kmh) to "Y" (186mph/300kmh). An "H" rating carries a maximum speed of
130mph or 210kmh at maximum load.
Road Conditions Markers
Winter storm and hot summer tires are very popular in the market today for those customers who live in places
with extreme weather. Sometimes tires may have special characters marked on them, telling buyers how they perform
under certain weather conditions. Road condition indicators can vary from simple drawings of snowflakes on the tire
to letter symbols, like M+S, which would stand for mud and snow.
Most tires sold in Europe, the U.S. and Canada have a Department of Transportation (DOT) number marked on its
side. This number gives a quick reference to the tire's manufacturer, plant number, lot, and date of production for
anyone interested. Knowing how to read tire codes can help buyers find the perfect match for their car. Being
prepared before entering a tire store improves communication and helps tire suppliers choose the best product to
make a consumer's vehicle the safest on the road.
When Trey is not online, he's usually getting his hands greasy in his auto repair shop. In addition to his
12 years of experience working as a mechanic, Trey enjoys learning about computer programming. He is the creator of
Size My Tires, an interactive tool for helping people find winter tires
for their vehicles.
Article Source: What's in a Tire