The Treadwear Grade
of a tire
is the numeric portion of the Uniform Tire Quality Grade Standards (UTQG)
that are printed on the sidewall of a tire. These standards were enacted by the National Highway Traffic Safety Administration (NHTSA)
, which is part of the United States Department of Transportation
. Higher treadwear numbers indicate that the tread
of a tire, and hence the tire itself, should last longer, although this is more true within a single product line
than when comparing the product lines of different manufacturers.
The wear on tires that are being tested ("candidate tires") is compared to the wear of Course Monitoring Tires (CMT), which are sold by the NHTSA at its UTQG test facility in San Angelo, Texas
. Both types of tires are mounted on vehicles that will be driven in a convoy
during the test, thus ensuring that the candidate tires and the CMT tires experience the same road conditions. The convoy, typically one of four or fewer vehicles, will drive 7200 miles on public roads
in West Texas
. Candidate tire wear will be checked during and after the test, and compared to the wear on the CMT tires from the same convoy.
The first CMTs were commercially-available Goodyear Custom Steelguards, and Goodyear Tire and Rubber Company produced all CMT tires from 1975 until 1984. From 1984 to 1991, the CMT tires were produced by Uniroyal. CMT tires are now "specially designed and built to American Society for Testing and Materials (ASTM) standard E1136 to have particularly narrow limits of variability." 1
Treadwear Grade Number
The treadwear grade
describes how long the tire manufacturer expects the tire to last. A Course Monitoring Tire (the standard tire that a test tire will be compared to) has a rating of "100". If a manufacturer
assigns a treadwear rating of 200 to a new tire, they are indicating that they expect the new tire to have a useful lifespan that is 200% of the life of a Course Monitoring Tire.
The DOT does not test tires. It depends on manufacturers to test their own tires and report the results. Unfortunately, this system has made treadwear ratings far less useful than the DOT had originally intended because tire manufacturers are able to use the treadwear grade as a marketing tool.
It is legal and permissible for a manufacturer to give their tire a 240 rating when their competitor's equivalent tire has a 220 rating; thus creating the false impression that the 240 tire is a better purchase because it will last longer. This tendency to inflate treadwear numbers has become so common that some manufacturers may report that ALL their tires have above average treadwear grades. Some are taking normal tires and reporting a treadwear of 600 or more, or giving a 220 rating to maximum performance tires with a reputation for poor tire life (e.g. the Goodyear Eagle F1 Supercar EMT).
Below 200= 15% of Tires
201 - 300= 25% of Tires
301 - 400= 32% of Tires
401 - 500= 20% of Tires
501 - 600= 6% of Tires
above 600= 2% of Tires
In general, manufacturers tend to overstate the treadwear of their tires in an effort to create the impression that their tires last a long time. The exception to this is in competition racing tires
, which customers expect to have very soft rubber compounds and very short lifespans. Manufacturers tend to give their race tires low treadwear numbers (often zero) to emphasize how soft and sticky their rubber is.
The ability of manufacturers to report their own numbers makes comparison of treadwear ratings between companies useless. Ratings may still be useful within a manufacturer's own line of tires. For example, a customer can reasonably assume that the higher treadwear rating on a Dunlop
SP 60 means it will last longer than the Dunlop SP Sport.