NHTSA rates the quality of tires based on three criteria: temperature, traction and treadwear.
TEMPERATURE
Letter grades are used to rank tires for heat resistance, graded "A" (highest); "B," or "C" (lowest).
A "C" grade represents the minimum performance standard required by Federal regulation.
Currently, 27 percent of tires are rated "A;" 59 percent are rated "B;" and 14 percent are rated "C."
A tire's ability to resist heat is an important safety factor. Tires driven long distances in hot weather can deteriorate, leading to rare instances of tread separation and blowouts.
TRACTION
Also rated with letter grades. A tire that carries a higher grade should allow a car to stop on a wet road in a shorter distance than a tire with a lower grade.
Traction is graded "AA" (highest); "A;" "B," or "C" (lowest). A "C" grade can indicate poor performance. Currently, 3 percent of tires are rated "AA;" 75 percent are "A;" and 22 percent are "B." There is only one "C" rated line of tires.
TREADWEAR
A control tire is assigned a grade of 100. A tire with a grade of 200 can be expected to last twice as long as the control tire, while a tire with a grade of 80 is normally less durable.
Currently, the highest reported treadwear rating is 700; 98 percent of tires rank 600 or below; 92 percent rank 500 or below; 72 percent rank 400 or below; 40 percent rank 300 or below; and 5 percent rank 200 or below.
Tread Wear: This number comes from testing the tire in controlled conditions on a government test track. The higher the number, the longer you can expect the tread to last.
Since no one will drive his or her car on exactly the same surfaces and at the same speeds as the government test track, the number is not an accurate indicator of how long your tread will actually last. It's a good relative measure, however: You can expect a tire with a larger number to last longer than one with a smaller number.
Traction: Tire traction is rated AA, A, B or C, with AA at the top of the scale. This rating is based on the tire's ability to stop a car on wet concrete and asphalt.
It does not indicate the tire's cornering ability. According to this NHTSA page, the Firestone Wilderness AT and Radial ATX II tires that have been in the news have a traction rating of B.
Temperature: The tire temperature ratings are A, B or C. The rating is a measure of how well the tire dissipates heat and how well it handles the buildup of heat. The temperature grade applies to a properly inflated tire that is not overloaded.
Underinflation, overloading or excessive speed can lead to more heat buildup.Excessive heat buildup can cause tires to wear out faster, or could even lead to tire failure. According to this NHTSA page, the Firestone Wilderness AT and Radial ATX II tires have a temperature rating of C.
Originally posted by The Internet: DETERMINING TIRE DATE CODES
How old are the tires on your vehicle? The date of manufacture is indicated by the last group of digits in the DOT manufacture code on the sidewall of the tire. The number is often stamped in a recessed rectangle. The DOT code tells who manufactured the tire, where it was made and when. The last group of digits in the code is the date code that tells when the tire was made.
Before 2000, the date code had three digits. Since 2000, it has had four. The first two digits are the week of the year (01 = the first week of January). The third digit (for tires made before 2000) is the year (1 = 1991). For most tires made after 2000, the third and fourth digits are the year (04 = 2004).
In the photo above, the date code is 8PY806. The 8PY is a manufacturing shift code, and the date the tire was actually made was 0806, which is the 8th week (08)in the year 2006 (06).
The date of manufacture is essential information for car owners and tire buyers because tires deteriorate even if they are not used. European automobile manufacturers recommend replacing ANY tire that is more than six (6) years old, including the spare tire. No such recommendations have yet been made by domestic vehicle manufacturers.
When it comes to determining the age of a tire, it is easy to identify when a tire was manufactured by reading its Tire Identification Number (often referred to as the tire’s serial number). Unlike vehicle identification numbers (VINs) and the serial numbers used on many other consumer goods (which identify one specific item), Tire Identification Numbers are really batch codes that identify the week and year the tire was produced.
The U.S. Department of Transportation (DOT) National Highway Traffic Safety Administration (NHTSA) requires that Tire Identification Numbers be a combination of the letters DOT, followed by ten, eleven or twelve letters and/or numbers that identify the manufacturing location, tire size and manufacturer's code, along with the week and year the tire was manufactured.
Tires Manufactured Since 2000
Since 2000, the week and year the tire was produced has been provided by the last four digits of the Tire Identification Number with the 2 digits being used to identify the week immediately preceding the 2 digits used to identify the year.
Example of a tire manufactured since 2000 with the current Tire Identification Number format: In the example above: DOT U2LL LMLR 5107 DOT U2LL LMLR 5107 Manufactured during the 51st week of the year DOT U2LL LMLR 5107 Manufactured during 2007
While the entire Tire Identification Number is required to be branded onto one sidewall of every tire, current regulations also require that DOT and the first digits of the Tire Identification Number must also be branded onto the opposite sidewall. Therefore, it is possible to see a Tire Identification Number that appears incomplete and requires looking at the tire’s other sidewall to find the entire Tire Identification Number
The use of a partial Tire Identification Number on the one sidewall (shown above) reduces the risk of injury to the mold technician that would have to install the weekly date code on the top sidewall portion of a hot tire mold.
Tires Manufactured Before 2000
The Tire Identification Number for tires produced prior to 2000 was based on the assumption that tires would not be in service for ten years. While they were required to provided the same information as today’s tires, the week and year the tire was produced was contained in the last three digits. The 2 digits used to identify the week a tire was manufactured immediately preceded a single digit used to identify the year.
Example of a tire manufactured before 2000 with the earlier Tire Identification Number format: In the example above: DOT EJ8J DFM 408 DOT EJ8J DFM 408 Manufactured during the 40th week of the year DOT EJ8J DFM 408 Manufactured during the 8th year of the decade
While the previous Tire Identification Number format identified that a tire was built in the 8th year of a decade, there was no universal identifier that confirmed which decade (tires produced in the 1990s may have a small triangle following the Tire Identification Number to identify the decade).
And finally, hold on to your sales receipt. Most tire manufacturer's warranties cover their tires for four years from the date of purchase or five years from the week the tires were manufactured. So if you purchase new tires that were manufactured exactly two years ago they will be covered for a total of six years (four years from the date of purchase) as long as you have your receipt. If you lose your receipt, your tires' warranty coverage will end five years from the week the tire was produced (resulting in the tire manufacturer's warranty coverage ending only three years from the date of purchase in this example).
I am not disagreeing with anything already posted, however I will add a few things I have picked up over the years. I have an accelerometer that allows me to do skid testing of various vehicles from sports cars to concrete mixers to be able to determine braking abilities for crash reconstructions.
Consider this my $.02 vs hard facts. After reading the above posts I get the idea (if i did not know any better) that the higher the treadwear the better the tire. I disagree with that idea.
Government ratings are like any other government test. They have a purpose in making a comparison between products but they can be very misleading as well. For example, treadwear ratings. A 700 rated tire should out last a 400 rated tire, however there are multiple ways to do that. Good tires like Michelins can do it because they make good tires (hang with me here for a second). A lot of the cheap, off brand, (bad) tires I have tried can also get a 700 treadwear rating as well. The biggest difference is in the amount of traction they offer.
In simple words you can walk a lot farther on a set of bowling shoes than you can on a pair of running shoes before they start to wear out. The number of people who brag to me that they got 60,000 miles out of a "cheap" set of tires, and they don't understand why anyone would buy a "good" tire is staggering. I currently have a set of Michelin Hydroedges with a treadwear of 800 and they will out perform (even in dry weather) "cheap" tires with treadwears of 400 or higher because of the rubber compound and design. The biggest difference for the average driver who wants mileage vs performance is pretty simple. In the case of an unexpected event happening in front of you where you need to do a panic stop, the difference between the 700 and 400 can be impact or avoidance. This is especially important for young drivers who don't have the experience to look ahead or pay attention to what matters on the road.
Maybe that is why the traction rating is for wet weather and not dry weather. Having a dry weather wear rating and a wet weather traction rating gives you the impression that an A rated traction tire is better than a B rated traction tire. For an extreme example of this, my Hoosier race tires are DOT approved (as required by rules) but they say "for competition use only" right on the sidewalls. To pass DOT rules they only run 2 rain channels and that's it, the rest of the tire is basically a slick. These tires have a treadwear of 50 and a traction rating of B. By looking at the tire you would think the tire is a piece of crap since the ratings are worse than the local tire store brand. However, I can guarantee the Hoosiers will out stick any regular (obviously excluding the other DOT approved competition tires) street tire in dry weather.
In other words. Yes the ratings are valid and the above posts are correct. Just don't think a tire with a treadwear of 200 or 400 is "worse" than one with 700 or 800. It all depends on what you want the tire to do and how much you enjoy driving on "bowling shoes" or "running shoes".
With the exception of the Hydroedges (I wanted to see how they worked) which are (arguably) at the top of the tire food chain, I normally do not run a "cheap" tire with a treadwear over 500 or so as I have found them to lock up way to early since they just don't bite like lower rated tires. As someone once asked me. "Do you want to enjoy driving on a set of tires for 20k- 30k miles or hate driving on a set for 60k".
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08:56 AM
Lambo nut Member
Posts: 4442 From: Centralia,Missouri. USA Registered: Sep 2003
A control tire is assigned a grade of 100. A tire with a grade of 200 can be expected to last twice as long as the control tire, while a tire with a grade of 80 is normally less durable.
And here is the biggest problem with the tire ratings system.
The control tire, is determined by each manufacturer. Say Goodyear picks one of its line or tires to test, it picks a control tire, to base all the others they test from. Same with each of the other manufacturers. So, unless each manufacturers control tire, is exactly the same as the others, the rating don't mean squat from manufacturer to manufacturer. The ratings system, are only relevant to all the tires tested in that line, by that maunufacturer. Even more confusing, huh? This is how, say a Micheln tire with, a 150 rating, could, and usually does out last, say a Douglas xtra trac tire with a 220 rating. The harder the tread, the longer the wear. The softer the tread, the better the traction, but wears faster. Bottom line, you can only use the tire ratings to determine the tread wear, when looking in the same manufacturer.
Kevin
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10:47 AM
Primaris Member
Posts: 550 From: Oak Grove, KY USA Registered: Aug 2001
There is also nothing stopping the manufactures from stamping a tire that is actually a high tread wear at a lower tread wear rating. ex: 400 tread wear stamped at 220 tread wear. They do this as some consumers think a lower tread wear means a stickier tire.
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12:03 PM
SCCAFiero Member
Posts: 1144 From: Boca Raton, Fl USA Registered: Apr 2006
May as well also mention that a tire that comes on a car from the factory will most likely not be the same tire that you can buy over the counter. Even if the manufacturer, model and size are the same. The OE tries are designed with certain traits that will sell the car, not necessarily make the tire have a longer life like the over the counter models will.
SCCAFiero touched on some important facts and Primaris most people can't tell you the first thing about a tire especially what the treadwear number means so I have to disagree there in that usually to a consumer the higher the treadwear number the better the perception and although it's possible it is highly unlikely a manufacturer will purposely put a much lower treadwear number on the tire than it is capable of sustaining. Also any tire that a car is purchased off the lot with can after proper stocking of the market be purchased at most tire suppliers. The current exception due to scarcity is certain run flat tires like those found on some late model Honda Oddysseys which are approved for that one particular tire ONLY from Michelin which has resulted in a class action suit because there is no spare and if you can't find the tire you're stuck.
A little brief about tires since I've sold them for so long; DOT in addition to some other sanctioning body puts out minimum requirements, each tire manufacturer uses their own rubber compound mixture to make their tire and that is probably the single most important factor determining the tires actual wear resistance. As has already been implied, two tires from different manufacturers with the exact same ratings will not wear the same and some high treadwear rated tires are about as tough as wax.
Tires originally installed on a car are usually poor performers in terms of longevity or quality. Imagine the shock I've seen on the faces of people buying 18-19 inch tires for the first time on a new car when the old car had 15-16" tires on it. Tires are the least thing on their minds during the buying process. The OE high performance tires usually get you about 25,000 miles if you're lucky and the lower performers that can get you more often end up cupping causing noise and early replacement. One popular manufacturers tires (whom I will not name) have been nortorious for that.
Most retailers warranty their tires at the point of sale like Sears for example, so the manufacture doesn't come into the picture until after you're gone. The only time they look at the age of the tire is during a roadhazard warranty which is limited to 4yrs of coverage, otherwise if your 50k tire wears out in 25k all they check for is proper maintenance when inspecting the tire; fairly even tread wear. Overall warranty practices depend ultimately on who you purchase the tire from and some will go directly through the manufacturer for approval.
A rating of C on temperature usually makes a sticky tire or did at one point. BF Goodrich (owned by Michellin) makes the Radial T/A which for the longest carried a C rating on temperature and was a very popular tire back when solid white letters were in.
The media caused a big fuss with tire age because that's what they do for ratings, the old tires that i've seen fail did so because they were on the vehicle entirely to long 7-8 years and were visibly in need of replacing long before they failed by delaminating. I would not take issue with a 2 year old new tire unless the age could be seen by color change in the rubber, that in itself does not weaken the steel belts. To my knowledge no real tests or problems have come about as a result of a tire sitting on the shelf for a few years which is probably why there are no regulations in the US for it. As far as Europe goes they have the autobahn with no speed limit and a need for top notch tire condition, which brings to mind the importance of speed ratings that have not been discussed yet.
The speed rating also indicates handling characteristics, the higher the rating generally the more rigid the sidewall and better the cornering. You should not mix speed ratings on the same axle, you should not mix speed ratings on the same car, if you do the higher performing tires should be moved to the rear of the vehicle as a pair. You should not mix directional tires with non directional tires, if you put a directional tire on backwards it will not fail according to a Good Year rep although it will not perform as designed. Otherwise if you have to mix directional tires with non directional I believe the directional pair also go on the rear where you have the least ability to steer in the event of a loss of traction.
[This message has been edited by Joseph Upson (edited 11-22-2008).]
Also any tire that a car is purchased off the lot with can after proper stocking of the market be purchased at most tire suppliers. The current exception due to scarcity is certain run flat tires like those found on some late model Honda Oddysseys which are approved for that one particular tire ONLY from Michelin which has resulted in a class action suit because there is no spare and if you can't find the tire you're stuck.
Maybe I was not too clear about the above, and I have no way to confirm this. I was told by a somewhat credible, inside source, that you can buy the "same" tire off the shelf that came on a car originally. However, it will have different materials and qualities that the car maker required as part of the OE deal. One of the reasons why people seem to complain about replacement tires not being the same as the originals.
Maybe I was not too clear about the above, and I have no way to confirm this. I was told by a somewhat credible, inside source, that you can buy the "same" tire off the shelf that came on a car originally. However, it will have different materials and qualities that the car maker required as part of the OE deal. One of the reasons why people seem to complain about replacement tires not being the same as the originals.
It's possible but not wise, GM and possibly a few others were sued for that kind of tactic years ago since unless the customer gets better than quoted quality, or equipment, it amounts to false advertisement. I'm just going by what I see come and go on a daily basis and although during a meeting earlier this year with four of the major tire manufacturers where in one admitted to having been in need of quality improvement, there was no mention of a difference in an OE tire and the exact same tire purchased elsewhere. If it was crap when it came with the car, I promise you it will still be crap if you buy it a second time.
