Durometer Readings, Treadwear Ratings, And DOT Tire Traction

Tires provide the critical link between a race car’s setup and the track surface. Teams, especially the pros, focus heavily on tires because they can make or break a good setup. However, on the flip side, a great set of tires won’t make a lousy setup look good, according to Duane Sampson of Yokohama.

“It’s all part of one big equation,” Sampson said. “If you had a great tire and a terrible suspension setup, there is only so much a great tire can accomplish. The same thing [can happen] if Joe B. Racer is in a bad mood — if he’s mashing the throttle, driving the car, and asking the tire to break the laws of physics, the tires don’t matter.”

Many racers view tire selection, particularly when restricted to the DOT-legal variety, as more of a black art than a science. DOT tires come with several ratings and racers can measure several aspects of the tire. However, what does it all mean, in particular, durometer readings and UTQG treadwear ratings? We asked the experts from Hoosier Racing Tires, Toyo Tires, and Yokohama Tires for their thoughts.

Durometer and UTQG ratings are largely going to depend on what you are asking the tire to do for you.

Durometer Readings

When you durometer a tire, you find the hardness of the rubber. That’s a fact. However, does a softer tire provide more traction? That depends.

“Two different model tires can react differently as you drive on them, even if they start with the same durometer reading,” said Toyo’s Product Manager of Competition & Specialty Tires, Cameron Parsons. “Many different chemical compositions are making up the tire compounds that exist in the market. There is no set compound for a 200 UTQG tire or a racing slick across the market; every manufacturer develops its own special chemical makeups to achieve its performance goals.”

Yes, one is a rain tire and one is a slick. These two tires have the same treadwear rating — they might even have the same durometer — but, they definitely don’t have the same grip in each other’s weather conditions.

Generally speaking, a durometer reading tells you how quickly a tire reaches optimal operating temperature. The softer the compound, the faster it comes up to temperature. However, the durometer reading won’t tell you what that optimal operating temperature is.

“When a tire activates depends on a lot of variables, in addition to its durometer reading — the car’s weight, how much downforce it has, driving style, track temperature, type of surface — those attributes make a difference in how quickly the tire comes up to grip,” said Business Unit Manager for Circuit Racing at Hoosier Racing Tire, Adam Batton.

Terry Wolfenbarger, of National Auto Parts Tire & Auto Repair, Knoxville, Tennessee, demonstrates the usage of a durometer.

The durometer reading also provides a window of time when that tire operates best.

“If you’re doing an endurance race, and it’s a soft tire, you start off super-fast, but that compromise will come up later in the race when the tire degrades,” said Sampson. “If you have a medium or hard compound, it’s a little slow to start, but you can likely use the tire more aggressively in the later stages of the race.”

A durometer comes in handy when you have a rack of used tires, and you want an idea of how the tires were used (or abused).

“I can better tell via durometer reading that, maybe, the inside of the tire is totally smoked,” Sampson said. “But, a durometer is not the best method, as it is all ‘after the fact,’ and hopefully goes hand-in-hand with your race notes. I’d much rather have someone use a pyrometer [to obtain] temperatures right after the session, jot it all down in a cohesive manner, and keep notes with the car and tires, rather than try to sleuth out which tire to use again via durometer readings months after the tires were used last.”

A lot of people might think of Sprint cars when they think about a durometer. Heat cycles on those big meats can change the durometer of the tire quite a bit. (Photo: Bobby Kimbrough)

When using a durometer, make sure you do so in a controlled environment.

“If you durometer a part [of the tire] that was in the sun versus the shade, the two areas would durometer differently,” said Batton. “If you durometer on the edge of a block or close to a sipe or groove, that will skew the durometer reading.”

Treadwear Ratings

All DOT-legal, passenger-car tires (with a few exceptions) come with a UTQG (Uniform Tire Quality Grade Standards) treadwear rating. Some sanctioning bodies set a minimum-treadwear rating to reduce the number of tires racers go through. However, what kind of effect does a treadwear rating have on traction?

“The primary intent of treadwear testing and ratings is to measure the expected life of the tire — there is no set standard in the industry for how much traction a certain treadwear-rated tire should offer,” Parsons said. “That being said, treadwear generally does have an inverse effect on how much traction the tire provides. But, the UTQG rating is rarely a good indicator of a tire’s performance level. Some tires of a particular treadwear rating today might be much better than a tire of an equivalent treadwear rating from five or ten years ago.”

These are the same Toyo RR tires off of the same car but manufactured at different times. Even if they were brand-new, they could perform differently or have a different chemical makeup. Age and heat cycling play a part as well. Note the smooth shine on the left tire, it is old with many track days on it. It’s not going to grip as well as the one on the right with only one weekend on it.

Furthermore, the DOT does not perform the tests to determine the UTQG treadwear rating. Manufacturers determine these ratings based on results from their own tests or those conducted by an independent testing company they hire. Thus, tires with the same treadwear rating may differ from manufacturer to manufacturer.

“While these numbers are far from meaningless, it should be known that there is a large variety of meaning to these numbers in today’s tire market,” said Parsons. “What might qualify as a 240 UTQG tire from one brand may differ from another brand.”

We used the Bridgestone Potenza RE-71R for autocross last season, which is a 200 treadwear (left). It did a great job but barely made it to the end of the season. This year, we plan to try the Toyo Proxes R88R, 100 treadwear tire, seeing we are running D Prepared.

Nevertheless, treadwear ratings can provide you a rough idea of a tire’s capabilities.

“With an 80 UTQG-rated tire versus a 500, an 80 is going to be a much softer compound that provides more grip,” Sampson said. “If it’s a 300 UTQG-rated tire versus a 320, they’re going to be pretty similar. Most would be hard-pressed to tell the difference based on [UTQG treadwear rating] alone.”

The Best Way to Gauge Traction

Okay, so durometer readings and UTQG treadwear ratings can provide some idea of how a DOT-legal tire performs, but it’s far from conclusive. Racers can call manufacturers to help select the appropriate tire for the application. But, for a more definitive approach, experts recommend doing some investigating for yourself.

“It boils down to putting tires on your vehicle and trying it firsthand or collecting feedback from other people’s experiences,” said Batton. “You could send a tire to a high-quality research facility that measures force and moment data, but other tools, such as a durometer, are more practical and should be used simply as a reference.”

Taking simple notes with the date, ambient temperature, starting air pressures, ending air pressures, and tire temps can help you determine if the tires are working to their potential.

If you put different tires on, make sure to take detailed notes, and store those notes in a safe place for future reference. When you try new tires, make sure to keep everything (setup-wise) the same for a run to minimize the testing variables.

“Document all you can,” Sampson said. “Before going out, take cold tire pressures, ambient temperature, and track temperature. Once the car comes in, get driver feedback, hot tire pressures, track temperature, and inside, center, and outside tire temperatures with a probe rather than an infrared pyrometer. The probe takes a more accurate tire reading as it focuses on the tire, specifically the cords, and the variances of an infrared could also be picking up the engine or brake heat.”

As you can see, there is no definitive answer to tell the best tire for you. So many factors play into a tire decision:  Driving style, car setup, weight, temperature, surface, and even the chemical makeup of the tire itself. You can use a durometer and the UTQG rating to give you an idea of how a tire will perform, but it’s up to you after that to research, fine-tune, and try out different setups to see what works best for your situation.

Treadwear rating will not tell you the amount of grip a tire has. Consider it as a guide, but not the definitive reason to purchase. It looks like you’re just going to have to test all the different ones to find out which is your holy grail tire. Happy hunting!

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