There’s a lot I don’t understand about car culture, motorsports, and racing. Help me out.
In the USA, the National Highway Traffic Safety Administration (NHTSA) created the Uniform Tire Quality Grading (UTQG) as a means of assessing the tread life, traction, and temperature range of tires. The tread life is supposed to be calculated by driving 7200 miles on some public roads in Texas and comparing the wear of a test tire to that of a reference standard. I say supposed to because nobody checks. UTQG ratings are provided by manufacturers, not an independent standards body. That means manufacturers can label them with whatever rating they want (subject to a fine if they abuse the system). Interestingly, the coefficient of friction of a tire is supposed to be described by the following equation.
Let’s see a few examples.
- 40TW – 1.288G Hoosier R7
- 100TW – 1.123G Nitto NT01
- 200TW – 1.012G Bridgestone Potenza RE-71R
- 300TW – 0.952G Michelin Pilot Sport 4S
- 400TW – 0.912G BFG T/A Radial
- 500TW – 0.882G Pirelli Cinturato P7
- 600TW – 0.858G General Altimax RT43
In the Car & Driver “Gumshoes” article, C&D test 5 tires in the 300 treadwear category. On a 200 ft diameter skid pad, they register from 0.90 to 0.95G. That’s in the expected range of 300-400 treadwear. They also show a 50-0 mph stopping distance from 79-82 ft. That can also be converted to Gs, which comes out to 1.02-1.06, which is the range of 200 treadwear. They also showed values for wet skid pad (0.75 – 0.83) and wet braking (0.77 – 0.88), in case you’re interested.
The 200 treadwear segment is particularly popular because various autocross organizations and endurance racing series have standardized on the 200 treadwear number. Due to the weird popularity of autocross, a number of tire manufactures are having a war to see who can make the stickiest 200 treadwear tire. Ask people in the know and you’ll find there’s a lot more information about each tire than a number stamped on a sidewall. Some tires are grippier than others. Some are more durable than others. Some are better in the rain. Some like to be run at high pressures and others low. Some squeal more than others. And yet somehow they are all 200s.
Among the 200s there are 3 main categories.
- Autocross – come up to speed quickly, don’t wear very long
- Endurance – consistent speed and longer life
- Cheap – not as grippy or as long-lived as expected
One of the most popular autocross tires is the RE-71R. Various tests show that it has the grip and lifespan very similar to an NT01, which is a 100 treadwear tire. I’ve used them and find that they are the most heat resistant tire I’ve found. Which is to say I’ve melted every other tire.
The most popular endurance racing tire is the Hankook RS-4. When the Lucky Dog Racing League made that their official tire, it wasn’t that big of a change since most teams were using them already. The grip is consistent from new to cords and they last around 3 times as long as an RE-71R.
The cheapest 200 might be the GT Radial Champiro SX2. This is the series tire for some GT86 organizations. It’s less sticky than the typical 200. The Federal 595 RS-RR is another inexpensive tire. It’s nearly as grippy as the RE-71R and even less durable. I’ve used them several times and I like them okay.
The only reason I really care about UTQG and 200TW specifically is because I race in series that cap performance at 200TW. But I’d much rather be on harder tires. Less sticky tires are cheaper and more durable. They also reduce the wear and tear on every other component and even reduce fuel usage. Aside from the economical reasons, I have more fun driving on slippery tires. The fastest teams are still going to be the fastest teams regardless of the tire, so why can’t we race on all seasons? One reason is heat. Some all season tires don’t manage heat well. The same is also true of 200TW tires. We eventually figure out which ones do and don’t work and gravitate towards the models that work well. It wouldn’t be much of a change from that perspective.
In my dream world of racing on all season tires, I wouldn’t specify a treadwear rating. Manufactures can game the system and label their tires however they like. So there would need to be a list of allowed tires and a standards body testing them to ensure they fit within some parameters.