Overrated Stats
The government requires tiremakers to compare their products with a reference tire, and then self-rate their tires with minimum estimates for how long they'll last (tread wear), how much grip they have (traction rating), and the temperatures they'll survive. You can find this info on the tire, the removable label, and on the tire company's website. Any tire that an enthusiast would consider is capable of earning AA for traction, an A for temperature, and a 400 rating for tread wear. (Because a tire gives up tread wear for grip, performance tires usually last no more than four times as long as the reference tire, which is what the 400 rating means.

It's important to know what all this means, but don't put much stock in these ratings. For one thing, the tiremaker is free to give its tires a lower grade. You might see the same hypothetical tire discussed above rated A for traction, B for temperature, and 200 for tread wear. And often, these ratings aren't consistent within even a single manufacturer. They're an unreliable measure.

Overrated Stats, Part 2
A tire's nominal tread width, aspect ratio, and speed rating appear both on a tire's description and its sidewall. Consider a tire labeled 245/45R17. Section width is the 245 (millimeters). Aspect ratio is the 45—it means the tire's sidewall is nominally 45 percent as tall as the tread is wide. Speed rating is a letter preceded by a number: An example "88Y." The 88 is an assessment of how much load the tires will carry.

Almost every tire an enthusiast would consider will earn a Z (capable of surviving speeds at least> up to 149 mph), a W (up to 168 mph), or a Y (up to 186 mph). Again, this is a safe estimate. It does not mean a Z-rated tire will blow at 151. Indeed, it may survive 190 mph.

Now that you know that, forget about it for the purpose of finding a grippy tire. Here's what you should look at:

When to Stray From the Mainstream
It's hard to go wrong with Bridgestone, Michelin, Pirelli, Yokohama, Goodyear, or the like. However, some of the lesser-known brand names, especially those from South Korea, make some damn good tires. One lesser-known Japanese maker produced a tire that handed it to the big names on a damp track and matched them in the dry.

I've also tested a Chinese-branded tire I'd never heard of before or since that matched the majors. Going this route is a bit like investing in an unknown company: Use money you don't mind losing.

Reach for the Limits
If you're looking for the tallest, widest tire, you might not find it in tire company materials, which publish "nominal" sizes and diameters.

The tire industry association allows tires to fit within a size window, and then publishes the "theoretical size that may vary from the actual size." But don't confuse this with production tolerance! Performance tires are almost always in the upper corner of the permitted window, near the limit of what the tire governing body allows. Using the previous example of a 245/45R17 tire, a serious performance tire would be slightly wider than 245 millimeters, with a sidewall taller than 45 percent of 245, and an overall diameter greater than the 25.7 inches published in the spec sheet. To find the performance tire you want—the one that nudges right up against the upper limit of what your car can use—you might just have to get out your old-fashioned tape measure.

Ask Around
You may have to call the tire company to confirm what's the best tire for your very specific need. Find a general number and ask for product marketing. The poor guy probably used to be a test driver and would love to talk fast driving.

Also, check out the customer reviews on the websites of the big Internet tire sellers—but be wary of what you read. This is a good place to find useful information from people solving the same problem, but it can also host a lot of misinformation from buyers who aren't experts.

In our continuing example, the Michelin Pilot Sports intended for the Viper that I put on the Mustang were radically different from those designed for a Porsche 911 Coupe, and those had some notable differences from those intended for a Chevrolet Corvette. (You'll see this when one tire size is listed two or three times, with different multiple part numbers in tire company specs.) While the Viper owner may praise the tire in his comments for its extreme grip, the Corvette driver may be upset because his Pilot Sports lasted "only" 30,000 miles.

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