There are as many opinions on autocross tires as there are people who autocross. Our goal here will be to give you some generic information that should apply to everyone. What kind of tires should you buy? Well, that depends on your goals and intentions, as well as your budget. There are at least three categories that you might fit into:
You aren’t out to set the fastest time of the day, you just want to have fun. Your budget doesn’t allow for you to buy an extra set of wheels and a set of dedicated sticky autocross tires, or you just don’t want the hassle of changing tires for every autocross. If this describes you, there are lots of high-end “summer” performance tires, sometimes called “ultra-high performance tires”. Unlike those people who are looking for a tire that will get them where they’re going for 5 years or 80,000 miles, you want to look for something that is geared toward performance. You’ll most likely want a Z speed rating or better. (high speed-rated tires generally have stiffer sidewalls and will offer greater steering response) And you’ll want something with a fairly LOW treadwear rating, generally 200 or less. This gives you a tire that will wear more quickly, but should offer MUCH more grip than it’s all-season, H-rated, all-season cousins. You’d do best to ask around to see what the current hot street tires are, because there’s always something new… or something not-so-new, but available at a great price.
You want to be in contention for the fastest time of the day. You don’t think you can generate enough G’s on street tires to have any fun. You want to compete in larger events (such as offered by the SCCA) and be capable of winning. You can afford an extra set of wheels and tires, don’t mind changing them, and don’t want to scuff up your street tires. If any of the above describes you, then a set of “R-compound” autocross tires is the thing for you. There are several brands to choose from. All are “DOT approved” for street use, but most come with warnings to NOT drive them on the street. (though some people do, anyway) They are ultra-soft and sticky, and made specifically for the purpose of autocrossing. If you did drive them on the street, you’d be lucky to get 4,000 miles out of them. Used strictly for autocrossing, depending on which tires you buy, what car you put them on, how you drive and what surface you drive on, you can expect to get anywhere between 50 and 100 runs out of a set. Again, ask around as to what the current best options are.
Run what ya brung! You can have fun autocrossing ANY car on ANY tires, and you can learn a lot doing so. In fact, the traction limits of “crappy tires” will be so low as to be very easy to find. If you can teach yourself to drive at the limit of those tires, the same techniques will apply to a grippier tire. You’ll be doing the same thing, dancing on the edge of traction, just doing so at a higher speed. So, as long as your tires have some tread and hold air… come on out and have some fun!
But what size of tire should I get?
Don’t I want the widest tire I can get with the lowest profile? Well, yes and no. You want the widest tire that will fit your wheel and not have clearance problems on your car. Tires that rub fenders, suspension parts and fender liners are not a good thing. Low profile? This is one of the many compromises you will have to decide where to go with. Lower profile, of course, gives less sidewall and greater steering response. It also takes away much of the tire’s ability to absorb road imperfections, which can negatively affect handling on a rough surface, or worse yet cause a bent wheel if you hit a big hole. Most autocrosses are run on parking lots, many of which are far from smooth. With that in mind, you don’t want EXTREMELY low profile tires for autocross. Unless your car fits extremely wide tires (like 275 width or greater), you probably want to stick with a 40 to 60 profile tire. You should aim to keep the overall diameter of your replacement tires as close as possible to the diameter of the orginal tires, perhaps slightly smaller. (going smaller will improve the effective gear ratio and provide quicker acceleration… while lowering the top speed acheivable in each gear) One more time, it’s best to talk to people with experience autocrossing the type of car that you have to get specific advice.
Okay, I’ve picked a set of tires, now what?
If you bought them online, you’ll probably have to find a place to mount them for you. If you bought tires for autocross only that will not see street use, do you need to balance them? Not really. You’ll rarely get them above 60 mph, and even if they were out of balance, you probably wouldn’t notice it while driving an autocross. But what about tire pressure? Without knowing what tire you chose, we can’t even guess. If you can’t find any good advice for your particular tire/car combination elsewhere, a good place to start might be about 5 psi less than the maximum pressure stamped on the tire. From there you can use the old autocross trick of marking the edge of the tread at the sidewall with shoe polish or chalk to determine how much roll-over you have and adjust pressures accordingly. Or, if you want to buy or borrow a tire pyrometer (a thermometer for taking tire tread temperatures), that is the best way to determine correct tire pressures. Your goal should be even temperatures across the tread of the tire. And don’t forget to get a precision alignment to get the most out of your tires.