Recently i’ve seen amazing scientific advancements such as liquid body armor, frozen smoke, and somewhere plastic that ‘fixes itself’ after being dented, so I was surprised tonight to see tread coming off of tires during NASCAR races and cars stopping semi-frequently for complete tire changeouts.
What’s holding us back from creating tires that last for an entire race?
I’m not a racecar driver, or otherwise affiliated with racing, but it’s my understanding that the tires are designed to wear down in that way, so as to provide better traction. The tire sort of glues itself to the road, which necessitates leaving a little rubber behind on each revolution. They could make the adhesive layers thinner, but that would presumably decrease traction, and they could make the whole tire thicker, but that would be heavier. Presumably, they’ve weighed the speed cost of the tire changes against the cost of the extra weight and traction, and found the optimum formulation and thickness for the tires.
Chronos basically has it right. The tires are soft because they grip the track better that way. When you’re going ~200 MPH, you want a bit of traction under you (especially running four wide in the turns, as they are today). This softness causes them to wear down after a while, and rather than ride on the axels, they figure it would be better to put a new set on.
Now, I wanted to comment on the bit above. They’ve actually found that different tires work better for different tracks. “Harder” tires last longer, but give less traction. “Softer” tires give better traction, but wear down faster. Oftentimes the individual cars will even change tire pressures in the middle of a race due to changing track conditions.
I’m not a big NASCAR fan, but I watch it occasionally. I imagine someone more informed will be along shortly.
Not only that, but the “speed cost” of tire changes is near zero. Cars have to pit for fuel on a pretty regular basis, and tires are normally changed simultaneously.
I would just add that tires usually come apart entirely because of an outside force other than the road. Like the fender rubbing, or another car hitting it, or hitting debris. Not just from regular wear.
Like everybody else has said, there’s (broadly speaking) a tradeoff when designing tires between high grip and long life. Again speaking generally, a softer tire will be “grippier”, enabling faster braking, cornering, and such, but it will wear out quicker than a harder one.
Simply making the tread thicker only works to a point, and I believe heat is the main limiting factor. Heat buildup comes (primarily) from the flexing of the tire as it rolls - a given segment will flatten slightly as it comes in contact with the ground, and then will round out again as it comes up. The amount of heat is pretty much proportional to the amount of material there, while the rate at which that heat is dissipated is basically proportional to the surface area. Thickening the tread increases the heat buildup rate, while doing nothing to increase surface area. Go too far, and you’re asking for problems.
Tread squirm is also increased when it’s made thicker. Which is a bigger factor, I don’t know.
Another reason is that cars have to come in to refuel periodically, anyway. (Partly because size of the Nextel Cup fuel cell is limited by rule, so it could be argued that this is an artificial constraint. Nevertheless, it’s there.) If you’re stopping anyway, might as well change the rubber - if you don’t need to, you’re probably using tires that are too hard, costing you speed.
Or something like that. It’s an interesting optimization problem (What tire choice/fuel loads allows us to run the race fastest?) complicated by many factors. Do Nextel Cup teams have multiple choices of compound to choose from at each race, or does Goodyear bring only one?
Formula One is arguably more interesting, as it has a two-manufacturer “tire war” going on. Michelin and Bridgestone are competing something fierce to be the quickest tire, so they’re less inclined to “play it safe” and are very aggressive (and soft) with the tires they provide. Goodyear simply needs to avoid legion tire failures in Nextel Cup, as they’re really competing against no one.
Nextel (Winston) Cup tires wear out very easily. Depending on what tire Goodyear brought to the race track that weekend (all teams use the exact same tire compound), they could last most of the afternoon (well, left sides, anyway) or they may burn them off in 30 laps.
Track composition is a big part of it. Tracks like Rockingham and Darlington are incredibly abrasive, and will literally chew the tires apart in just a few laps. New pavement will also wear tires heavily. Concrete (such as at Bristol and Dover) will wear lightly (it’s not uncommon for teams to leave left sides on for 150+ laps).
Speed also severely impacts tire life, especially with the thin sidewalls that NASCAR tires have. (Thinner sidewall = less weight, more flex to spread the contact patch out across the tire.)
Another factor is that NASCAR tires wear unevenly. Product of the racing. The unchanging direction and relatively unvarying speed means that the right side tires wear much more than left side tires. Because of this, the right sides will wear out faster.
In most racing series (including NASCAR, I think, although I’m not 100% sure), tires don’t have tread. The only reason your street tires have tread is to cope with rain, forcing water out through the gaps so the rest of the tire remains in contact with the road surface. If the road surface is dry, those gaps only reduce the tire’s contact patch. Since racers can switch to rain tires if it starts to rain (or stop the race, in case of oval tracks), they run slicks–no tread.
A couple of years ago, Formula One mandated tires with four treadlike gaps specifically to reduce grip and hence speeds.
Having changed a racing tire or three over the years, let me add that when people talk about sticky tires they are not kidding. When a racing tire get to operating temp the surface is actually sticky. Man do they hang on, but boy they do wear quick. This is why when race cars are on the parade lap they tend to weave back and forth. The are trying to get the tread up to temp before the green flag drops.
I didn’t know the tires got sticky. Thats moving pretty fast 
Can’t they throw some kevlar in the mix?
It’s true about the stickiness, and you don’t have to be going all that fast, either. I like to put relatively soft tires on my car for grippiness, and last year I had the opportunity to drive it on a racetrack. It being my first time on a racetrack, I wasn’t breaking any speed records, but after 4 or 5 laps (on a 2.25-mile road course), my tires were noticeably sticky and warm when I parked the car.
