Measuring tire wear is critical to handling

By Larry Cothren, Stock Car Racing
July 26, 2001
1:44 PM EDT (1744 GMT)

Is the race car loose? Is it tight? Does it have too much camber? Too much air pressure? These questions and more are answered by Winston Cup tire specialists who measure tire wear during races or during practice sessions.

The gauge is a critical device for measuring wear.

The tools of the trade are basic ones -- a gauge for measuring the actual wear, a torch and a good scraping tool, when needed for scraping away rubber buildup, a good note-taking system. A tire specialist puts these tools to use to give data to his driver and crew chief in their search for a well-handling race car.

Tire specialists rely on wear pins -- which appear as tiny dimples molded into the tires -- to measure tire wear. The wear pins, about 3/16 inches in diameter, are spaced five to a row across the width of a tire. Gauges used to measure wear are incremented in 32nds of an inch.

Rob Lopes, tire specialist for the No. 1 Pennzoil team of driver Steve Park, says the key is to mark a particular set of wear pins so the data obtained is accurate.

"Most teams will get a pre-wear measurement on sticker (new) tires," Lopes said. "They'll get a measurement on the wear pins across the tire and mark that set of wear pins, with, say, an arrow or a triangular mark on the sidewall, and go back to that same set of pins after they use the tire.

The wear pins run across the tire's width.

"It's important to mark a particular set of wear pins when you pre-measure, then go back to the same set, because the measurement isn't always consistent around the tire, as far as depth goes."

The readings help a team decide what adjustments to make on a practice session or pit stop, and when they need to make a pit stop.

"When the tires come off, all the data is recorded -- buildups, temperatures, etc. -- then you'll get the torch out, or if the tires are hot enough you don't even need it," Lopes said. "You heat up the rubber buildup and scrape it from around the wear pin that you've pre-measured; then you'll take a post-run measurement, and that gives you your tire wear.

"At that point, really, you're just trying to keep track of what your tires are doing. You can also get a reading on if your car is a little loose or a little tight, by your tire wear. Most of your camber (how much a tire is tilted inward or outward) decisions and such will be done off your tire wear during practice."

Tire specialists sometimes use a torch to scrape away excess rubber before checking wear.

A tight race car will likely show excessive wear on the right front tire, with the tire looking like it's feathered across the tread patch. A loose car, meanwhile, is more apt to show excessive wear on the right rear.

The same rules apply to wear on racing tires as passenger car tires: When a tire has too much air pressure, it will show excessive wear in the center; too much camber on the front tires will show wear on the inside of the tire, etc.

A new tire will have approximately 3.5/32 of an inch of rubber, Lopes said.

"That doesn't sound like a lot," he said, "but when you put a hundred miles or so on your tires and you're still showing 1/32 of rubber left, yeah, you've taken off two-thirds of what you've started with, but there's still enough there to keep you in a safe realm where you're not riding on fabric, on the belts that are underneath the tread."

NOTE: Larry Cothren is associate editor for Stock Car Racing magazine. For more technical and general features on all levels of stock car racing, pick up a copy of Stock Car Racing magazine, or visit www.stockcarracing.com.