Wheels for Competition or Track use

[Luke@tirerack]

For real driving enthusiasts there aren't many feelings that equal the excitement of running laps on a racetrack at their vehicle's limit. And while race tracks were once accessible only to sanctioned races and race-prepared cars, many of today's car clubs and professional driving schools will allow drivers to run their street cars (with relatively few modifications) on the same tracks as their racing heroes. For that matter it is not unusual to have enough track time to drive several hundred miles at a typical club event or driver's school day.

And while its common sense that track use will increase the wear on a car's tires, brakes and shocks, there are less obvious critical components that also wear out ...like wheels! Yes, wheels wear out...or more correctly stated, they fatigue!

Because wheels are so critical to the driver's safety, top racing teams visually inspect their wheels at the track, monitor the total number of hours they are used, and crack test them on a periodic basis. Any wheel that show signs of damage, fatigue or age is discarded and replaced. For that matter Indy Car sanctioning bodies require that their competitors’ wheels meet strict standards when new and that previously used wheels be recertified before 500-mile races.

Unfortunately the same rigorous wheel inspection procedures are not typical for many of the more casual driving enthusiasts who use their vehicles on the track. Maybe it’s because wheels are usually so trouble free that they are often overlooked! But if let go for too long, the results of a wheel failure can be catastrophic!

When it comes to wheel fatigue it is important to remember that it is caused by a combination of the frequency and magnitude of the stresses the wheel encounters. While small stresses can be accommodated for hundreds of thousands of cycles...larger stresses accelerate the wheel's fatigue factor and the number of cycles is significantly reduced. So what is it about track use that reduces the life expectancy of wheels?

Let’s explore some of the factors:

All wheels flex as they are driven through a corner. In normal street driving the amount of flex is minimal. But every corner that is taken at the limit of tire adhesion on the race track causes more flex (remember that today's Track & Competition DOT tires almost match the performance of yesterday's racing tires). It’s the combination of the extra tire grip and extra flex that fatigues wheels faster (and don't forget that spins, ditch hooking the inside of a corner and driving over the track edge curbs each add their own extra stresses).

In normal street driving wheels are typically removed from the vehicle only when the tires are being rotated (typically every 5,000 miles) or replaced (typically every 25,000 to 40,000 miles). But when used on the track wheels are typically removed from the vehicle at the start and finish of each day, as well as, anytime the vehicle's brakes or suspension is being serviced. Additionally DOT legal competition tires wear out and are replaced much more frequently than normal street tires. These extra tire mountings and vehicle installations cause wheel fatigue and also wear the wheel's lug seats and the vehicle's lug nuts/studs or lug bolts/hubs.

So what should track drivers do to take better care of their wheels?

The front and back of the wheels should be cleaned at the end of the every track day and inspected for minute cracks or damage. At the first sign of a crack appearing (regardless of size or location) the wheel should be removed from service and replaced with a new wheel.

Additionally every time new tires are mounted, each wheel should be inspected to verify that it is round and true. If the wheel is found to be bent while the tire is removed, it should also be removed from service and replaced with a new wheel.

Finally if the wheel has been used for an extended period of time, the driver may want to have a local machine shop professionally crack test it in the off season before it is subjected to another year of track use.

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