Driving is a simple joy, and many expand that passion with the exhilarating thrill of racing. Gone are the days when most racetracks were limited to professionally tuned racing vehicles. With the expansion of car clubs, and driving schools, many drivers are now able to expand their knowledge of high performance driving with their street cars. Using stock or limited modifications, drivers can now race on tracks driven by many top professionals. While logging laps, it is typical to assume the increased wear on suspension components, brakes, tires etc. Often forgotten are other crucial parts that wear, like the vehicles wheels. Wheels will actually fade over time as well!
The wear on the wheels and the vital importance of them for driver’s safety is often overlooked. Most race teams will scan and inspect their wheels throughout the race weekend. Typically the hours on the track are monitored as well, with periodic stress tests being performed on the wheels. Upon inspection, race teams will determine if the wheel is fatigued, determine if it is past its prime and remove and replace the wheel. The disadvantage for the “weekend racer” driving enthusiast is that these checks and balances are not performed. Because the wheel is not thought of as critical component they can fail over a period of time, mainly because of the higher G-Forces and higher impact on the wheels from the grind on the racetrack.
Understanding the stresses involved on a wheel is vital to grasping the difference between your daily commute, and a hot lap around the track. Daily driving can account for minimal stresses over the rotational cycle of a wheel, while on track use can increase the level of stress over shorter periods of time. You may ask what this added stress from track driving is.
During normal street driving wheels will flex when going through a corner. Combine that with standard street tires, and the flexing of the wheel can be minimal. Now add DOT approved competition tires, which are virtually similar these days to the racing tires of yester-years. Competition tires now are much stiffer, and provide much more grip, which in turn create much higher lateral g-forces than regular street use tires. Race tires also transfer more of the stresses and flexing of a turn directly to the wheel. Cutting the apex of a turn on a track compared to a slow roll around a street corner greatly adds to the fatigue of a wheel.
Now also add in the limits you push when driving on the track - cutting those corners ever so tight, sometimes pushes you up the edge curbing, or trips on the track rumble strips. We all get a little loose on the track too, spinning out and maybe experiencing an over-run off the track. Add in the extreme temperature changes from braking, going from S-turns to hairpins, the constant fluctuations from ambient temperatures to the extremes of brake heat. All of these forces from the track greatly increase the rate of wheel fatigue.
One last factor involved in wheel fatigue is the rate at which a wheel and tire combination are mounted and dismounted. Many street tires have a longer life expectancy in comparison to DOT legal competition tires which degrade faster. Depending on the frequency of track days the replacement rate of the tires can be more frequent.