I sheared a wheel stud off at a track event on Sat. I'd like to better understand potential causes. Speculation at the track by most was that it was likely caused by wheel flex.
- I'm running Kumho 710s (275 rear, 245 front)
- Rear passenger side wheel stud sheared right off (only one)
- I'm running ARP extended wheel
- I'm torquing lugs to 80 ft/lbs
- Wheels are Volk CE28s

Not sure where on track it happened. Could not feel any difference in the car. I noticed the stud was sheared in my standard walk around the car after a session check.

Thoughts?

 

If you didn't feel the wheel wobbling, then it wasn't wobbling enough to break a healthy stud.

If you have the stud, somebody with some expertise can look at it and give you some ideas about how and why it broke. But over the internet, not so much.

 

Wheel flex was described to me as not a wobble, but the wheel actually flexing so much under load that it shears the stud or multiple studs.

 

You would have felt it.

 

It was probably overtightened which means it was stretched beyond the yield point then snappped. There are really two failure modes, the wheel's loose and snaps the studs, the studs are overtightened and damaged and can break at any time. Once a bolt's tightened beyond it's elastic stage, it's deformed and weakened.

Common cause is people checking lug torque right after coming off the track and tightening them hot. When they cool down, the effective torque goes through the roof and the studs are damaged. I always check right before going out on the track, not when hot.

If you let people put wheels on your car, they often just crank them on with air and damage the studs too.

How's wheel flex supposed to break the stud anyway? I've seen the whole center sections of wheel break free from the rest of the wheel at the track but, the studs still held the center section in place.

 

Torque wheels COLD!

 

Yes, I always torque the wheels cold.

I guess the "wheel flex" explanation is not likely. Irritating if it's just from the stud getting weakened from shop using an air gun and overtightening.

 

Most likely culprit is whatever trauma happened to that stud when it was pressed in or when the lug was torqued....however, it shares the load with 4 other lugs, so it would have to have been crazily overtorqued.

Bearing may go out soon and one by one all the other lugs will fail in the process. My first rear bearing went out after 6 or 7 track days. Lugs were ALWAYS torqued properly.

 

One common thing I've seen too is, if one lug snaps, the rest are on the way. Are you pointed out, it's unlikely only one was damaged. I'd replace them all on that hub when you get ready to replace them.

 

Yes, they will all be replaced. Should I replace bearings at the same time?

Car is seeing at least two track days every week. There's only been 3 weekends since first of May that I haven't been at the track.

I've been searching (without much success) for information on preventative maintenance checklists. I'm doing the obvious stuff like fluids, checking suspension components, etc. What I'm looking for is more info on major items that need to be inspected or replaced regularly. I've already had the control arm mounting points up front reinforced.