There are several possible reasons for breaking wheel studs, but usually it can be tracked to being either over-tightened, under-tightened, or not fully seated. As Steve pointed out, you need to retorque new aluminum wheels several times every 40-50 miles or so (unless it's being flogged, then more frequently) until they hold their torque values due to the conical seat on the lug nuts work hardening the conical taper of the seating surface on the wheel. I'm guessing it was torqued to spec for the wheel stud size when it left and then as the wheel material contacting the lug nuts yielded, the torque was lost. Once the studs are loose, they fail remarkably quickly and with minimal loading. Have you calibrated your torque wrench lately?
Too little thread engagement will usually lead to stripped wheel studs, not broken studs, but you do want at least 8 turns egagement as a general rule. It's possible that you received a bad batch of wheel studs, but not all that likely in my experience. Hydrogen embrittlement caused during zinc plating can compromise wheel studs, or any plated high-strength fasteners for that matter, but they're supposed be baked post-plating in order to release any captured hydrogen. If the wheel studs are not electro-plated, then that would rule out that possibility.
Tobin
KORE3
|