From: Tim Malzahn <tmalzahn@tnmnetworks.com>
Date: Sunday, April 25, 1999 10:06 PM
>When I was changing the tires back to the streets, I could not get one of
>the right front lug nuts loose. So I did not change one of the tires for the
>trip back home. When I got home, I ended up shearing off the wheel stud
>trying to remove the lug nut.
>I think what may have happened is when I was torquing the nuts down this
>morning, I weakened one of the studs enough so that it actually broke
>sometime in competition during the day (last run.)
<< It's also possible you cross-threaded the lug nut while you were changing
tires. Even when you swear you've been *really* careful, it happens
sometimes. >>
Even more likely was improper torque. We have had a couple broken studs, and
it turned out they were torqued over 250 ft lbs. That was what it took to
break the others loose. 90 ft lbs does not feel like alot on a large cross
wrench, or evenan 18 inch breaker bar. We should push more about the use of a
torque wrench when tightening lug nuts. Over tightening is almost as bad as
under tightening. We have had two wheels come off at events that I can
remember here (About 12 years). One was a broken stub axle on a formula ford,
and the other was loose lugs on a prepared Z car. There was no further damage
to the FF, but the Z did have a bit of crunched body work as the tire came
off. But there were no injuries, so we got lucky, and should make sure this
does not happen again.
<< Properly torquing the lug nuts down shouldn't weaken the studs. The only
evidence I can claim is years of changing tires two or three weekends a
month using this method -- the only wheel stud failures I've ever had were
due to cross-threaded lug nuts. >>
Cross threads do happen, but more often is wrong torque. Stretching the stud
even a fraction each time will ent up with a failure sooner or later. Cross
threading usually will not get tight as it is happening, and should be
obvious in tech. These are things that should be looked at.
I put all new longer studs in my car, and had them torqued to 100 ft lbs.
They were not fully seated, and after a 4 mile drive I felt some shaking,
pulled over to find almost every lug came loose. I had to torque to 150,
drive, torque, drive, etc. Finally they seated fine, and I now run 100 ft lbs.
Gary M.
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