> Chances are it's just that you really should re-torque after a few hours
> of driving. But when I put on my sticky tires I want the wheels to stay
> on all day, so I go five pounds over. Since I've been doing that I have
> never had any motion when I re-torque.
>
>   =20
Certainly is a good practice to check torque after a few miles, but for=20
most drivers, quite inconvenient.
> And that may explain why tire shops regularly overtighten - they don't
> want a nut to come loose and they don't care if they warp a rotor/drum.
>
>   =20
The poorer quality workmanship shops probably as a cost savings. The=20
Goodyear dealer chain that I usually go to uses "Torque Sticks".
http://answers.yahoo.com/question/index?qid=3D20060705192044AAt9HBD
Though it says not a replacement for a torque wrench.
I have found 100% of the time there not to be a loose or overly tight=20
bolt. I have to admit, I do not use a torque wrench on my wheel bolts,=20
but use a calibrated human arm. :)

There are bolts used in vehicles that are one time usage, cylinder head=20
bolts being one of the common areas. These bolts are stretched during=20
installation, and their characteristics change with the stretch. They=20
also probably have a special lubricant, and should not be oiled unless=20
the shop manual directs to be.

It's interesting in the structural engineering world of building/bridge=20
construction, the torque wrench is not the preferred method of=20
tightening bolts since the late 1980's. "Turn of the Nut" method is the=20
generally accepted method, where the nut is tightened to a snug=20
condition, and then given an extra specified rotation, depending on grip=20
length, bolt size, etc. Typically 1/4 to 1/2 turn more. If a torque=20
wrench is to be used, then a device that measures the bolt tension is=20
used to measure the torque necessary provide the required clamping=20
force. This must be done for every batch of bolts, and if the=20
lubricant/condition of the threads changes, must be done again. My first=20
job out of college was field engineer on a large bridge project where I=20
had a 7' long torque wrench, and checked bolts 180' in the air for=20
tightness.
--=20
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