Miata Mailing List: August 1994, Message #262
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   From: jwa@yog-sothoth.dcrt.nih.gov (James W. Adams)
Subject: Re: your mail
   Date: Mon, 8 Aug 1994 16:58:58 -0400

mjb@vince.arl.mil epistolizes:
> 
> About this whole lugnut torque thing, the problem is not just because
> the dealer happened to use an air wrench.  The problem is improper use
> [...]

Tom was quoting me, and I wasn't referring specifically to lug nuts,
although it is perfectly possible to step-torque wheels with an air
wrench.  As you say, many people do abuse these tools.

On the other hand, I'm not convinced that, except in the most extreme
circumstances, brake rotors are going to warp due to the way the lug
bolts or nuts are tightened.  Warpage is much more common in cases where
a car with hot brakes is driven into deep water than from most cases of
lug nut abuse.  The brake rotor is a hard piece of cast iron being
squeezed between a softer flat disk (the wheel) and a flat axle boss. 
This arrangement is not prone to significant warpage due to normal lug
torque imbalances.  It's interesting to note that, in no class of racing
where multi-lug wheel fastenings are used, do pit crews step-torque the
wheels when changing tires.  

In any event, what I was getting at is that you can't automatically
blame all failures on the fact that an impact wrench was used.  It's
necessary to study the mode of failure to determine if overtorque
or uneven torque was a causal factor.