[s-cars] RE: More on audi wheel bolts/studs/torque

[Bernard Littau]

Some observations and food-for-thought questions:

Torque for a car's wheels is set by the manufacturer based upon:
the type of metal and width/depth in the hub
the type of metal and the diameter and thread type and pitch of the lug
bolts
the contact area of the lug to the wheel
the type of metal and finish of the wheel and lug.
No A/S or lube on the threads or contact area of lug to wheel, and the
surfaces being clean and intact.
All parts cold.
[I am sure there are other factors, too]

This yields one number, appropriate, very likely, for the average use of the
vehicle in terms of speed, cornering, braking, typical hub temperature and
whatnot else -- with an adequate safety margin thrown in, of course.

Most of this discussion is focused on cars that are not used within these
parameters.

[How many of you use the stock tire inflation pressure while on the track or
pro-rally?  Who even uses the stock tires and rims at any of these sorts of
events?]

Now throw in the switch from lug bolts to studs.  What torque is being used
in this case and why?  What kind of metal are the studs and nuts now?  What
is the diameter and pitch now?  Depth of the threaded part of the nut?

Now torque while hot, what torque do you use while hot -- more or less than
stock or cold?  Why?

If your lugs/hub or studs/nuts are not holding, why is this?  Temperature
cycling, too low of torque, too high of torque (beyond the elastic limit
will loosen, right?), not enough contact area friction, or another reason I
can't even fathom?

Finally, what is correct for one application is not necessarily correct for
another.  In the case of an owner that never pushes their car, and typically
has the wheels removed only when the tires are replaced, some A/S to help
out in the case of a flat by the side of the road might be correct.  On a
track car, this might not be correct, as it throws off the contact area
friction part of the equation as it is perturbed by the heat and stress :-)

Until we get some more specifics, no one has any idea of what we are truly
debating.  Personally, castellated nuts and a cotter pin seem like a good
idea here :-)

Best,

Bernard Littau
Woodinville, WA
'88 5ktq