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

wolff at turboquattro.com wolff at turboquattro.com
Tue Oct 22 09:48:11 EDT 2002

The first reference (DANotes) and the third reference (loctite) basically
agree that the K number of a lubed thread is between .11 and .18 depending
on the lubricant. The first reference lists .30 as the K number for an "as
received, stainless on mild or alloy" thread and .20 as the K number for an
"as received mild or alloy on same" thread .   Loctite says:
T=torque (in-lb, ft-lb, N-m)
K=torque coeficient or nut factor (determined experimentally for their chart
of lubes and specifically not "friction coefficient" which is a different
lower value)
F=clamp load (lb,N)
D=nominal diameter of bolt (in, ft, m)

So if we keep F and D constant while changing K (the type of lube or lack of
lube and thread material), T will vary by as much as 63%.
That's seems like a lot to me. If we use the lower .20 dry thread number and
take an AS K number of  .15 which looks like about an average value in
loctite's chart then either F goes up 25% or you have to cut the torque 25%
to not raise your clamp load. What this tells me is that you can't just lube
your lug bolts and torque them up to 82 ft-lbs or you are exceding the
factory expected clamp load. Also, anytime torque is given for any threaded
fastener, it is critical to note what (or if any) thread lube is specified.
Will I lube and torque my lug bolts to 61 ft-lbs? Absolutely not and neither
should you based on my uneducated ramblings and an unknown real K number for
Audi size and grade lug bolts. Locktite says "In critical applications it is
necessary to determine K values independently."
Throwing more chaff out for the radar,

"Nobody can forget the sound." - Michele Mouton

> Is this of any helP?
>  http://www.mech.uwa.edu.au/DANotes/threads/preload/preload.html
> "..only 10% of the applied torque generates preload..."  followed by
> something about molybdenum-disulphide grease etc.
> say about 1/2 the way down the page.  Or
> http://www.twoguysgarage.com/site/presection.php?PreID=112&SegID=184
> FWIW, Loctite's opinion may be located somewhere in
> http://www.loctite.com/pdf/antiseize.pdf
> in which it seems the discussion perhaps ought to be (per Monica Lewinsky)
> little more specific about what kind of anti-seize you blokes are using on
> your nuts.
> mlp

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