[s-cars] Re More on Wheel Torque
QSHIPQ at aol.com
QSHIPQ at aol.com
Thu Oct 24 09:35:54 EDT 2002
[ Picked text/plain from multipart/alternative ]
Looking at it a bit differently, Wolff. If you use A/S on a audi wheel bolt,
and torque to 81 ft/lbs, you have the equivelent of torquing a dry bolt
install to 110 ft/lbs. Kinda puts those A/S use claims in perspective. In
reality, with A/S and audi dry spec all you are claiming is that you are
routinely way overtorquing your wheels. Make sure you routinely ck the
hardware for wear, thread stretching and wheel hole cracking.
WRT porsche Jolly, a couple things to consider with that claim (I'll assume
it's valid). First, *if* it is specified to use lubricant, then they are
giving you a wet torque specification. With an alloy nut (especially), if
you use the wet torque specification on a dry nut, you are *undertorquing*
the wheel by definition. Using anything other than the exact specified
lubricant will over/undertorque that application.
I'm intrigued by a few things researching this intensively. I've seen a
bunch of TSB's regarding "not" using lubricant on bolts/nuts/studs. One of
the truck fleet procedures didn't say anything about lubricant, it only
listed "140lb/ft (dry)". Wonder if that's enough? Audi and other marques
just assume you know what that means. Unless specified otherwise, ALL
torques should be considered as dry torque values.
Another anomoly (scarey) that appears to need clarification. The 2 piece
nuts are considered the best for torquing wheels (hey I have those on my 4
runner), and the specification for most of them is to lubricate the nuts.
Further reading indicates this to be lubricating the 2 pc nut itself, NOT the
threads/land/ or studs.
In a message dated 10/22/02 11:38:01 AM Central Daylight Time,
wolff at turboquattro.com writes:
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
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,
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