RobC

Got this from the VFR mailing list. I'm posting this without the author's permission, so I'm including his name as well. Can't vouch for his credibility. Just want to offer another view on a hotly debated topic.

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From: "Rouleau, Joseph S" <joseph.s.rouleau@boeing.com>
To: "'vfr@cs.wisc.edu'" <vfr@cs.wisc.edu>
Subject: lugnuts / torque
Date: Mon, 28 Jan 2002 14:24:12 -0800
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I've read a lot of interesting comments on the lugnut issue. Here's a mechanical engineer's input:


First, understand how a lugnut works. I write this generically, and it applies to any vehicle so equipped. There are many ways to prevent a threaded fastener from backing off, and all critical fasteners must use at least two for safety. The lugnut on an automotive wheel is kept in place by 1) elastically deforming the threads, and 2) the tapered cone. Lugnuts are
typically not designed to accept other lesser forms of retention: chemical (Loctite), interference (Nylock, Helicoil, or other inserts), lockwashers, or safety wiring.


So what happens when you torque your lugnuts? 1) the stud threads are stretched a small amount, well within the elastic range of the metal. If you overtorque it, you will permanently deform the stud and invite cracks, etc. 2) the cone of the lugnut seats in the taper of the rim (just like a Morse taper). Torqued properly, the interfacing surfaces are held in compression and will prevent the nut from loosening. While additional torque will indeed make the cone more effective in retaining the nut, overtorquing puts too much stress in the material and can cause cracks or galling, especially in the lightweight aluminium or magnesium wheels today. The engineers specify a torque value for a reason!!!


That said, let's dispel some myths. The condition of threaded portion of the stud isn't that critical. That is to say, it works fine whether the threads are clean or dirty, greased, loctited, or whatever. Thread stretch isn't significantly affected by the gunk you have on your threads, and lubrication doesn't hurt anything. However, in extreme cases, contamination or lubrication may throw the torque value off. (Applied torque = stud preload + thread friction + cone friction) My recommendation is to keep the threads clean and apply a SMALL amount of antiseize lubricant to the threads to prevent corrosion and to make it easy to get the lugnuts on and off. I wouldn't locktite your threads as it just makes it harder to remove your wheel next time around, but feel free to use it if you want to.


The cone of the lugnut, however, is CRITICAL. This interface, as far as i'm concerned, might as well be considered the primary locking device because it is more effective than the thread preload at preventing nut loosening. Obviously the taper is also what locates the wheel rim properly on the hub, one more reason to keep grit out of there. When installing the lugnut, both the taper and the cone of the nut must be clean, dry, and free of chips, cracks, or defects. DO NOT lubricate this part of the nut. DO NOT add loctite or anything at all. If you wax your rims, DO NOT wax this part of the rim.


Finally, use a hand torque wrench to verify that the torque is correct (80 ft-lbs for the VFR, ~100 or more for most cars). Honda's engineers are competent, so they have built in a safety factor for those people who go over or under by 10% or so (on account of variable thread friction primarily). While some powered (pneumatic/electric) torque wrenches are well calibrated, most are not very accurate, so just double check torque by hand. Since the VFR has only four lugnuts, I can't see any reason for the average motorcyclist to need a powered wrench. Are we that lazy?


Sorry for the long-winded post...


J Rouleau
Seattle, WA

TicketProof

your leaving yourself open on this one ;-)

trebien

So, whatever you do, do NOT wax or lube your tapered cone???