I'll agree that this and Kelvin's explanation seem to cover the subject.
Some times when you get too close to a problem the answer eludes you. (I
can't the Forrest all these damn trees are in the way)
>From a practical point of view it would seem that the natural tendency of a
knock off to tighten would reach a limit and no further driving would cause
it to get any tighter. If you could exceed this natural self tightening
limit with a BFH, then it would seem to hold that no further tightening would
occur while driving. This does not solve the problem of Knock offs coming
loose when moving in reverse as breaking torque is not the same as tightening
torque.
So I'm happy, I have an explanation that my feeble mind can get around, and I
thank you all for your efforts.
One thing though, if a lug nut is less than finger tight don't sweat the lug
nut coming off, the threads on the stud are stress risers and the studs will
break long before the lugs come off. (Ask me how I know this)
Rick Ewald
67 MGB with very tight Knock offs (but I won't tow backward)
In a message dated 4/21/99 10:42:37 PM SA Eastern Standard Time,
mvheim@studiolimage.com writes:
> I thought a further word would help clarify the difference in the
> situations, beyond Kelvin's impressive explanation. It boils down to
> this: the center lock nut on the wire wheel is at the center of rotation
> of the wheel; the five (or four) individual lug nuts are not. Therefore
> the lug nuts do not experience any actual rotational friction between
> them and the wheel (that is, rotation on the center of the threads) --
> they experience (if anything) linear friction (across the center of the
> threads, therefore not contributing to loosening or tightening), if the
> wheel shifts on the studs under braking/acceleration. Presumably what the
> Chrysler (and other) engineers were worried about was angular momentum
> loosening lug nuts that were *already* loose (less than finger tight), to
> the point they would fall off.
>
> In other words, the rotation of the wheel itself acts directly on the
> knock-off, rotating it in the direction of either tightening (forward) or
> loosening (reverse). The rotation of the wheel does not act directly on
> the lug nuts, since no lug nut is at the center of rotation. The lug nuts
> experience angular momentum and centrifugal force, but not rotation on
> the center of the threads. This is why modern motor manufacturers are
> satisfied with non-handed lug nut threads, and no one warns about towing
> steel wheel vehicles backwards.
>
> BTW I have no special knowledge of this and am just reasoning from first
> principles, so if you have a better explanation, fire away...
>
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