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1936 Bugatti Atlantic Replica Project
Knock-Off Hubs Discussion

We know that for many decades the Dunlop/Rudge British wire wheels have utilized opposite hand threads on their center lock hubs; RH threads on the left side, and LH threads on the right side. The Dayton installation instructions emphatically specify the same set-up, warning that the wheels can come loose if the adpters are installed on the wrong side, or if the car is towed backwards. So where does the "self-tightening" (or at least "anti-self-loosening") torque come from?

These pages:

shed some light on the phenomenon of epicyclic fretting precession as the dynamic involved. However, they both attribute the precession to the contact of the hub adapter and the K.O. cap tapers. This explanation works for the Rudge stye hubs, but leads to a self-loosening result with Dayton style hubs, where the K.O. cap taper fits inside the hub.

I submit that the epicyclic fretting precession at work here is predominantly at the contact of the threads of the hub adapter and K.O. cap. (illustrations below) This analysis then works to support "self-tightening" of both Rudge and Dayton style K.O. caps.

This Wikipedia page on precession (mechanical) reminds us that bicycle pedals are left-threaded on the left-hand crank so that precession tightens the pedal rather than loosening it. The pedal's threaded stub is smaller than the female threads in the crank, so forward pedalling rotation precesses the pedal threads even faster counterclockwise, tightening left-handed threads. (This is an inversion of our case here.)

Disclaimer: I'm not a racer or an authority on knock-off hubs. I'd like to hear from you if you can offer a more definitive analysis on this subject. Bob at:


Here's an illustration of the epicyclic fretting precession principle:

epicyclic fretting precession

Analysis assuming the K.O. cap threads fretting contact is the source of epicyclic precession; Rudge, then Dayton:
thread precession - Rudge thread precession - Dayton

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