Changing gearing -- front vs rear

Architeuthis dux rg-sv650 at v0.net
Mon Jun 23 12:19:26 PDT 2008


Kabara, Richard M. wrote:
> Jim, I believe there are two different phenomenon at work here. One is
> contact wear from specific teeth repeatedly touching, the other is chain
> "hopping" due to low number of C/S sprocket teeth...

Chain/sprocket numerology is a hotly debated topic on one of my other 
lists.. I'm a skeptic, but lets run some numbers...

F:14  = 2                 * 7
R:44  = 2 * 2                 * 11
C:108 = 2 * 2 * 3 * 3 * 3

Same F/C every 7 * 2 * 3 * 3 * 3 = 378
Same R/C every 11 * 3 * 3 = 297
Same F/R/C every 7 * 2 * 11 * 2 * 3 * 3 * 3 = 8316

##

F:15  =         3         * 5
R:45  =         3 * 3     * 5
C:108 = 2 * 2 * 3 * 3 * 3

Same F+C every 5 * 2 * 2 * 3 * 3 = 180
Same R+C every 5 * 2 * 2 * 3 = 60
Same F+R+C every 2 * 2 * 3 * 3 * 5 = 2700

##

F:15  =         3         * 5
R:44  = 2 * 2                 * 11
C:108 = 2 * 2 * 3 * 3 * 3

Same F+C every 5 * 2 * 2 * 3 * 3 = 180
Same R+C every 11 * 3 * 3 * 3 = 297
Same F+R+C every 3 * 5 * 2 * 2 * 11 * 2 * 2 * 3 * 3 * 3 = 71280

I thought the resonance might be due to quickly hitting the same pattern 
over and over.

I'm not sure what gear the 41mph was, but I picked a fairly arbitrary 
5000rpm and factored in the gear ratios for 4th gear.  Jim's 14:44 
combination takes well over a minute to cycle back to the same pattern, 
so I can't imagine resonance from this effect.  Even the lousy 15:45 
combo takes many seconds to cycle back.  (The best permutation for wear 
among these is theoretically the 15:44 with a 108-link chain, although I 
think other factors like maintenance and cleanliness would almost always 
outweigh this numerology silliness unless you were to pick some sort of 
really pathologically terrible combination.)

Jim, what was the approximate frequency of your resonance?  And what 
gear were you in?

-rg




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