Chain & Sprocket, Design Question

[R_Mxtp1]

The internet is full of information pertaining to chain and sprocket design, but there's one question that I've never found the answer to. Hopefully, a member here will be able to provide that answer. In this case, the question pertains to the chain drive on a motorcycle, specifically the Ducati 1199. The rear sprocket carrier and carrier flange have been designed to allow the sprocket carrier to move/roll laterally on the carrier flange. Many bikes share a similar design. The question is why? Why should the sprocket carrier be allowed to move laterally? What is occurring with the chain and sprocket during gear changes, throttle changes, etc. that would necessitate such a design. Could the single-sided swingarm configuration of the bike be factor? I can speculate, but can anyone provide a definitive answer?

 

[EdStainless]

It is to compensate for changes in alignment.
Flex in either the frame, trans mounts, or suspension are resulting in enough movement that you need to allow some 'give' in the system.

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P.E. Metallurgy, Plymouth Tube

 

[R_Mxtp1]

The swingarm is attached to the frame at two points with pins, spacers, bearings and seals. I can see that varying road conditions, high speed cornering, etc. may induce swingarm movement and alignment issues, but there just seems to be something more to it. My mind keeps coming back to the chain and sprocket dynamics.

 

[R_Mxtp1]

What about gear changes or abrupt throttle changes? In that instance, the speed of the driving gear changes, the driven gear reacts, the chain wraps more fully around the rear sprocket and runs hard on the upper chain slider shoe... does the chain also want to shift laterally at that moment?. If so, I could see where a sprocket carrier designed to move laterally would accommodate this movement of the chain, reducing wear on the side of the sprocket teeth and chain plates and also reducing the likelihood of component damage or a chain jumping the sprocket.

 

[MikeHalloran]

Under chain tension, the frame will bend some.
Under chain tension and under braking, the single sided swingarm will probably bend more.
Both the driven and driving shafts have some allowable endplay.
And there are tolerances on everything that relates the driven and driving sprocket's locations.
Given all of that, it seems smart to allow the driven sprocket to find its own operating plane.


Mike Halloran
Pembroke Pines, FL, USA

 

[R_Mxtp1]

Thanks... and I assume that the bend that you're referring to would be a bend to the left (for a bike with the sprocket mounted on the left), correct?