dual vs single chain drive

[lyndonw]

I am wondering about the relative efficiencies of two different chain drive configurations for a three wheel recumbant style bike. The bike is pedal powered.

Currently a sprocket at the front drives a single chain that runs to the rear wheel. The chain runs "underneath" another idler sprocket so that the chain can run underneath the rider. The return chain is necessarily very slack.

The alternative which would be more convenient for the overall bike design is the have two seperate chains, one running from the pedal sprocket at the front to an intermediate axle which in turn drives the rear axle. Separating the drive like this would allow the chain to run underneath the rider a little more elegantly and simplify the bike design.

Is there any major efficiency losses in the second configuration compared to the first?

Thanks for any responses

 

[GregLocock]

Yes, I'd expect the second system to give about twice the losses of the first one. Well, OK not quite that bad. Assuming you have a derailleur/tensioner at the rear wheel that is where most of the losses will occur, and the sprockets tend to be smaller as well, which will increase losses.

As in so much else with bicycles, not much is published, you'll probably be better off measuring it.





Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[MikeHalloran]

I'd expect the major efficiency loss >in service< to occur with the second scheme, just because the arrangement makes it less convenient to oil the secondary chain.






Mike Halloran
Pembroke Pines, FL, USA

 

[Philrock]

I agree with GregLocock that the losses in the second system will be higher, but I would add that chains are pretty efficient, and that even if your losses go up 70%, you might not notice, unless you are racing or doing a lot of hill climbing.

The long slack span you now have sounds like a possible maintenance issue and failure (chain derailing) point.

In the interest of keeping losses down in the second scheme, try to keep the sprockets on the intermediate shaft as large as possible; 20 teeth minimum, 30 even better. This is to minimize chordal action, which is a major contributor to chain drive losses.