rdtompki

I'm looking for information on drive train efficiency as a function of chainring and cog size. I'm considering buying a Davinci tandem which has an extra transfer chain and very small chainrings (plus, of course, a timing chain). Probably won't make much of a difference in my decision, but the engineer in me wants to know.

Mr. Underbridge

I'm tempted to think that the differences will be negligible compared to more significant factors such as air and rolling resistance. Particularly since we're talking a tandem, it's not like you've reduced yourself to counting grams.

Even if it has double the drivetrain loss of a normal bike, that should still fall below the noise threshold of aerodynamic drag. Just a guess, though.

If you decide to let your engineer self take over, then I see a motor and a powertap in your future.

rdtompki

You're right about the powertap. The geek in me is really interested, but I'm too old to worry much about "power" output. On the tandem a powertap would only result in my yelling at my stoker (wife!). Come to think of it that's one of the tremendous advantages of a Davinci. I could coast and measure the output of my better half; I can see the finger pointing now!

tcs

See the article beginning of page 14 of:

https://www.ihpva.org/HParchive/PDF/hp51-2001.pdf

and the article beginning on page 3 of:

https://www.ihpva.org/HParchive/PDF/hp52-2001.pdf

HTH,
tcs

meb

We also had a couple of technical threads going further with the data of the above cited article back in the fall of 2003 over at rec.bicycles.tech, but I currently unable to find it.

meb

Actually it's the Spicer article this article cites that is on point to your question:
https://scitation.aip.org/getabs/serv...cvips&gifs=yes