HandsomeRyan

I know there must be some reason that tandems use such large chainrings for the timing chain (or belt), I just don't know what it is? I guess maybe the traditional standard BDC spiders allow for swapping out chainrings without some expensive proprietary system but wouldn't using smaller cogs (around 18 teeth) allow for a slight weight reduction, higher ground clearance, and a shorter chain?

Does anyone here know why tandems use [relatively] large chainrings on the timing chain side?

Retro Grouch 

Reduces tension on the timing chain and extends the life of the timing sprockets?

TandemGeek

Pretty much, but this is a worthwhile read: https://www.sheldonbrown.com/synchain.html#chainring

Charles Ramsey

Cog life and chain life is the cube of the difference between the cogs. 40 teeth timing chains and cogs will last 8 times as long as 20 teeth timing chains.

508Jaguar

I thought it was because they had less carbs. ;-)

Or was it MORE carbs..... I can't remember these things.

rdtompki

It's a good thing I never use my 12-11 combination, my drive train would explode in nanoseconds

chichi

Handsomeryan thats an interesting rack on the front of your single speed, who makes it?

zonatandem

Back in the '70s we used 28T timing chain rings on our Assenmacher. Worked fine.
Currently using 38T on our Zona.

Dean V

Our old Bob Jackson has 32T timing chain rings and they have lasted for a long time. As for the extra chain tension loading the frame etc, maybe in theory, but I haven't noticed any detrimental effect and the BJ is a very flexi steel 531 frame.

HandsomeRyan

[off topic] I welded it up myself. I posted a thread about it here. It works really well to do only one thing- transport 6 bottles of your favorite glass-bottled beverage. It's as much a styling element as a real "utility" accessory but I've been pretty happy with it. In the summer I plan to make a different, more CETMA-esque, flat rack for that bike and maybe put the six-pack rack on a different bike. Rigth now I take the bottles out and throw my heavy chain and lock in the carboard six pack holder while I ride.



[/off topic]

merlinextraligh

At least in theory, smaller rings are going to be less efficient as well. And it would not take much efficiency loss to quickly trump the small weight advantage.

Besides, Gates doesn't make a belt to fit with smaller rings.