28 to 39 gap too big?

[madencbm]

Tandem with campy: 53-39-30, 12-30 cassette. Want some lower gears and not sure how well the campy long cage derr. will handle 12-32 cassette. Also the IRC campy compatible to get 32 tooth is very expensive. So.. what about replacing 30 with 28. Will there be any problems with front derr. shifting or anything else?

[Ralph]

The gap from 28 to 39 not too much, but currently the shift to 39 is maximized for it to come from a 30, not a 28. Some say it won't matter much, but my experience with trying to shift rings not matched to each other is you will notice the difference. Or use a TA for middle ring if you have issues....it's not designed to be matched to another ring....but has pins to aid shifting.

Other issue is maybe the chain will be too slack to use the 28 with the smallest cogs....which I'm sure you don't do anyway. You could take out 2 links, but then maybe big to big won't shift.....and break RD, if case you forget. Other thing to check out....and you can do this before you make change...eye ball this..........will the chain rub on the bottom of FD cage if small ring smaller. I imagine a rear cassette with a 32 would work out fine with a real long cage.....not a med cage...which some call long cage.

I have a friend with a tandem currently running a 26-39-50 on front with long cage in rear and 12-30. Works great. They are limited somewhat on their top pedaling speed.....but after about 35 or so....he just coasts LOL.

[oldpotatoe]

Originally Posted by madencbm

Tandem with campy: 53-39-30, 12-30 cassette. Want some lower gears and not sure how well the campy long cage derr. will handle 12-32 cassette. Also the IRC campy compatible to get 32 tooth is very expensive. So.. what about replacing 30 with 28. Will there be any problems with front derr. shifting or anything else?

Put many 28s and even 26t onto Campag and other, triples. Just reduce pedal pressure when shifting to it...maybe a chain watcher.

[FlashUNC]

Don't see much point if you're just going down by two teeth on the front, especially at that low of a chainring size anyways. Is sub 1:1 in the rear necessary for the tandem?

[ColonelJLloyd]

Back in the day many (most?) tandems had half-step plus granny setups so the jump was often 45t to 30t or 28t. With friction shifting it works great with most FDs.

My 1979 Jack Taylor came with this setup. Can't remember exactly, but I think it's 50-45-26.

Untitled by ColonelJLloyd, on Flickr

[madencbm]

Thanks guys for the advice. On a single 28 maybe not be necessary but tandem on third day of tour with hard climbing we want every bit help we can get!

[madencbm]

Followup question. All 28t 74 bcd chainrings I can find are 9 speed or called 9/10 speed compatible. Will there be problems with my 10 speed chain? Not sure what 9/10 speed means if size of teeth or spacing between chainrings are different.

[ColonelJLloyd]

10s chain will be fine.

[Billybob62]

Originally Posted by ColonelJLloyd

10s chain will be fine.

+1 - Also agree that the jump is no problem. I've used 28 rings to replace the 30 on Campy 52-42-30 cranks with no trouble at all (but agree that a chain watcher won't hurt).

[Bostic]

Originally Posted by FlashUNC

Don't see much point if you're just going down by two teeth on the front, especially at that low of a chainring size anyways. Is sub 1:1 in the rear necessary for the tandem?

Yes. Dalewood Way, the SF version of Marin in Berkeley. We use a 30x32 on our Tandem.

[Bradford]

I'm running two bikes with jumps down to 26 and they work fine. I do use a chain catcher though, which I would recommend.