Originally Posted by
samkl
Well, looks like this is going to be more complicated than I thought.
I was going to convert the FSA Gossamer triple crank to a 50/34 double. But turns out no one makes a 34 tooth chainring with a 74 BCD! So now I'm stumped. Maybe I'll have to do a 48/32, or I don't know what. It's really not straightforward, a tandem drivetrain...
Me again. Just ran some numbers through a gear calculator. What range cassette were you thinking? No normal cassette is going to make either of your choices workable. It's really hard to find a cassette that doesn't start with 11 teeth. 50x11 = 122 gear inches. You won't use that a whole lot. Next down is 50x13 = 103". That one you will use. You've wasted a gear and you don't really have any to spare. The low end is just as limited. 34x 34 is 28 gear inches and that is ok (kind of) for a 1/2 bike, but a tandem needs to do much better. 20", 18" even. Let's look at the 48/32 --- 48x11 = 117" That isn't bad actually. I'll just cut to the chase: if you can stomach the cost, a 48/32 x 11-50 12sp makes for about the only 2x system I would send a tandem out into the real world with.