Originally Posted by
sapporoguy
Our drive train: 24/39/50 x 12-36 9-speed cassette with 700X35C tires, for about 18 gear inches on our Co-Mo Speedster. Shifting requires a little care, but it got us fully-loaded across America this summer without ever having to walk uphill.
But!
We kept wishing we had just one lower gear, especially through Appalachian climbs we barely made.
Our FSA Gossamer MegaExo cranks have a 130/74mm bcd spider, which won't take lower than a 24T.
Is anyone using a 22T granny gear on your tandem, and how?
-Any tandem crank with a 104/64mm or 110/58bcd spider and the same FSA external-bearing bottom bracket?
-Anyone switch to square-taper BB to get smaller spiders? (I see DaVinci and Middleburn have options with interchangeable spiders, but expensive.)
-Any other solutions you've found to get one lower gear combo? (Bigger big cassette cog, perhaps?)
You can achieve the same result of 22 in front by going with a 40 in back. For example with a SunRace CS-M980 9 Speed 11-40t or similar.
With the 11 in back you will also have more top end. In fact the 39-11 combo matches your current 50-14 combo.
So if you are willing to lose your topmost gear of 50-12, then you can just run the system as 2x9 and remove the 50 ring altogether.
Which is likely going to be required anyway since if you run 11-40 with 3 chainrings you will have exceeded all of the capacity ratings of the derailleur and it may shift horribly.