Originally Posted by Joe Minton (Post 16812306)

I am 72. My wife is 63. Neither of us have been cycling long. I am overweight by 40# (it was 50# a month ago). Our granny gearing is 24 front and 32 rear for 21 gear inches. When we do an eight mile ride around where we live, we can expect to climb a total of 1300+ feet. It is "up" in any direction we choose to go. Some of the hills feel pretty steep to us and, I am sure, others.

There are times when I am glad for the 21" gearing. My wife needs even lower if I expect her to keep riding, with me or at all. I'll install an 11-36 cassette on her bike and shall have to also change the RD. It'll cost over $100 to do so but is certainly worth that cost.

Both our Cannondales (SL1 & Synapse) came with triple (30/39/50) front & 12-28 (10 speed) rear. The lowest gearing was 28-inches. Both now have 24/39/50 and 11-32; the lowest gearing is now 21-inches. A 33% reduction. Nancy would not now be riding if I had not made this gearing change. I am getting and shall continue to get stronger; a medical condition may not allow that for her.

My strong advice is to install whatever gearing you need to ride and climb comfortably. By comfortably I mean: do not use such a 'tall' gear that you hurt yourself climbing and such that you dread even getting on your bike. This is supposed to be fun and, in this, case -- don't listen to anyone who tries to give you an upper limit on what size cassette sprocket you may use or a lower one on how small the front granny can be. It may cost some to get it right for your situation but it is your situation and no one has a right to put a limit on what you do to make riding fun.

Joe

Originally Posted by MileHighMark (Post 16802922)

A 9s Shimano MTB rear derailleur will work with your 10s 105 shifters. The MTB derailleur will handle cogs up to 36t. I have this setup (34/50, 11-36) on my commuter, and it works really well.