Originally Posted by
Carbonfiberboy
I found an 11-40 9-speed cassette on Amazon for our tandem. Works fine, but one needs to add a Wolf Tooth Roadlink to move the RD down.
The knees are a perpetual geezer issue, though some folks hit geezer at 40. Oddly enough, the cure is to do unweighted full depth squats, hams on calves, first slowly working up to going down that far, perhaps over a period of many months, doing a few squats say every other day. Always stop at the point where discomfort begins, never pushing into pain. Then after one can get all the way down, doing like 3 sets a couple times a week. If you've ever visited the Middle to Far East, you'd see people resting in that full squat position on street corners. It's very comfortable and human knee joints are built particularly to be able to do that resting position.
That said, you really are better off with the shorter cranks, regardless of knee issues because your legs will spend more time with less knee bend, which is the stronger range of motion.
I was stationed in South East Asia during the war and I do remember the seated position you are describing. Just thinking about that makes my knees hurt. When I got out of the service I went to work with my father as an apprentice plumber. The older guys that worked for my father would tell me not to kneel on the concrete. At least use a piece of corrugated cardboard they would say, but I was 24 years old and I knew everything. I should have listened but as my uncle used to say, "Smart too late". Thanks again for your help and I will give the exercises you described a try, carefully.
Be safe.
P/s: What was the brand 11-40 cassette you found? Might be something I will need in the future.