rhm

Hey Binky,

First of all, I don't know anything about your MS bike.

As to the cranks... Biopace rings have been out of fashion for many years now, and though there is a bit of a resurgence of poplurity now, they are still widely loathed. I, personally, like them; but that is neither nere nor there. At any rate the difference is very subtle indeed. My guess is they are more likely to be good for your knees than bad; but what do I know. When researching them your first order of business has to be to separate the logic behind them from Shimano's marketing; always try to determine the writer's prejudice.

I would also advise you to do some reading on crank arm length; some people recommend shorter crank arms for those with knee injuries. Again, determine the writer's prejudice before you make any conclusions: I, for example, am a big proponent of short crank arms for every rider, so you'll find many posts in which I advocate them, but I don't know the specifics of your case and I'm not a doctor anyway. That said, your old MTB probably has 175 mm crank arms, which are appropriate for serious off-road riding but are not necessary for riding on smooth flat surfaces. If you're going someplace where you're likely to get bogged down in sand or mud, you may want them; but on fire roads etc. you would be better off with shorter crank arms.

At any rate, I suggest you take the question of crank arm length seriously. With shorter crank arms your knee joint doesn't open or close quite as far, so if the problem in your knee is at one of the extremes, then shorter arms might help a lot -- but consult your doctor. Oh, and... by shorter crank arms I mean much shorter crank arms. 5 mm makes very little difference. You may be able to get something as much as 35 mm shorter than what you have now, which would make a noticable difference.