I have an old mountain bike (15 yrs old or so) with Biopace eliptical sprockets. A friend of mine mentioned the other day that eliptical sprockets can be hell on your knees. After having this bike for most of it's life, I've not had a knee problem, but is this something to consider? I'm in my mid 30's, and don't wanna screw up any major joints...I use it to commute to work (10 miles RT) and to do some extra riding in Central Park occasionaly.
I'd like to get up to riding 15-20 miles per day, 4-5 times a week, if I can.
If I do decide to go with new sprockets, would it just be worth getting a new (and lighter) bike instead of doing an overhaul on a 15 year old bike? I really like it, but would look for a new one if only to cut a few pounds off the weight of it....
Biopace chain rings are easier on the knees then round ones. The problem with them is that they are less efficient at a higher cadence.
In the last year I have owned 3 bikes, in this order: a comfort bike with round rings, an older road bike with biopace, and a road bike with round rings. I live in a hilly area, and the only bike that I could ride without getting any knee discomfort, was the bike with the Biopace rings (and this bike was geared very high compared to the others).
However, feel free to use any excuse necessary to get a new bike.