Ted as usual is 100% correct, "Twiddling" as we use to call it,thats what counts.I have NEVER had ANY problems with my knees.even after all these 60+?years of riding. On the bike trail in Parker Co. I?DID ride with a chap that ALWAYS pushed a REAL big gear, 56x11 most of the time, to see him ride was like watching SLOW MOTION, 40-50RPMs tops,of course going 25-35MPH. WELL, did NOT see him for a few weeks, then he was running on the trail! I asked "Whats the problem Dave" "John my KNEES gave out, Dr says NO more cycling for a while" THIS IS A TRUE STORY!? KEEP THE BLOODY REVS UP UP! look after the knees,?use the BIG gears for downhill. NOW of course there are exceptions, IF you have a big enough engine and are racing to beat the clock, THEN the big gears can help. I am reading a real good book from England, Roy Greens "100 years of Cycling Road Records", In 1951 I did a 25TT in 58+ mins, Twiddling my arse off! well D.C Lloyd in 1982 in Brit land did a 25 in 42-37!? 16+mins faster than my time,.?his average speed 35.197MPH?PUSHING a 62x13 top gear on a six speed block! Lloyd also did in 1974 a 50Mile in 1hr 35 45! Wonder what he trained on!?Is he still riding? I know the 40k(25miles) times are in the low 40s now a days. BUT for the average rider, TWIDDLE. think of the future. A cane or walker is no fun in later life. Cheers John Crump OldspinemBrit, Parker. Co USA