's Forum Archives - General

Archive Home >> General(1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 )

Upper/lower leg lengths and seat position(3 posts)

Upper/lower leg lengths and seat positionBergMann
Apr 14, 2003 12:58 PM
Does anyone out there (C-40?) have a good rule of thumb for how femur vs. lower leg length affects your KOPS position?

Although I am happy with my general position on the bike, I am trying to iron out some persistent (if intermittent) knee pain issues.

Using John Cobb's measuring techniques, I measured my femur at 46 cm (hip joint to knee joint) and my lower leg at 52 cm (knee joint to floor), and I wear a 46 shoe. Only problem is, Cobb's website doesn't have any advice on how to set up an effective conventional (non-aero) seat/knee position.

Any advice?
The old standard...C-40
Apr 14, 2003 1:35 PM
is to adjust the saddle to place the front of the knee directly above the pedal spindle with the crankarm horizontal. From there, moving the saddle further back seems to promote more torque and lower cadence for a given amount of power and vice versa.

Saddle height is also important. A saddle set too high will lower cadence. As a rough guide, you should be able to drop your heel 2-3cm below horizontal with the crank at the bottom of the stroke. This will insure that you have a reasonable amount of bend in the leg with the foot horizontal at the bottom of the stroke.

Can't help with the knee pain. Too many possibilities, including physical injury, arthritis, etc. Many knee pains are not position related.

Another important factor is gear selection. If you mash big gears that require high levels of torque rather than a high cadence, your knees may always hurt.

Check out for some of the traditional fitting techniques. Personally, I think that most body measurements are too inaccurate to be of much value. I would never spec out a frame based on body measurements. Any real bike with known geometry is the best place to start the fitting process.
Some dataKerry
Apr 14, 2003 5:27 PM
From Bernard Hinault's article in VeloNews (January, 1988!). The average thigh/lower leg ratio is 1.11 in men, 1.14 in women. Coppi was 1.18, Merckx 1.16, Hinault 1.2. Moser was 1.10. In this case, thigh length is knee caps to the wall when seated with the thighs horizontal. Lower leg is top of knee cap to floor while seated as above. There is no precise method of setup, as there are too many personal comfort and flexibility variables. Get a starting position, make small changes, ride for 100+ miles, and keep going in that direction if things seem better. Dialing in a position is a multi-year effort. You could be getting pain for all kinds of reasons beyond your fore/aft saddle position.