Nick Payne
Joined: 10 Jan 2004
Posts: 2625
Location: Canberra, Australia8/23/13 11:08 PM |
Goniometer and saddle height
I've always been rather unscientific when it comes to setting saddle height. When I first got interested in cycling in the 1970s, the method I used was to look up a friend who was quite a good pro cyclist. I rode over to his house, and he stood on the footpath and watched me ride by. "Your saddle's too low", he said, so we raised it 1/4" and I rode past again. Two or three iterations of this and he said "Try that for a while". So I did. And every time I got a new bike, I would put the saddle up or down in small increments until it felt the same height as on the previous machine.
However . . . when I came across an article on bikeradar which covered four different methods of setting saddle height, I read it with some interest:
http://www.bikeradar.com/fitness/article/how-to-get-your-seat-height-right-14608/
The most interesting method seemed to be the final one, using a goniometer to measure the angle of the knee at the bottom of the pedal stroke. as it wouldn't be fooled by things such as differences in sole thickness or cleat stack height or long femur/short tibia vs short femur/long tibia. I thought "Well, I don't have a goniometer, but I have a digital camera that can shoot slow motion video, and Gimp has a measuring tool that measures angles, and I should be able to achieve the same result by measuring off a frame of video taken at the bottom of the pedal stroke".
And it was pretty easy to do. I set the bike on the trainer and camera at the side on a tripod. I put three small fluorescent stick-on paper circles each side on my leg, one over the greater trochanter (the bony protrusion at the top of your femur), one over the lateral malleolus (the bony protrusion on the outside of your ankle), and one over the axis of the knee joint (the point that seems to remain at the center of both the upper and lower leg as the knee bends). I shot 20-30 seconds of pedalling from each side. Loaded the videos to my PC and opened them in vlc, played them back at ultra-slow speed, froze the playback at the bottom of the pedal stroke on each side, and used the facility in vlc to take a snapshot of the frame. Loaded the snapshots into Gimp and used the measure tool to measure the angle between a line between the dot on the knee and the lateral malleolus, and a line between the dot on the knee and the greater trochanter.
Luckily my measurements came to between 25 and 26 degrees each side, which according to the article was pretty much in the ballpark, so I won't have to change my saddle height :-)
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