CYCLINGFORUM.COM - Where Cyclists Talk Tech --- Return To Home

 

    Register FAQ'sSearchProfileLog In / Log Out

 

****

cyclingforum.com ****

HOMECLUBS | SPONSORS | FEATURESPHOTO GALLERYTTF DONORS | SHOP FOR GEAR

Return to CyclingForum Home Page CYCLING TECH TALK FORUM
          View posts since last visit

Goniometer and saddle height
 

Author Thread Post new topic Reply to topic
Nick Payne
Joined: 10 Jan 2004
Posts: 2625
Location: Canberra, Australia

8/23/13 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 :-)

 Reply to topic    

Sparky
Joined: 08 Dec 2003
Posts: 19068
Location: PDX

8/23/13 11:44 PM

We made a Goniometer out of a 1/4" sheet of ply with a hole for the knee position and arced slots for the hip and ankle with degrees marked. I did this after riding the Scott with the seatmast as part of the frame which I do not want to cut as I want to sell it and not rule out taller folks than I as buyers. Thus I wanted to know two things. How high a saddle adjustment would open the extension too much, and how high I should try to get back to after being mostly recovered from the femoral nerve damage. I had raised all my bars and lowed all my saddle so I could actually ride.
I hated this position on the bike and not riding with my hips rotated forward as I have been for years.

I determined with the DIY gauge the the saddle on the scott without cutting the frame/seatmast was 1/2" higher at best [lowest rail/top stack seat] than the max I should attempt. I knew it was too high when a 10 mile ride had my lower back unhappy.
This is when I found that link and made the DIY Goniometer.

I am now about 1-3/4" higher than the lowest during femoral radiating pain riding. Which is higher than I used to ride by 3/4" and doing a bit less heels down than I ever have and doing well with it at the upper range of extension of the knee. 26-8^ best my DIY gauge indicates.

 Reply to topic     Send e-mail


Return to CyclingForum Home Page CYCLING TECH TALK FORUM
           View New Threads Since My Last Visit VIEW THREADS SINCE MY LAST VISIT
           Start a New Thread

 Display posts from previous:   


  
Last Thread | Next Thread  >  

  
  

 


If you enjoy this site, please consider pledging your support

cyclingforum.com - where cyclists talk tech
Cycling TTF Rides Throughout The World

Cyclingforum is powered by SYNCRONICITY.NET in Denver, Colorado -

Powered by phpBB: Copyright 2006 phpBB Group | Custom phpCF Template by Syncronicity