BIKE FIT: Case Study
*Stop, watch the video and think about it before we give you the answer… .
This gentleman presented with low back pain, only on his mountain bike, only on long ascents.
He measures out with an 83 cm inseam which should put him on a 44 to 45.5 cm frame (measured via our method). His frame has a dropped top tube and measures 55 cm.
He has a knee bend angle of 20 degrees at bottom dead center. Knee is centered well over pedal axis.
His stem falls far in front of his line of sight with respect to his hub. Stem is a 100 mm stem with a 6 degree rise.
There is a 2” drop from the seat to the top of the handlebars.
He has an anatomically short Left leg (tibial)
Here is some additional video of him with a 3 mm lift in the left shoe. Look at the tissue folds at the waist and amount of reach with each leg during the downstroke in this one as well as the last. no changes were made to the seat height, fore/aft position of seat. or handlebars.
The frame, though he is a big dude (6’+), is too big and his stem is too long. He is stretched out too far over the top tube, causing him to have an even more rounded back (and less access to his glutes; glutes should rule the downstroke and abs the upstroke). This gets worse when he pushes back (on his seat) and settles in for a long uphill. Now throw in a leg length discrepancy and asymmetrical biomechanics.
- smaller frame (not going to happen)
- lower seat 5-7mm
- shorter stem (60-75mm) with greater than 15 degree rise
- lift in Left shoe
We ARE the Gait Guys, and we do bikes too!