I had a issue come up during a bike fit last week and I'm looking for some advice on how to resolve it in the future, or not? Seat Fore/Aft is an area of bike fitting that has been the center of debate. Depending on what you read, varying answers are presented. Knowingly, I ask the question anyhow in the hopes of getting some opinions from other bike fitters.
Typical procedure would have a bike fitter set the shoe/cleats/wedges, and then move up the body to set the knee angle and KOPS. I had a client that seemed to have abnormally short thighs relative to his lower leg. At least this is my guess to what was happening. The knee(s) were set at about 30 degrees of flexion. I then moved the seat all the way forward (while maintaining the knee angle along the way by raising the seat) with a non-setback seat post and still had the knee about 1 1/2" behind the pedal spindle (procedure was per the BFS Manual). The bike was a 2005 Lemond Tete De Course, nothing unusual accept the typical long top tube on a Lemond, seemed to fit him very well except for this seat fore/aft concern. I left him in this seat position because once we set the reach to the handlebars he was reporting good comfort, good balance of contact points, and his pedaling looked very economical without hip rock. Would you have done anything different/more, and why if yes?
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I would say that as long as he is not positioned in front of the spindle he will be fine! If he is feeling comfortable and does not have any hip-rock and knee tracks well, this sounds like a sound and solid fit. Did you try a seat-post with minimal set-back?
ReplyDeleteDid his KOPS improve as you moved him forward? I have found a good percentage of people will continue to self-select their previous position by pushing back on the saddle once it is re-positioned. 1.5 inches is pretty far back.
ReplyDeleteAfter posting my comment above I had a similar issue (the same day, kind of Twilight Zone). My client was a short stature female with VERY short tibiae, and VERY long (in proportion) femurs. No matter what we did her knee was significantly in front of the pedal spindle. She also has a short torso, so there isn't much that can be done in terms of pushing her back, because then her reach is too far (on an 80mm stem).
ReplyDeleteApplicable to seat fore/aft, see link below. I think Paul mentioned this in class. KOPS not always the goal, but a reference. Contact points/pressure and goals of fit matter most: http://www.peterwhitecycles.com/fitting.htm
ReplyDeleteLemonds not only have long top tubes, but also relaxed seat tube angles, which can make it difficult to get KOPS for certain body types(if that is indeed the desired outcome).
ReplyDeleteA possible solution to narrow or even close the 1.5" gap is to try a tri style seatpost, such as Profile Design's Fast Forward. This is obviously a not the best solution, and will certainly change the reach to the bars. Different saddles can also be a solution, as some have rails which will allow you to position the rider farther forward.
Based on the information you supplied, a change in frames is probably the best long term solution. Sometimes folks just don't "fit" their bikes, no matter what we do.
great post
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