Hi everybody,

I am a mechanical engineering student who has had an interest in bike fitting now for a couple years. While I am not an actual bike fitting professional, I have spent some time and thoughts on the subject.
I have made a power point presentation which I have attached and would like to hear as much input on it as possible.
To summarize it: If you look at the biomechanical force and momentum equilibrium of the rider/bike system, the derived formula shows saddle setback as a factor affecting the weight distribution on the hands. It also shows that road bike fit is power output dependent (more exact vertical pedal force) and you can not fit A position on a road bike but rather A RANGE of positions the rider will adapt to during different riding scenarios. I also put in some thoughts on the affect of climbing. I myself consider that part not final and think there are other effects at play in this situation too. I included that part to show that I do not think this contradicts my earlier theory.
I have done some experiments with three riders, which showed results represented by the pictures I took of the one rider.

As I said, I would love to hear the input and criticism of some professional fitters on that topic.
Oh and please note that English is not my native language, so I apologize for any grammar and spelling mistakes, and if something should not be clear, I'll try and rephrase it.

And a merrry Christmas to you all,

Ingmar

Your theory is interesting, but very academic. You are assessing hip angle to power output with two variables... saddle for/aft with torso unsupported. This study is a good start. I recommend adding another variable "seat height" to fore/aft torso unsupported. Then add another variable seat angle to seat height to for/aft torso unsupported. Then add another variable cleat position to seat angle, seat height, for/aft, torso unsupported... and so the process goes on. Then look at road and aero bars with these variables. Then start looking at the athlete regarding... ROM, core stability, muscle asymmetries, pelvic malalignment, etc. You will be on your way to becoming a bike fitter. But if you are working towards a mechanical engineering degree you can easily make more money than most fitters:)
Last edited by: gcombs: Feb 7, 13 4:50
I have some thoughts on seat height and all the other metrics, most of it is taken from already existing fit protocols since I am very happy with the methods they supply. I mostly had a disagreement with saddle setback in the fit protocols ive seen or read about. I do not believe that saddle setback (or seat angle) has much to do with power production, muscle recruitment etc. als long as the angles within the body stay the same. (Studies on recumberent bicycles vs. upright cycling in Bicycling Science by Gordon Willson comes to my mind). I think that KOPS might be a statistical result of it and a starting point but not a rule thats set in stone.

Oh and since I am going into the direction of sports( bicycle) engineering, I think bike fitting goes very well along with it.
If you feel that muscle recruitment and saddle setback aren't terribly related, then where do you place core strength within the equation? If we slide the saddle back enough to allow the rider's core strength to support the upper body, then the arms and shoulders are not recruited as much. Many of us place the saddle in a position where the rider can support himself without touching the bars. Arms/shoulders are more relaxed which means more power available for the legs. An individual's core strength should be accounted for somewhere.

Just my two cents.
You have some good points.
I am sorry I guess I put that wrong. Of course, if your arms arent supposed to support the weight from the upper body, the back muscles (most notibly the erector spinae) will have too. And pushing the saddle back a lot will put more strain on the back which 1: the athlete will need to adapt to (build core strength) and 2. will recruit the back muscles that now will need the "power" which therefore wont be available for the legs.
What I meant is that I believe saddle setback mostly influences which upper body muscles are used and the upper body position but not so much which leg muscles are used or how much power you can produce.
In short:
If you want a lower upper body position strengthen your back and move your seat backwards (in contrast to TT fit=> that was the main point of the whole thing)
Well.......I'm going to go with:
- If you have tricep pain, decrease the reach (either saddle fwd a hair or shorter stem) because you're too stretched out and the triceps are fatiguing.
--- Hand/wrist/elbow pain can mean slide the saddle back because there is too much weight on them.

- Sliding a saddle back closes off the hip torso relationship and makes it more difficult to achieve a lower front end on any bike (in most cases).
Reach is definately a thing to consider when there is discomfort in the shoulders hand and arm.

Quote:
- Sliding a saddle back closes off the hip torso relationship and makes it more difficult to achieve a lower front end on any bike (in most cases).

Well here is where i disagree to an extend. I do not believe the hip angle is the only limiter on handlebar drop. I think that most of the time with road bikes the limiter is too much weight of the hand this is the problem with a too far forward saddle position. I think that as long as critical hip angle is not reached even during higher power outputs, the way to achieve more drop is to move the saddle backwards. Which I think the pictures I took with the athlete show.
This I think is the biggest difference between road and tri bike fit. On a time trial bike you can tolerate much more weight on the front, since it is supported skeletaly which allows the trick of "rotating the rider around the bottom bracket" to achieve more drop.
All I ask is where is the anchor the rider pushes from?
Every action has an equal and opposite reaction. If the rider pushes down then his body is pushed up. The anchor is dependent on the position. If the rider is positioned to push straight down then his weight and arms are his anchor. He can easily out push his weight so his entire body is used through his hands, arms, torso, core, to anchor him to the bike. If he is positioned aft, he can use the saddle as more of an anchor, ala Greg Lemond style pushing forward then down, from his book The Complete Book of Cycling. The rider uses less energy to anchor and is able to apply more to the pedal. More thigh muscle is used making for quicker recovery from harder efforts.

http://www.mybicyclefit.com
As a fellow mechanical engineer (now full time bike fitter), I just wanted to say that I am happy to see more and more people actually think about these things and questioning the old and useless rules of thumb. Keep up the good work.

Jonathan Blyer,
ACME Bicycle Co., Brooklyn, NY
Thank you, I really appreciate it, especially from someone who really knows that stuff. My aim is to work with bicycles after I graduate and I believe it is a good idea to have some basic knowledge of all the important parts of the sport.