Recently, too recently, I had need to be fitted to my new tri bike. Given the difficulties of doing it myself, I elected to have it done a lcoal bike store. Wrong move. They were TERRIBLE. Absolutely shocking result.
Anyway, I reread just about everything Sloman has ever written, with a view to getting a good fit. With that info and recommendations from other trigeeks, I did eventually get a good bike fit. Just in time for IMNZ this weekend.
Anyway, much of Slowmans recommendations revolve around 90 degree angles (plus or minus small amounts) There doesn't seem to be any real explanation of why 90 degrees works for all these body angles. I THINK I've got it sussed. :-)
TANGENTS! (and perpendicular)
The leg angle relative to the torso needs to be 90 degrees since it is perpendicular to torso and pushes (primarily) against the mass of the torso. Cycling to a large extent is a glorified leg extension (don't go beserk with all the nuances of pedalling "circles") so having the torso perpendicular to the force being applied seems logical.
The upper arm needs to be 90 degrees from the torso because when on the aero bars, the torso is rotating forward around the fulcrum of the pelvis/saddle. The upper arm needs to be tangent to the force being applied by the upper part of the torso. At 90 degrees the torso is suported skeletally without any shear forward or aft, at the elbow pads (assuming the forearm is also at 90 degrees). At less than 90 degree torso/upper arm angle, (too bunched up) the forearm tends to slide off the back of the elbow pads, necessitating a pull forward by the hands and forearm. It also tensions the upper chest, reducing breathing efficiency and increasing ineffective calorie useage. This will slow you down for no reason. Greater than 90 degrees means sliding forward (or at leasst the tendency to do so, resulting in a necessity to push the body back, with the arms, again using energy and tightening the chest, wasting energy that could otherwise be used by muscles (legs and trunk) for actual propuslion.
The lower arm needs to be 90 degrees to the upper arms, primarily so that the lower arm interface with the elbow pad is perpendicular to the force being applied by the torso. ie, so the arm doesn't tend to slide forward or back as explained above.
So what do you think?
One thing I haven't been able to figure out is why the leg shouldn't simply be vertical, the torso still at 90 degrees, with the torso (measured between hip and shoulder) perfectly horizontal, with the upper arms still at 90 degrees (and vertical, similar to the legs. The lower arms would still be at 90 degrees to the upper arms (and horizontal) with the elbow pads below the seat, by an amount equal to the upper arm length.
The only two reasons I can think of are bollocks. As in where do they go in such an extreme (by traditional standards) position? The other one is weight transfer. Rotating the entire body forward transfers a greater amount of weight to the elbows, reducing weight and stability/power at the pelvis. Remember that for the leg extension, the legs need a platform to push against. With less weight at the seat, less power out of the legs? (or a evere bouncing motion which would quickly destroy bollocks mentioned above) Of course in the above extreme horizontal torso position, visibility would suffer horribly but you'd go off the road at much higher speed than normal eh? :-)
Your comments (and not just "TriDork, shut up, you're an idiot"!!) :-)
TriDork
p.s. this is not just flame bait!! Enquiring minds wanna know!
TriDork
"Happiness is a myth. All you can hope for is to get laid once in a while, drunk once in a while and to eat chocolate every day"
Anyway, I reread just about everything Sloman has ever written, with a view to getting a good fit. With that info and recommendations from other trigeeks, I did eventually get a good bike fit. Just in time for IMNZ this weekend.
Anyway, much of Slowmans recommendations revolve around 90 degree angles (plus or minus small amounts) There doesn't seem to be any real explanation of why 90 degrees works for all these body angles. I THINK I've got it sussed. :-)
TANGENTS! (and perpendicular)
The leg angle relative to the torso needs to be 90 degrees since it is perpendicular to torso and pushes (primarily) against the mass of the torso. Cycling to a large extent is a glorified leg extension (don't go beserk with all the nuances of pedalling "circles") so having the torso perpendicular to the force being applied seems logical.
The upper arm needs to be 90 degrees from the torso because when on the aero bars, the torso is rotating forward around the fulcrum of the pelvis/saddle. The upper arm needs to be tangent to the force being applied by the upper part of the torso. At 90 degrees the torso is suported skeletally without any shear forward or aft, at the elbow pads (assuming the forearm is also at 90 degrees). At less than 90 degree torso/upper arm angle, (too bunched up) the forearm tends to slide off the back of the elbow pads, necessitating a pull forward by the hands and forearm. It also tensions the upper chest, reducing breathing efficiency and increasing ineffective calorie useage. This will slow you down for no reason. Greater than 90 degrees means sliding forward (or at leasst the tendency to do so, resulting in a necessity to push the body back, with the arms, again using energy and tightening the chest, wasting energy that could otherwise be used by muscles (legs and trunk) for actual propuslion.
The lower arm needs to be 90 degrees to the upper arms, primarily so that the lower arm interface with the elbow pad is perpendicular to the force being applied by the torso. ie, so the arm doesn't tend to slide forward or back as explained above.
So what do you think?
One thing I haven't been able to figure out is why the leg shouldn't simply be vertical, the torso still at 90 degrees, with the torso (measured between hip and shoulder) perfectly horizontal, with the upper arms still at 90 degrees (and vertical, similar to the legs. The lower arms would still be at 90 degrees to the upper arms (and horizontal) with the elbow pads below the seat, by an amount equal to the upper arm length.
The only two reasons I can think of are bollocks. As in where do they go in such an extreme (by traditional standards) position? The other one is weight transfer. Rotating the entire body forward transfers a greater amount of weight to the elbows, reducing weight and stability/power at the pelvis. Remember that for the leg extension, the legs need a platform to push against. With less weight at the seat, less power out of the legs? (or a evere bouncing motion which would quickly destroy bollocks mentioned above) Of course in the above extreme horizontal torso position, visibility would suffer horribly but you'd go off the road at much higher speed than normal eh? :-)
Your comments (and not just "TriDork, shut up, you're an idiot"!!) :-)
TriDork
p.s. this is not just flame bait!! Enquiring minds wanna know!
TriDork
"Happiness is a myth. All you can hope for is to get laid once in a while, drunk once in a while and to eat chocolate every day"