iliveonnitro said:
Kerry is advocating 1.08 or 1.10*inseam height, whereas the Guimard is .882*inseam. This is a big difference. For me, the difference between these two formulae is a 72.9cm saddle height and 90.8cm saddle height. Uh, 18cm difference? Either of you care to clarify?
Whoever posted saying that saddle fore-aft doesn't affect power: I completely disagree. Try moving your saddle back .5" (and seat height lower to compensate) and do a 2 minute interval. Now move it back to original and forward .5" (seat higher to compensate) and do a 2 min interval. Which has more power? I guarantee the forward position will.
During hard efforts, do you notice that you (and pros) wind up sliding forward on the seat? This is, to a lesser degree, similar to standing. This can affect many things, but a big one (mentally referencing Bicycling Science, 3rd edition, MIT Press) is that moving forward in the saddle puts your position more directly over the bottom bracket. This translates to more power to the pedals. It also increases the tendency to mash. In the long run, there is back pain, too.
Many bike fitters get saddle fore-aft wrong. When using a plumb line, you should not measure from the top of the knee. If you straighten your leg and pinch the patella on each side of the knee--that should be the reference point. This is another reason why most people slide too far forward on their saddle during normal riding conditions...improper fitting.
um, the difference is that one measurement is to the center of the bottom bracket, and the other is to the pedal spindle.
as for fore-aft, there is this law of conservation of energy, see, and when you stand to get on top of the pedals, yes, you can move your weight so that your weight can be used to push down on top of the pedals, so that your muscles aren't being flexed to do it quite as much through that range of the pedal stroke. But it's the same amount of power, overall, because you have to lift your weight.
the idea that a few mm or even a cm of fore-aft can discernibly influence the power you develop is really kind of absurd, when you think about it, particularly for the reason you cite. You slide around on the saddle way more than that couple of mm. Yeah, when you are "on the rivet," you are forward. It's a natural thing. But I think it has more to do with leg extension than anything else. as you madly turn the pedals and your form goes to sh*t, you creep forward. I'm not sure exactly why you creep foreward, truly, but you don't, I believe, get more power out of the deal. It's about shortening the reach more than getting more weight on top of the pedals. You already have plenty of weight over the top of the pedals. If your bottom isn't moving up and down with the pedals, the weight is doing no work. That's elementary physics.
as for the measuring from the patella or wherever thing -- come on. what does that anatomical feature have to do with ANYTHING? anything at all?
