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karavshin 10-30-08 05:56 AM

Physiological Fit and Handling Fit
Many fitting systems I've read about target a physiologically-optimal frame geometry spec for a few different bike styles (mtb, road, tri, tt, etc). The idea being it gives you either/and most efficient possible power delivery or the least-damaging for joint/muscle.

Then when I am reading about designing a frame, it discusses geometry in terms of how the bike handles as a function of frame geometry (trail, wheelbase, etc).

The issue will be that the physiologically ideal point (it seems like most of these fitting systems produce a single optimum point description) isn't going to necessarily going to match your desired bike handling characteristics.

It seems to me that the practical answer I really want is to imagine the physically healthy geometries set and the handling geometries set, and find out where those two sets overlap, and somewhere inside there is the bike geometry(ies) you actually want.

In particular I'm thinking about this for MTB and travel/touring frames, where there are more considerations than just efficiency and speed.

So a couple questions:

1) has anyone seen a fitting system that optimizes for both physiological fit and handling fit?

2) has anyone seen rideable adjustable bikes? Would be nice to actually experience what arbitrary geometries ride like. Or at least allowing some parameters to be adjustable (wheelbase, trail, angles).

NoReg 10-30-08 10:12 PM

You could be looking at this at a higher level than my interest, but I don't see the conflict, except at some pretty small increment of wheel base. You can design your power position around the seat post angle to the BB plane, and you can design your handling around your head tube angle and trail. To get reach right about the only thing you face is a possible change in wheel base from what might be wished, and you can deal with some of that through the stem if you had to.

Road Fan 10-31-08 10:20 AM

I'm not a frame builder or designer, but isn't fore/aft weight distribution one key factor in designing for good handling?

One thing I have done is to adjust my fore-aft position on a few of my bikes to get 55r/45f distribution, and it can result, with my lard-ass, in some funky knee positioning.

From this experience and my more general experience as a design engineer, I would NOT expect that for all riders, there is an overlapping or sweet spot that satisfies both the requirements for efficient/safe fit and the requirements for best weight distribution. The more constraints you add to a design problem the fewer actual solutions (by this I mean solutions that contain minimal compromise) exist.

Road Fan

NoReg 10-31-08 11:41 AM

+1 with enough factors it's always a compromise.

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