Originally Posted by
79pmooney
Part of the equation is wheelbase and weight balance between the wheels. Smaller frames often get shorter in front to reduce the reach. If the front wheel comes back, then if you want to keep a proper weight balance between the wheels, yo u need to bring the rear wheel forward, This means reducing the clearance between the tire and the seattube or FD clamp. Solution? Steepen the seattube or bend it. Not a lot of fans of curved seattubes and the bike's gotta sell.
And the seatpost/setback issues? Changing seatposts to a larger setback post is easy. (Well on any bike that doesn't use a proprietary seatpost and tube or mast.)
I have my customs built with steep seattubes (74 and 75) for weight balance and run custom 60mm setback posts with the clamps centered on the rails. Bikes handle great and the ti railed seats love being centered, (Slamming them means breakage at over $100 each time and a lousy ride home. I also make sure the clamp has a "soft" edge, especially at the lower back. Use a file on it if it doesn't)
Ben
For the fore-aft balance thing, I think there might be two things, but I think only one is significant. First is the weight on the front and rear wheels. Going back to the mid-1970s, "Bicycle Frames" by Joe Kossack says (p. 24) that British designers of the day generally tried to get 45% of the bike+rider weight on the front wheel and ... well, the rest on the rear. This is termed as being for good handling. I've never seen anything that says what goes wrong if you don't achieve this.
More significant for me is the location of my body center of gravity (CG) to the BB. When I ride no-handed I need either be planted on the saddle or to have my CG above the BB. If I don't I'll fall forward or backward. When I'm in the drops or deep into the hoods, I don't want too much pressure on my hands and especially if i have to remove my hands to negotiate a bump, scratch an itch, take a drink, or make clothing or anatomical adjustments, I don't want too much sensation of weight pulling me forward. I also like to lift my body, sometimes including my hands, off of the contact points to negotiate bumps (no, I do not know how to bunny hop). That body weight distribution is managed by moving the saddle back relative to the BB, either by sliding the saddle along the rails or getting a seatpost with more setback. Obviously, KOPS is not a significant part of this beyond being a rough philosophy. I near always end up with my knee significantly (1 to 2 cm) behind the pedal spindle.