Originally Posted by
pbass
I have a Surly Cross Check that I'm always messing with, changing bars--flats, drops, "alt" type bars w backsweep. It works a number of ways, it's a WIP. These bikes are known for their long top tube and short head tube and can be tricky to fit for some. I actually went down a frame size on mine from the first one I had. One phenomenon that seems really counter-intuitive is that when I extend my reach w different bars, I feel like I'm putting less weight on my hands. I suppose it's because I'm engaging my core more because I simply have to. The opposite is true with the alt flat bars w significant backsweep---they're fun and put me in a more upright, theoretically comfy position, but I end up kinda scrunched and leaning on my hands. This does not seem to be the case though with my other bike, where it's more what I'd expect - shorter reach, less weight on hands. Looking at the two bikes side-by-side, and measuring things, they're actually really close the way I've got them set up. Just something about the Cross Check frame....it's weird...
Your are correct. It is counter-intuitive. It's all about torque. When one leans forward on a bike, one's center of gravity moves forward of the saddle, creating a torque about the saddle. One can support the torso by using one's core muscles, but what's really happening is that one is creating a counter-torque using the pedals and saddle. If you took your feet out of the pedals, you'd fall forward. But supporting the upper body with only core muscles gets tiring. We prefer also to use our arms to support our upper body, thus creating another counter-torque. Torque is force X distance. The greater the distance, the lower the force necessary to create the same torque.
Note that I'm assuming we are trying to resist a constant torque. If in moving one's hands forward, one also leans more forward, or scoots more forward on the saddle, the force on the hands is not lessened by moving them forward. Thus first we get well balanced on the bike using saddle position at our comfortable hip angle and then select stem length for comfort. I suggest that the difference between the two bikes is saddle position w/r to the forward pedal, cranks horizontal, or possibly hip angle.