Originally Posted by DaveSSS

You're mistaken about the front/rear weight distribution of a 481 compared to the newer 565 or 585 frames. The chainstay length, is the same. How you get your butt back a specific amount behind the center of the BB does not matter. It can be done with STA or seatpost setback and the weight balance will be the same, unless some other part of the the geometry is different. In this case, what is slightly different is the front-center of these two models. The 381/481 in the 51cm size that I owned is 571mm, compared to 580mm for the 51cm 565/585. The shorter front center of the 481 would increase the amount of weight on the front, but only about .6%. A .6% difference won't make or break the climbing or descending ability of a bike. I've made saddle fore/aft changes that create much larger weight shifts than that and never had a problem climbing or descending. I do 10 mile mountain climbs several times a week and the same length of technical descents, with lots of curves. I also own a KG461 with an in-between 575mm F-C and I've never noticed any significant difference is climbing or descending ability with any of them.

The new 585 optimum frame has a shorter F-C of 573mm. The problem I have with it is the head tube is too tall. Even with the shortest headset top, the head tube would be 150mm in length. I use a 145mm length with a 73 degree stem to produce a 12cm drop to the bars.

Another thing that changes the front/rear weight balance significantly is torso angle. A rider in an upright positon will have less weight on the front than one with a low torso angle. I really can't imagine pedaling seated on climbs so steep that the front end gets light, but I tend to lower my toroso on hard steep climbs or get out of the saddle, so perhaps that is the difference. I never use the top of the bars with an upright torso on a steep climb. I have my hands on the hoods, my arms bent, with a low torso angle, much the same as I would use for aerodynamics on the flats. I feel that I can apply more torque to the crank in this position, compared to riding more upright.

FWIW, I tried a 51cm R3 a couple of years ago when they were a hot item. In the 51cm size, the F-C is an incredibly short 558mm that creates a lot of toe overlap. The steerer trail is MUCH smaller than a LOOK, which makes for some quick steering when combined with the incredibly short wheelbase. I rode mine for 200 miles, tore it down and sold it on E-bay. Didn't like it at all. Bought a 585 the next week and I've been happy since then.