I put this in frame building, because it seems to me that frame builders have excellent motivation to understand the ins and outs of frame geometry.
Conventional wisdom seems to be that short chain-stays make a bike a better climbing bike. I read this all the time, but I never see any discussion as to WHY that is so.
I can see two possible reasons:
-Stiffness: Short members flex less under high chain tension, keeping the rear wheel (and hence the whole bike) running on a straight line, and absorb less energy in the tubing itself.
-Balance: Short chain-stays put more weight on the rear wheel, and prevent wheel spin in low gears.
In particular, I'd like to know if this same wisdom applies to very large frames....64cm and up. If this is something "you can just feel" then it may well apply to more "normal" sized frames, and less so as the frame is scaled up....if most riders ride normal sized frames, then most riders might agree on something that doesn't apply to not-normal sized frames.
I'm fairly tall (6'5") but extremely long of limb. I've never been able (or willing, I guess...I am Scots!) to shell out the dosh for a custom frame. The factory 27" frames (no, not the wheel size...think 67cm frame) of the late 70's and early 80's fit me pretty well, and I enjoy riding them when I'm not truing or replacing the rear wheel. These frames typically scaled up all tubes _except_ the chain-stays. The result is that the rider's tail-bone ends up over the rear axle, or nearly so This shifts much more of the riders weight to the rear wheel, and tall riders are also heavy....It has been a long time since I weighed 190# and I was damned skinny at that weight. Pumping newspapers up and down a hilly route through my teens has given me huge legs that are not balanced by a heavy upper body...so my weight is in my legs, and the front wheel carries little weight.
Pretty much the same thing happens when I run the seat post out 8" on my modern 64 cm frame....modern wheels are a bit better(rims are lots better, but increased gear count causes too much dish) so I've had fewer issues. Running a tandem spec wheel is a possibility, but I still think my bike would handle better with a better weight distribution, and a tandem wheel seems like a case of treating the symptom rather than the underlying problem.
I've also been a bit leery of having a custom frame that is off the beaten path built. As I explain above, it seems like big companies with lots of resources don't quite get it right. I can judge a builder's craftsmanship by samples of their work, but their wisdom and insight with regards to dimensioning a frame for a tall rider is trickier. Leonard Zinn may well understand the ins and outs of a tall frame, but he is justifiably proud of his work (and prices it accordingly) , and as for others, who knows? I'm sure some would build whatever I spec....If it doesn't work out, I've got a frame that is too big for 95% of the potential market where I might unload it, and probably not well suited for those who can ride it. My finances are such that it would be a real stretch, and I'd only have one shot in my lifetime to get it right.
I'm finally about to the point where I'm ready to try my hand at frame building, and I'm thinking I want to build myself a tall frame with ALL the tubes scaled up. The cost of the parts, and my time, I could risk. I could try a geometry (or three) with modestly priced tubes and rattle can paint, ride it a while, and build another with the fancy tubing, lugs, and Imron when (if !) I get it right.
If the goal of short chain-stays is to put a "normal" rider's weight back, then this should be a non issue, as the F/R weight distribution should be maintained. If the concern is stiffness, then beefier stays should address that. Oh yes, and if I run panniers on it, then the longer chain-stays help clear my size 14 (Eu 50) heels that are turning 180mm cranks.
Any help understanding the trade-offs one makes with regard to chain-stay length will be appreciated.