Vertical Flex, Lateral Rigidity - Not Always Right?

[cgates66]

I just built up a new frame, and after riding it around, it got me thinking that maybe this "vertical flex, lateral rigidity" concept is - like a whole lot of pseudo-science in cycling - another overstated, or or maybe mis-specified, issue.

I used to ride a Cannonade SystemSix, with the huge tubes. A great sprinting bike, and super-rigid in every dimension. Handling was a bit twitchy for me, but I loved it right up until galvanic corrosion started to appear, and without that would still be riding it.

I replaced the frame with an Evo HiMod, which was a revelation for out-of-the-saddle climbing. Definitely dances up the hills. Vertically, the Evo's rear triangle has a lot of compliance built into it, so it was also more comfortable and it handled somewhat better than the SystemSix. Sprinting, though, was a bit of a question. It didn't feel as quick as the System, but I couldn't think why as it climbed so well out of the saddle. It seemed to wind up a little bit, but I never felt like I got the benefit of the unwind.

This frame I just built is a fairly rigid titanium frame. And climbing out of the saddle, I'm right back to the SystemSix - which was just fine until I knew what was possible - but surprisingly the sprinting is better than the Evo, immediately obvious, and the handling is better yet again. In the saddle, I'm not persuaded that there's much difference among frames. But this frame has a rigid rear triangle, with some lateral flex in the frame overall.

Anyway, it occurs to me that "vertical flex" might not always be desirable, and "lateral rigidity" might result in some compromises, too. For motorcycles, they try to make the frames laterally soft, and vertically rigid - granted they have suspension...but it makes me wonder.

Is the Evo so great going up because the vertical compliance lets it "bounce" - which is a desirable sensation and probably helps it go faster? But is there a tradeoff: vertical compliance also maybe hurts a sprint, because you wind the frame up considerably under real power and don't get the rebound in phase with your pedal stroke? And likewise, does lateral rigidity perhaps harm handling somewhat by making the bike a little skittish?

I'm 215# so way heavy for a cyclist, which influences my perception.

But I wonder...maybe vertical rigidity has a place in cycling after all. And maybe some lateral flex does also.

It's a curious topic, because I bought the Ti more or less for the exotic / cool factor - it's heavier (although with discs), and I didn't really expect a perception of a performance benefit anyway. Really I wanted to smash in 28c tires, but the Evo...no way. But there it is. Seems to sprint better, and the only thing I can think is the vertical rigidity.