reohn2 wrote:and so do frames that are designed differently to fit a person of a given size.
Outside of bespoke frames does that really count for most people....
Well, yes it does; rather obviously for frames intended for different purposes, and often rather less obviously for frames that are intended for similar purposes.
For example, loaded touring can cruelly expose differences in stiffness of otherwise similar-looking framesets; one may shake it's head like a startled whitebait, and another won't move even half as much. Other times you can use the same gear setup on two frames and one will rub the front mech like fury and the other one won't.
In terms of raw comfort once you have 35mm + tyres then maybe half or two thirds of the 'comfort' comes from the tyres. [If you have tyres that fat enough maybe the frame stiffness doesn't matter, (comfort wise).] But with skinnier tyres that proportion decreases and in any event it is not insignificant in most cases. A good portion of the remainder comes from the frame and fork.
Years ago I 'straightened' a gaspipe frame and fork (that had been in a head-on ding) use brute force technology. I decided (in a fairly simple-minded fashion) to try simply reversing the forces that had bent both fork and frame. I built a 'thing' that allowed me to bear one end of a scissor jack onto the BB and the other end onto a dummy hub mounted in the end of the forks. I quickly found that (between the flex in the fork and the frame) the fork tips would spring over an inch (maybe an inch and a half) before they would take a new 'set'. It actually kind of worked, too; I had a bike that I could at least experiment with, even if I didn't fancy passing it on to anyone.
However it was clear that both the frame and the fork were flexing and contributing to the movement. [Subsequent ad-hoc experiments using heavy gauge tubes as levers, inserted into the head tube and the seat tube of steel frames, amply demonstrated just how springy the main tubes of a frame can be.]
This means (in crude terms, for steel) that you can most likely have a very good fatigue life even if the fork routinely moves about 1/3rd as much (as is required to give a new 'set') as you ride down the road. A frameset that maximises its contribution to comfort can be seen working in exactly this way as you ride down the road, and one that is perhaps stiffer/stronger won't move anything like as much. In the simplest possible terms, if it is built to take a hefty chap and a touring load, it won't move so much when a slightly built rider uses it unladen.
I think that a lot of bike frames are somewhat overbuilt these days. If I were making and selling bikes to all and sundry, I'd probably build them this way too. And if I wanted to occasionally load a given machine up to the gunnels, I'd buy one that was overbuilt and put up with the reduction in ride quality when unladen.
But if I otherwise have a choice, I'll ride a bike that is built just so for the conditions of use; like a cup of tea made just the way you like it, you know when it is right!
Re 'Pete's machine'; that is interesting, I'm almost lost for words...
cheers
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