ultrazenith":3bfx6kdm said:So if I've understood correctly, a bike's speed (for a given rider fitness) is primarily down to its ability to smooth out the bumpiness of the trail?
Not necessarily, there is a lot more to it that that. But being able to ride rough stuff with more traction and control (by far), greater grip (even just modern rubber, not necessarily big wheels), far better brakes letting you maintain speed longer into corners and trail features, so on and so forth. You can ride anything on an older bike, but you can't necessarily ride it the same. Things might be close on the climbs, and on featureless flat terrain (paths, fireroads) but when it gets rougher and more tech the same rider on an equivalent modern rig will walk away from themself on a vintage bike.