There's a range of up-down movement in an mtb that we're interested in here: there's the comparatively slow movement of bike + rider compressing and rebounding-- what you get in a parking lot bounce test-- and then the much faster modes of vibration from trail chatter.
The first (slow) kind is what we tune for when setting spring rate. We can suck up really slow impacts to some extent with arms and legs. The suspension helps there, but starts to really shine at sucking up slightly faster hits we can't react quickly enough to with our muscles.
But as the impacts get faster still, the suspension starts not being able to suck up all the energy-- what with mass, stiction, and damping speed limits, it just can't respond fast enough and so the really fast trail chatter can make it to your body nearly unfiltered by the suspension. At that point the soft parts of your body act like an elastomer and start to suck up the sharp spikes, acting like both spring and damper for the energy. The bones act like shock linkages, sprung by things like ligaments and tendons, but also damped by same, as well as by fluids/blood vessels, plus nerves, muscle, and fat.
Mostly your body is pretty good at that, but over time and with high intensity exposure, it starts to accumulate some damage that can last beyond the ride recovery period. A peculiarity is that it's the smaller, lighter bits that do the most absorbing-- their vibration modes are higher frequency than the bigger bits-- so things like tiny blood-filled capillaries and fine nerves stand to take comparatively greater damage. That's what we see in folks that run poorly damped power toys like chainsaws a lot.
That's where tires, wheels, grips, shoe soles, and indeed Buttercups have a role, and that's why your weight doesn't really matter much.
Feb. 10, 2024, 11:44 a.m. - Flagrant_Mechanic
There's a range of up-down movement in an mtb that we're interested in here: there's the comparatively slow movement of bike + rider compressing and rebounding-- what you get in a parking lot bounce test-- and then the much faster modes of vibration from trail chatter. The first (slow) kind is what we tune for when setting spring rate. We can suck up really slow impacts to some extent with arms and legs. The suspension helps there, but starts to really shine at sucking up slightly faster hits we can't react quickly enough to with our muscles. But as the impacts get faster still, the suspension starts not being able to suck up all the energy-- what with mass, stiction, and damping speed limits, it just can't respond fast enough and so the really fast trail chatter can make it to your body nearly unfiltered by the suspension. At that point the soft parts of your body act like an elastomer and start to suck up the sharp spikes, acting like both spring and damper for the energy. The bones act like shock linkages, sprung by things like ligaments and tendons, but also damped by same, as well as by fluids/blood vessels, plus nerves, muscle, and fat. Mostly your body is pretty good at that, but over time and with high intensity exposure, it starts to accumulate some damage that can last beyond the ride recovery period. A peculiarity is that it's the smaller, lighter bits that do the most absorbing-- their vibration modes are higher frequency than the bigger bits-- so things like tiny blood-filled capillaries and fine nerves stand to take comparatively greater damage. That's what we see in folks that run poorly damped power toys like chainsaws a lot. That's where tires, wheels, grips, shoe soles, and indeed Buttercups have a role, and that's why your weight doesn't really matter much.