Re: [ST] Suspension question (was: Ride Report...sort of...(long))

["Garry Simmons" <garrysimmons@xxxxxxxxxxxx>]

>If the springs are designed to carry the weight of bike and rider, what
> effect does  damping have on the story?



Damping controls (slows down) the spring movement. Without damping every 
bump would create a series of up and down movements. Compression damping 
slows the movement while the spring is compressing and rebound damping slows 
the spring as it returns to it's normal length. The problem is that the 
unsprung weight of the wheel has inertial once it starts moving, and it 
doesn't want to stop, so the spring over-compresses and then when the spring 
expands again, that unsprung weight of the wheel wants to expand the spring 
more than needed. Damping is there to stop the spring from over-compressing 
and over-rebounding due the inertia of unsprung weight. Which is part of the 
reason people install ultra-light rims and stuff. Ultra light wheels also 
reduce the gyroscopic effect of keeping the bike upright, so it's easier to 
flick the bike from side to side.

Damping is basically shoving oil through a hole. The faster you try to shove 
it or the thicker the oil, the more energy it takes. Kind of like pushing a 
thick liquid out a syringe. The compression and rebound damping adjustments 
essentially control the size of the hole. How that's actually accomplished 
in the fork and shock internals varies, but that's the concept.

If you have too much compression damping, the fork/shock will essentially 
hydro-lock under very fast movements, like hitting a sharp edged bump. When 
that happens, the suspension stops moving and the bike/you move instead. 
That's the getting launched out of your seat feeling. Some high-end 
suspension offers adjustments for both high-speed and low-speed compression 
damping. Too little compression means the suspension will move more, 
possibly bottoming out sooner than desired. Too little rebound damping gives 
a feeling of the bike pogo'ing because the wheel is rebounding too quickly. 
Too much rebound damping and wheel doesn't return to the asphalt as well 
after the bump.

A least that's my take on it. I'm certainly no expert but am trying to learn 
as much as I can since good suspension is worth more to me than horsepower. 
Once you get damping dialed in for your riding style and roads you usually 
don't mess with it much  unless you're going to a track day or something. 
But it's nice to have the adjustment options. Unfortunately, most people 
don't take advantage of them which is why that feature is easily dropped on 
bikes that aren't race-reps. I really, really wish the Sprint had fully 
adjustable suspension.

All that said, getting the proper spring rate for your weight, setting the 
sag and perhaps changing the fork oil weight can go a very long way to 
making a bike handle well and that doesn't cost a ton of money.

Garry

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