The adjusters only alter "low speed" damping as they move a tapered needle in and out of a valve, but this is only for slow movements, when the suspension is hit harder the oil flows past shims (shim stacks) changing the oil weight will affect both high and low speed damping, also on many bikes the adjusters make relativey little difference, I have had bikes where there is no discernible difference with 3-4 clicks on adjusters and a minimal difference between min and max settings.
I think ti be entirely correct the adjusters alter or "trim" the damping curve, but if you look at graphs from a shock dyno you will see the adjuters have a pronounced effect on the damping at low speed, and a neglible difference at high speed.
By High Speed and Low Speed I mean the speed at which the forks / shock is moving up / down, not how fast your going.
On my Wilburs shock I have High and Low Speed compression adjustment for compression damping, Wilburs say slow speed damping affects up to 20" per second, and high speed from 20" up to 15ft per second and I would guess the faster the movement the less affect the adjuster would be having, whereas different oil would affect the entire range in a more linear fashion.
http://motorcycleinfo.calsci.com/Suspension.html
20 miles per hours is about 30 feet per second, but I am unsure of matey's maths as the bike will partly lift over the bump, and the spring / damping / bike weight (sprung and unsprung) will all change how much the bike lifts compared to the suspension moves - I think his maths are for "perfect" absorbtion of the bump (i.e. bike sits dead level and you do not feel the bump as you go over it) but the article is interesting and explains how suspension works very well for basic "street bikes" but I think it is quite old as most shocks are now gas charged on all but the cheapest bikes.
This article is better for modern shocks and shows how shim stacks work, and how the adjusters affect the damping curve, if you look to the left of the diagram on the first page you xan see open "clickers" Vs closed "clickers" (these are your adjusters) make huge difference, but by the end of the curve make little difference (and remember from article one the shock dyno goes nowhere near as fast as shock do in the real world, so this is probably more like low-mid speed damping as opposed to true high speed damping)
http://www.shimrestackor.com/
I think ti be entirely correct the adjusters alter or "trim" the damping curve, but if you look at graphs from a shock dyno you will see the adjuters have a pronounced effect on the damping at low speed, and a neglible difference at high speed.
By High Speed and Low Speed I mean the speed at which the forks / shock is moving up / down, not how fast your going.
On my Wilburs shock I have High and Low Speed compression adjustment for compression damping, Wilburs say slow speed damping affects up to 20" per second, and high speed from 20" up to 15ft per second and I would guess the faster the movement the less affect the adjuster would be having, whereas different oil would affect the entire range in a more linear fashion.
From here:-
http://motorcycleinfo.calsci.com/Suspension.html
20 miles per hours is about 30 feet per second, but I am unsure of matey's maths as the bike will partly lift over the bump, and the spring / damping / bike weight (sprung and unsprung) will all change how much the bike lifts compared to the suspension moves - I think his maths are for "perfect" absorbtion of the bump (i.e. bike sits dead level and you do not feel the bump as you go over it) but the article is interesting and explains how suspension works very well for basic "street bikes" but I think it is quite old as most shocks are now gas charged on all but the cheapest bikes.
This article is better for modern shocks and shows how shim stacks work, and how the adjusters affect the damping curve, if you look to the left of the diagram on the first page you xan see open "clickers" Vs closed "clickers" (these are your adjusters) make huge difference, but by the end of the curve make little difference (and remember from article one the shock dyno goes nowhere near as fast as shock do in the real world, so this is probably more like low-mid speed damping as opposed to true high speed damping)
http://www.shimrestackor.com/
