I have a basic understanding of suspension and wanted some clarification regarding preload. My thinking is that springs are progressive. Therefore the more you compress them the stiffer they become. So the lighter the rider the less preload is needed to obtain the correct sag. The heavier the rider the more preload is needed so that the spring is compressed more before the weight of the rider is added. When the rider then sits on the bike the spring compresses less under the heavier weight as the spring is now within a stiffer section of its compression. If anyone understands what I rambling on about, please could you comment on my thoughts.
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it is far more simple than that
springs can be of a progressive type but.
increasing preload merely lengthens the suspension and increase the height of the bike so that when the rider sits on the bike the bike is sat at the optimum ride height remembering that ride height also effects geometry.
progressive springs aren't slowly progressive throughout their length they are usually made with two rates soft being the first part of the spring used this gives comfort and stability then when compressed either by braking or cornering the harder part comes into play.
It's important to understand what you're doing while cranking down on that adjuster. Increasing preload does not result in a stiffer spring. It only changes the amount of load it takes to begin to compress the spring. Spring stiffness is determined by the manufacturing process, and is usually expressed in lbs/in or kg/cm. As an example, a 100-lb/in. spring preloaded 2 inches will not compress further with any weight less than 200 pounds, but will compress 1 inch per 100 pounds above that. Normally, stock springs should work well enough unless you are very light or very heavy, or if you carry gear or ride two-up. If you find that you are near the limits of your preload adjustments to achieve proper static sag, you may need to consider changing your springs.
How to set static sag can be found here..... And that is where you really want to start....
so if im currently only getting around 5mm static sag and a further 10mm sag when i sit on the bike do i need to add preload (shorten the spring length) or take it off (increase spring length). as i thought the spring would become stiffer the more it was compressed/ preloaded and therefore reducing preload would give me more sag for my weight.
Reducing the pre load will give you more sag.
Confusion over terminology?
I'd call that 5mm of free sag and 15mm of static sag.
Anyway, it isn't very
much sag so maybe there's a bit too much preload. Was it set up for
two up riding or a man-mountain, and how does it compare with the front?
much stiction is there, in other words how much can you vary the
measurement by slowly allowing the suspension to settle from being pressed down
(with the help of a friend), or lifted (by putting your feet down)?
the effects of any rising rate linkage, reducing the preload will have
no effect on the working length of the spring, it will simply reduce the
ride height for a given weight.
However, if the suspension is
completely unloaded, e.g. on a centre stand or an Abba stand, then reduced
preload does mean allowing the spring to extend slightly. Making sense?