Good Suspension Setup

Originally Posted by Sid Squid

Wrong.

Under any given load the spring compresses the same amount, changing the preload changes only your position in the suspension's travel.

It's a dynamic system, the spring is not reduced in length under load by preload changes.

The force needed to compress a spring increases as the spring is compressed. So it is stiffer when compressed relative to when it is uncompressed. If the preload adjustment compresses the spring by a fixed amount then surely the effective spring is stiffer than when uncompressed.

Or maybe it's all in my mind. Wouldn't be the first time I have been mistaken - that I can admit to.

Originally Posted by ejohnh

The force needed to compress a spring increases as the spring is compressed. So it is stiffer when compressed relative to when it is uncompressed. If the preload adjustment compresses the spring by a fixed amount then surely the effective spring is stiffer than when uncompressed.

Or maybe it's all in my mind. Wouldn't be the first time I have been mistaken - that I can admit to.

Edzakary

[northwind]

Um, no offence but that'a pretty horrible guide there... Lots of bike-specific assumptions, but more importantly it contradicts itself constantly- it tells you to use preload to set sag, but also that it's to be used for stiffness- then, when addressing too soft/too hard issues, addresses only damping and doesn't mention preload. It's not all bad but there's too much simplification, some actual out and out mistakes, and plenty of room for confusion. Lots of better guides out there. Ohlins, WP, Traxxion among others will agree with Sid Squid here, but you're absolutely right, you can find people stating it either way quite easily.

Originally Posted by northwind

Um, no offence but that'a pretty horrible guide there... Lots of bike-specific assumptions, but more importantly it contradicts itself constantly- it tells you to use preload to set sag, but also that it's to be used for stiffness- then, when addressing too soft/too hard issues, addresses only damping and doesn't mention preload. It's not all bad but there's too much simplification, some actual out and out mistakes, and plenty of room for confusion. Lots of better guides out there. Ohlins, WP, Traxxion among others will agree with Sid Squid here, but you're absolutely right, you can find people stating it either way quite easily.

Yeh I just did a quick search for this. I was mainly pointing out what preload does to a compression spring in general

Originally Posted by ejohnh

The force needed to compress a spring increases as the spring is compressed. So it is stiffer when compressed relative to when it is uncompressed. If the preload adjustment compresses the spring by a fixed amount then surely the effective spring is stiffer than when uncompressed.

Or maybe it's all in my mind. Wouldn't be the first time I have been mistaken - that I can admit to.

Well in fact I do have to admit that I was wrong in referring to 'stiffness' which is in fact a constant when relating to a spring. It's a measure of the force required to compress it a unit distance apparently.

Having admitted that I will insist that my rear suspension is now 'firmer' than it was before because It compresses less from its current preloaded position than it did before. So there is much less lolloping about going through bends.

Originally Posted by ejohnh

Having admitted that I will insist that my rear suspension is now 'firmer' than it was before because It compresses less from its current preloaded position than it did before. So there is much less lolloping about going through bends.

changing preload does have some secondary effects:

- changes rear ride height
- changes rear suspension geometry - which changes the rising-rate ratios & hence *may* make the suspension stiffer
- some other things I've forgotten

by increasing the preload you will be storing energy in the spring by compressing it, ie the spring wants to decompress so is applying a greater force between dogbone and frame, that effect makes it feel stiffer.

Originally Posted by injury_ian

...

nope, sorry, but that's not right

stiffness = spring rate [1]

people think that the rear end is "stiffer" because it compresses less, but this is beacuse the extra preload causes the suspension to sit higher in its stroke, not because the spring rate has changed (it hasn't)

if you go nuts with the preload you can cause the suspension to bottom-out on the compression, or top-out on the rebound, which again can be erroneously thought to be making the rear "stiffer" because you''ll either effectively have *no* suspension on bottom-out, or get kicked out of the seat on top-out


[1] all other things being equal - ie damping, etc.

Haha, now I have no idea what's going on. I've tried to get my head round the basics of suspension, preload, sag, rebound, compression damping etc. etc. Too many terms!! Now I'm even more confused

But it has got me hunting round the forums for old info so I can finally try to twiddle with my setup and see how it goes before I consider the 'popular' front spring and oil change.

Originally Posted by MeridiaNx

Haha, now I have no idea what's going on. I've tried to get my head round the basics of suspension, preload, sag, rebound, compression damping etc. etc. Too many terms!! Now I'm even more confused

But it has got me hunting round the forums for old info so I can finally try to twiddle with my setup and see how it goes before I consider the 'popular' front spring and oil change.

Yep, I have had a gutsful of this too. Bottom line is that if you up the preload you decrease the amount the spring will compress for any given load - so it 'feels' like the spring is stiffer - honestly Sid, I know that in absolute terms the spring will always retain its stiffness coefficient.. I just wish I could say the same for the other thing