English as a second language is tough, you'll get there.
Come on guys - a technical debate is cool and sometimes we even learn something. I did. I'm intrigued by Pete's comments about just how much difference to the handling it makes. I'd like to find out what else is happening there
Letting it descend into personal insults makes it just a pissing contest
Ah shit! Sorry, I forgot. This is K B - no adults allowed
I may not be as good as I once was, but I'm as good once as I always was.
We have a reg customer here, who road races an R6. Was complaining of the handling. It turns up here, with no sag whatsoever, stiff as a board. Back the shock preload off, give it some sag, and viola. Traction and suspension compliance. Because...it's softer. Obviously on big hits, it makes no diff whatsoever, as that's only spring rate as you've pointed out. But my point is, backing off the preload, most def makes the first third (or thereabouts) of the susp softer.
Nice to see the OP has a way through this. DMTD on this forum had a Diavel and rated it as an excellent and very well handling bike.
Genuine question - was that static sag (bike only) or sag with bike plus rider?
I've seen this sort of thing once or twice before. Too much preload and the shock was topping out on the rebound and was wondering if it could be the same thing. Decreasing the preload didn't actually soften the suspension but it felt that way.
I may not be as good as I once was, but I'm as good once as I always was.
My understanding of this is rudimentary to say the least but the spring , unless progressively wound remains a constant?The spring never becomes softer or harder itself.Therefore reducing preload reduces the force needed for a bump to make the spring react and conversely more preload requires more force for the spring to react to a bump. Compression controls softness/ firmness, but looking at what I just wrote it looks like preload and compression would act in tandem to control the level of softness/firmness? Could this reult in somebody with too high a spring rate or too much preload trying to compensate with too little compression or the reverse?
This is the commonest misconception. To increase or decrease the spring reaction, you need to compress it or lengthen it. Preload does neither - it just raises or lowers the swing arm. The spring stays the same length.
Your comments about the spring properties and compression damping look OK though and the comment about the wrong spring rate shows real insight. It's common for people to try and correct for the wrong spring rate by fiddling with the damping, but then its much easier than changing the spring.
I may not be as good as I once was, but I'm as good once as I always was.
I struggle with preload affecting ride height as surely that would affect geometry and could be potentially dangerous? For example, winding in a lot of preload at the rear, steepening the front steering angle and making the bike unstable? Certainly adding or removing preload changes at what point in its stroke the spring will react to a bump.
Go and have a look at your bike - you will see what I am saying almost immediately. Also the point of preload is to get your suspension back where it should be when you add or remove weight - so it's intended to keep your steering head angle the same.
Yes, changing the preload changes the rest position of the shock and so it changes the start position for any movement. Preload gets you back to the same start point when you change the load that the bike is carrying.
To take this a bit further and to expand on your comments on spring rate, when I add the wife to the beemer and select the appropriate electronic suspension setting, it actually applies preload to raise the bike above where it would be with just me on it. This is because it recognises that the spring rate is set for just the rider and so when a pillion is added the spring is not stiff enough. So it arranges for more travel on the compression stroke and changes the damping rates accordingly.
Yes, it's a compromise, but changing the spring when I add a pillion is a bit tricky.
I may not be as good as I once was, but I'm as good once as I always was.
Of course preload compresses the spring - that's the entire point of it. By what mechanism do you propose preload raises and lowers the swing arm?
This is precisely what altering preload does. You compress the spring without changing the length of the shock - it therefore takes more weight to make the bike sag by the same amount. So for the same given weight, more preload means a higher ride height.
At first I said that preload has no effect on softness or hardness of suspension. I thought about it and of course I WAS WRONG.
F=kX is Hook's law this tells you that to first order at least a spring with constant pitch is linear. k is the spring constant and X is the displacement of the spring. The spring constant k can only be changed by cutting or lengthening.
If you apply a force to the spring to move it X distance it should be obvious that at that distance the spring has a restoring force that is equal. If you preload the spring, which is a change of X you will have a restoring force of kX. The spring constant is k and is constant for this kind of spring, and is referred to as stiffness, this is important because the term stiffness can be misinterpreted. The upshot is that preloading a spring means that you have to overcome the restoring force in order to compress the spring, which in turn means it's going to take more force to start the spring moving i.e. it will seem harder.
That's what I think anyway.
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