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Thread: Diavel suspension is too firm

  1. #46
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    Quote Originally Posted by Cosmik de Bris View Post

    That's what I think anyway.
    I have a rear shock out of a 1998 CR250 here for a rebuild. If I wind the preload collars right off, I can compress the shock myself (a wee bit only) by just pushing down on it. If I was to wind the collars right up, I couldn't budge it no matter how hard I might try. So it's softer one way, and harder the other. So for people to say preload makes no diffence to how the shock/bike behaves, and is no softer or stiffer is simply not correct.

  2. #47
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    Quote Originally Posted by Cosmik de Bris View Post
    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.
    I think I'm wrong again. The force to move the spring a unit length is constant, so it shouldn't seem harder. Will someone release me from this hell!

  3. #48
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    Quote Originally Posted by Cosmik de Bris View Post
    I think I'm wrong again. The force to move the spring a unit length is constant, so it shouldn't seem harder. Will someone release me from this hell!
    LOl. Yeah, a 50kg spring, is a 50kg spring. NOTHING changes that. But see my post above yours.

  4. #49
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    Quote Originally Posted by SVboy View Post
    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.
    Took some preload out of my TZR/FXR bucket setting it to the "recommended" bike + rider static sag and went out for a few laps.
    Was peg down on the first corner I went around with cold slicks... Lets just say I went back to the pits and wound that bitch right up again

    Pre-load is just that, it's what we do when we go out for a night on the town, we load ourselves up with piss but we still only have the same amount of stomach to contain it .

  5. #50
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    Quote Originally Posted by Crasherfromwayback View Post
    I have a rear shock out of a 1998 CR250 here for a rebuild. If I wind the preload collars right off, I can compress the shock myself (a wee bit only) by just pushing down on it. If I was to wind the collars right up, I couldn't budge it no matter how hard I might try. So it's softer one way, and harder the other. So for people to say preload makes no diffence to how the shock/bike behaves, and is no softer or stiffer is simply not correct.
    Exactly, I'm guessing it's down to the sprung forces (I'm shit with this stuff), the more it's compressed the more force it is pushing out, therefore you could say that it's harder because the force it's pushing out is more. Actions, reactions, stuff... I'll revert to my real job now: Have you tried turning it off and on again?

  6. #51
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    Quote Originally Posted by Bass View Post
    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.
    Static sag. As a point regarding stiffness, the R6 was sitting totally at the top of it's travel, and when being ridden over small bumps at low speed, it felt rigid, like it was coil bound. Back it off, give it some static sag, and it's soft enough to absorb those same bumps. It'll still only take the same force to bottom the shock out, so it's obviously not making it softer all the way through the stroke, but the first 1/3 odd of the travel? Hell yes.

  7. #52
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    Thank you team, I can see where you are coming from with preload changing ride height.

  8. #53
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    Quote Originally Posted by SVboy View Post
    Thank you team, I can see where you are coming from with preload changing ride height.
    Most def. Very important. On my RS250, even a few mm's would change things quite a bit. The model after mine, had the single sided swing arm and an eccentric cam, chain adjuster. So every time you adjusted chain tension, your ride height settings went out the window as well. Pain in zee backside.

  9. #54
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    This discussion is bouncing all over the place. You all need to dampen down your tone so we can rebound back to the topic in question - a sore bum. The first thing that springs to mind whenever I hear people bleating on about their bike needs this and that done to their suspension is; are you really pushing your bike to the limits to warrant spending heaps of $$$ on a luxury you may never actually benefit from. I've met so many riders who obsess with suspension tuning yet ride like a big blouse, too scared to rev beyond idle and no idea why bike tyres have tread on the sides. Never pushed their suspension anywhere near it's limitations.

    Sounds like the OP is concerned about bum comfort. Deflate your tyres or sit on a sheepskin rug.

    In saying that it is ironic that for the first time in decades I'm changing my current bikes shock for a better one. But that is after 3 months of serious hard riding to get to know it and too many scary moments that have convinced me I'm playing Russian roulette.

    If you ride heaps and it does sound like you have tried all possible variations with the OEM then yeah, change bikes or change the suspenders.

    Apologies if it sounds like I did some preloading before writing this.
    Happiness is a means of travel, not a destination

  10. #55
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    Quote Originally Posted by MD View Post

    Apologies if it sounds like I did some preloading before writing this.
    Makes perfect sense to me.

    Click image for larger version. 

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  11. #56
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    here is my take on it.You cant"preload" the spring.You wind up the preload and you are trying to push the top of the spring up.There is no extra force to push the spring down so the rear of the bike raises by 5mm or whatever.And another 5mm next time ....and so on.However there is a limit to that travel,and it is the length of the shock itself.Not sure but i guess the the logical end of the preload adjustment wwould actually have the shock topped right out.Preload is never a term i could figure..its ride height adjuster.It also steepens the head angle and alters the geometry of the rear suspension a little bit.
    Springs are a well known science.Its probably oversprung.It wouldnt be much(in the scheme of diavels and ohlins) to get a new spring wound with a more sutable rate.I am sure Mr Taylor will have some ideas before a purchase of a Ohlins is actually required. The existing shock may be able to be revalved.
    Eccentric chain adjuster need to be adjusted so both halves are turned at once so the adjustment can be made without affecting the height

  12. #57
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    Quote Originally Posted by BMWST? View Post
    Eccentric chain adjuster need to be adjusted so both halves are turned at once so the adjustment can be made without affecting the height
    On an old GPZ1100 etc like my old one, it still changed things. But on the RS250, with the single sided swing arm, there is only the one cam. Adjusting the chain automatically changed the ride height.

  13. #58
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    Quote Originally Posted by Crasherfromwayback View Post
    On an old GPZ1100 etc like my old one, it still changed things. But on the RS250, with the single sided swing arm, there is only the one cam. Adjusting the chain automatically changed the ride height.
    Yes i remember a kawasaki model iwas interested in(gpz 900?) and i thought that by rotating both the inner and outer eccentrics at the same time would move the wheel back but not raise the axle?

  14. #59
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    Quote Originally Posted by BMWST? View Post
    Yes i remember a kawasaki model iwas interested in(gpz 900?) and i thought that by rotating both the inner and outer eccentrics at the same time would move the wheel back but not raise the axle?
    No. The axle went through both eccentric cams, on either side of the swing arm. Chain tension was adjusted, by rotating said cams, together, after backing off the pinch bolts on each swing arm *leg*. So to make that fat old bus turn a lil quicker, you'd rotate them 180 deg to lift the back end up. The same needs to be done with my old Slabbie. It's single shock (obviously), but the lower shock mount is also on an eccentric cam. Lift them up!

  15. #60
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    Sorry...forgot the pic...

    Click image for larger version. 

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