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adjusting rear spring,, where to start?

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Posted by: Nevada Sixx---------------------

hi,,i need to set my spring preload on my rear shock, right now it has no tension on it.. how far down should i adjust the tension to start off with?

if im not mistaken, your bike should squat down a few inches when you sit on it,, but before you sit on it, should the bike be at this natural squat after the last time you sit on it, or should i pick up on the rear end first before i measure, and sit back on it? thanks.


Posted by: marcusgunby---------------------

Preload the spring by 10mm as a baseline then measure from there-i go for 95mm sag (when you sit on it compared to it measured on the stand) then you measure the sag with just the weight of the bike acting on the spring(free sag)it should be around 25mm compared to the extended measurement of it on the stand.

so preload the spring 10mm
then measure it when on the stand
then sit on it and have a friend measure-adjust if necessary to 95mm
then measure it on its own off the stand and compare to on the stand-difference shoudl be about 25mm-then ride and if it steers to sharp or knifes or headshakes then increase to 100mm of sag.


Posted by: Nevada Sixx---------------------

i heard too much preload can make a bike kick to side coming off jumps,, have you heard that also?


Posted by: marcusgunby---------------------

I guess it depends on how extreme we are talking-a major amount of preload(ie the shock tops out when the bike sits uner its own weight) would cause a few problems.Im not sure i would say kicking to the side is the main problem-then again i havnt tested to the extemes as i generally try to get springs close to my needs.

That sounds more like a rebound problem-however its so hard to diagnose something on the net as i cant see or ride the bike-i generally like to ride a bike with a certain problem as its very hard to get consistant feedback.I stuggle to give myself good feedback 50% of the time


Posted by: RemeberMe---------------------

Quote:
Originally posted by marcusgunby
Preload the spring by 10mm as a baseline...


How is this accomplished, and where is the measurement taken from?


Posted by: Jeremy Wilkey---------------------

Quote:
Originally posted by marcusgunby

That sounds more like a rebound problem-however its so hard to diagnose something on the net as i cant see or ride the bike-i generally like to ride a bike with a certain problem as its very hard to get consistant feedback.I stuggle to give myself good feedback 50% of the time



Marcus,
Why is that a rebound problem? Everyone allways say rebound.. The reason why I belive comes down to when they adjust the rebound slower (Whateveryone allways does) the problem is reduces only so far as the bike just becomes more ridgid. So the guy who rides his bike to test dose'nt actually see the real problem.. Althought I could see it being rebound problem in some circumstances compression is more likely the issue with a kick to the side off a jump.

If you want to think about it from a probabilty standpoint, rebound only controls the reaction of the trapped energy in a spring. The compression must be acted on first, so in a single bump, the occurance of a rebound problem is less likely.

Anyway, diagnossing suspension problems is both hard and easy... Once you can know the condtions under which something ocurs then you can reconstruct the forces acting on the suspension, and if you do that acurately enough your "money"..

BR,
Jer


Posted by: marcusgunby---------------------

To preload the spring measure it when the collors are loose on the shock then tighten down the collors until its 10mm shorter.

Jer i was thinking of if the rebound is too stiff it may be packing on any bumps on the face of the jump and then having no travel left to absorb the reaction as it hits the take off.Or i was thinking rebound too fast and it was like a pogo stick.

Do you think its a case of to little compression?


Posted by: Jeremy Wilkey---------------------

Quote:
Originally posted by marcusgunby

Do you think its a case of to little compression?



Why not solve the problem at its root... I'd hate to screw up the performance somewhere else on the track..


Posted by: marcusgunby---------------------

Jer a little story if you dont mind
A friend of mine has a 96KX125-just started racing-complains of the rear having no traction-he has opinions of everyone and there dog-answers of rear tyres no good to bad throttle control-so i said lets not try to work this out and let me look at the shock 1st to get one thing eliminated.

I strip the shock-its never been serviced-in 7 years, the oil is like water and its full of air-sounds like sandpaper.Well inside its looking nice the bladders hardly worn and no damage.I build it up with fresh oil and it feels nice again-moral of the story is you have to ensure everything is mechanically sound as a 1st step or you can chase symptoms till your blue in the face.


Posted by: RemeberMe---------------------

I've had that exact same problem all summer with my '02 CR250 - everytime I try to jump big the bike always kicks to the side...it's caused two pretty nasty wrecks. I tried dialing it out by softening the rebound, but that didn't work. Then I thought it was just me, but the last two times I've ridden I've steered toward the idea that the bike isn't set up. I'm definately NOT Money! It'll be two or so months before I get to ride again, so maybe then I'll try adjusting the compression.

Jeremy, I read "too little compression" coming out of your posts, right? Any other useful hints for a 170lber (w/gear) on an 02 CR250? Thanks for the insight, I'm still new to this riding thing, and ever newer to the suspension tuning aspect of a bike.

Thank you,
Andrew

P.S. Thanks Marcus for explaining the proper technique for spring preload.


Posted by: Nevada Sixx---------------------

isnt 10mm only about a 1/2 inch?

also,, i know my bikes rear shock leaks oil, so maybe i got no rebound dampening left to adjust with clickers,,, but getting back to setting the spring from scratch,, i sould just tighten it down about 1/2 inch,, and that's about the average that people run?


Posted by: marcusgunby---------------------

Nevada Sixx if your shock is leaking oil please do not ride it anymore-it is very unsafe and also will wear the shock internally very fast to the point it will cost a fortune to repair-trust me on this, i have nothing to gain by giving this advice.

Once fixed set the preload to 10mm as a starting point only-this is just to stop you having to wind the spring down on the threads for ever and a day.Then set it up as per instructions.



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