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Offline halbie

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Re: Rear shock preload
« Reply #10 on: May 09, 2019, 11:44:59 PM »
Ove,

I think this guy's explanations are good, and here's one discussing your questions: https://lifeatlean.com/teach-me-suspension-everything-preload/

And if you want to go deep, dig around here and watch some of his videos: https://davemosstuning.com

Offline Bruno

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Re: Rear shock preload
« Reply #11 on: May 10, 2019, 03:22:45 AM »
Andy is correct. Changing preload does not compress the spring (when the shock is mounted on the bike). And it never changes spring rate. Think about when you increase preload ie wind the collars towards the spring (note- shock is mounted on bike). The piston on the shock is free to move. The weight acting on the shock (the bike) does not change. So as you wind the collar towards the shock, the piston just moves out since thereís no restraint on it. Thus the seat rises. Spring length is unchanged. This is different when the shock is off the bike. Piston is bottomed out so it canít move. In that case, adding preload does compress the spring. It doesnít matter because when you mount the shock again, the spring compresses to the same length ( due to the weight of the bike).

 What you want to aim for is it when the rider - or rider and pillion - are on the bike, the shock compresses to the point where 1/3 of its max travel is being used - that leaves 2/3 travel to soak up bumps when riding. it means the shock  shouldnít  bottom out over harsh bumps.  If when you sit on the bike the shock compresses too much and too much travel is used and you canít adjust it back with the preload ring then you need A heavier spring.  Likewise if the shock doesnít compress at all and you canít adjust it to get 1/3 of travel then you need a lighter Spring.  And donít take the shock off the bike  to adjust the preload as it shows in the manual - thatís just a waste of time.   
*Originally Posted by Andyb1962 [+]
Please ignore the manual itís ď###Ē
The preload will alter ride height only . Not tension or stiffness . What ever itís rated at it will stay the same .
But yes as above to increase preload

Back off locking ring
Turn adjust ring clock wise to increase preload
Reset locking ring .

Please read all other posts on suspension some really good explanations

Offline Oop North John

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Re: Rear shock preload
« Reply #12 on: May 10, 2019, 06:36:36 AM »
*Originally Posted by luishcorreia [+]
Increasing preload will lower ride height, righ? As them spring is more compressed?

No in a word, see later post in this thread for why.

Offline Nibs

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Re: Rear shock preload
« Reply #13 on: May 10, 2019, 07:55:19 AM »
Thanks all, useful advice. Iíll try and set the preload up tonight as Bruno recommends.
Nick
Z900RS Cafe & CB1100RS

Offline Ove

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Re: Rear shock preload
« Reply #14 on: May 10, 2019, 08:08:45 AM »
*Originally Posted by Bruno [+]
Andy is correct. Changing preload does not compress the spring (when the shock is mounted on the bike). .... So as you wind the collar towards the shock, the piston just moves out since thereís no restraint on it. Thus the seat rises. Spring length is unchanged. ..... when you mount the shock again, the spring compresses to the same length ( due to the weight of the bike).

 

So in essence, the preload adjustment is like adding a spacer, without affecting spring tension. What I don't get is why it makes any difference for when you have a pillion? If before increasing ride height you used 1/2 spring with a pillion aboard, wont it be the same after adding preload, you'll just be a bit higher up  but still with half the spring used up?

I will check the links this evening and thanks for posting.

Offline Bruno

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Re: Rear shock preload
« Reply #15 on: May 10, 2019, 11:32:38 AM »
We were talking before about free sag (Weight of the bike only). The spring is compressed slightly (compared to when the shock is off the bike). When mounted, The weight of the bike moves the shock piston into the shock body. Letís say it uses up 15% of the max travel. This is due to the weight of the bike. Free sag doesnít really matter and you donít adjust it. We care only about rider sag. When you sit on the bike (in full gear, feet off the ground), you want 30% of the travel to be used up. And so when you get on the bike, spring is compressed more. Letís say 50% of travel is now used up. Adjust (add) preload to get back to your 30% of travel point. Again, when adjusting preload, spring compression does not change. That only changes when the load changes (eg when you get on). By winding the preload ring towards the shock body you are simply driving the piston out of the shock. This makes it longer. Rear of bike rises. Ride height increases.

So once you have set your rider sag to 30% of shock travel, you are good. Now when the pillion gets on, load on the spring increases, it compresses, piston moves into shock body more, and more shock travel is used - lets say to 50% of max. To correct this , you add preload. In reality, when my wife gets on the back and we go to the pub, I donít mess about  changing  preload. If I were doing a track day with her on the back I would. So yes you are correct- adding preload with a pillion on board does not change spring compression - it just moves the piston out of the shock body and increases ride height. Just like when you add preload to the forks - you donít compress the spring, you just push the sliders out of the stanchion more.
*Originally Posted by Ove [+]
So in essence, the preload adjustment is like adding a spacer, without affecting spring tension. What I don't get is why it makes any difference for when you have a pillion? If before increasing ride height you used 1/2 spring with a pillion aboard, wont it be the same after adding preload, you'll just be a bit higher up  but still with half the spring used up?

I will check the links this evening and thanks for posting.
« Last Edit: May 10, 2019, 11:53:15 AM by Bruno »

Offline Bourbon

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Re: Rear shock preload
« Reply #16 on: May 11, 2019, 01:09:50 AM »
*Originally Posted by Bruno [+]
We were talking before about free sag (Weight of the bike only). The spring is compressed slightly (compared to when the shock is off the bike). When mounted, The weight of the bike moves the shock piston into the shock body. Letís say it uses up 15% of the max travel. This is due to the weight of the bike. Free sag doesnít really matter and you donít adjust it. We care only about rider sag. When you sit on the bike (in full gear, feet off the ground), you want 30% of the travel to be used up. And so when you get on the bike, spring is compressed more. Letís say 50% of travel is now used up. Adjust (add) preload to get back to your 30% of travel point. Again, when adjusting preload, spring compression does not change. That only changes when the load changes (eg when you get on). By winding the preload ring towards the shock body you are simply driving the piston out of the shock. This makes it longer. Rear of bike rises. Ride height increases.

So once you have set your rider sag to 30% of shock travel, you are good. Now when the pillion gets on, load on the spring increases, it compresses, piston moves into shock body more, and more shock travel is used - lets say to 50% of max. To correct this , you add preload. In reality, when my wife gets on the back and we go to the pub, I donít mess about  changing  preload. If I were doing a track day with her on the back I would. So yes you are correct- adding preload with a pillion on board does not change spring compression - it just moves the piston out of the shock body and increases ride height. Just like when you add preload to the forks - you donít compress the spring, you just push the sliders out of the stanchion more.

Free sag is important though.  You do not want to end up with no free sag.

I believe you want somewhere around 10% free sag and around 30% rider sag.

Offline Bruno

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Re: Rear shock preload
« Reply #17 on: May 11, 2019, 03:20:36 AM »
*Originally Posted by Bourbon [+]
Free sag is important though.  You do not want to end up with no free sag.

I believe you want somewhere around 10% free sag and around 30% rider sag.

I agree - when rider sag is correctly set at 30% there should be some free sag. If there is none it means the spring is too soft. But you donít want to set free sag with the preload - only rider sag. I did 3 track days on an RSVR with stock Ohlins suspension and the spring was too soft - no rear sag. But I could run mid A group even on that slow bike, and I hadnít been on track for 30 years. So while some free sag is good itís not critical as long as rider sag is set.

Offline Ove

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Re: Rear shock preload
« Reply #18 on: May 11, 2019, 03:48:05 PM »
*Originally Posted by halbie [+]
Ove,

I think this guy's explanations are good, and here's one discussing your questions: https://lifeatlean.com/teach-me-suspension-everything-preload/

And if you want to go deep, dig around here and watch some of his videos: https://davemosstuning.com

Good article. Thanks

Offline Mike

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Re: Rear shock preload
« Reply #19 on: May 16, 2019, 04:36:56 PM »
No matter what length you compress the spring to the force required to compress it when riding stays the same . All preload does is set the sag height when you sit on the bike .