Help me understand Pre-load

[zedXmick]

So in this example you have both sets of shocks set to a perfect sag of 150mm now you want to change your ride height. One set of shocks you have to “compromise” your perfect sag to “fake change your seat height“ The other set of shocks you are still at your perfect sag height and now you truly change your ride height by changing the length adjuster.

[bad Chad]

Thanks Huzo and company.   I pretty much get it now.  If I don’t over think it, it’s fairly easy to comprehend!

[zedXmick]

Thanks Huzo and company.   I pretty much get it now.  If I don’t over think it, it’s fairly easy to comprehend!

  

[Huzo]

Thanks Huzo and company.   I pretty much get it now.  If I don’t over think it, it’s fairly easy to comprehend!

What I find incredible, is how I have read so many articles over the years where some scribe says..
“I wound on some pre load and that firmed up the arse end...”
You could have an arse end like Serena Williams (firm), and winding on pre load’ll do nothing.
They think it was firmer because the seat didn’t drop as far when they jumped on..( the bike , not Serena...)
An idealised example, lets start with a 9” one...(wouldn’t THAT be nice.. )

A. Zero pre load +. 200 lbs load = 4” of spring compression to stabilise to a compressed length of 5”.
B. 1” of pre load + 200 lbs load = 3” of spring compression to stabilise  to a compressed length of 5”.
C. 2” of pre load +200 lbs load  = 2”  of spring compression to stabilise to a compressed length of 5”.
And so on until you could wind on enough pre load so the spring compressed 1/4” when you dragged your carcass aboard and you’d convince yourself that the suspension was as hard as a bull’s arse but not so..
The ride height has changed but..THE COMPRESSED LENGTH OF THE SPRING IS ULTIMATELY THE SAME.

In all examples, the spring “winds up” ( ) arriving at the same compressed length, but y’all will have thought examples “B” & “C” were firmer settings, ‘cos it didn’t drop as far when you clambered aboard.
Once the damper has come off the top stop (ie not topped out), the pre load you applied becomes irrelevant to the spring performance as an isolated system..
Moreover.
If the shock had no damper rod and the spring was free to expand or contract with no mechanical limitations, it can be seen more easily, that winding on pre load has zero effect on firmness...(just picture that for some time..)
So it therefore can be accepted that if the damper stays off the stops...? (No topping or bottoming out..)
The preloading has no effect other than ride height...
Hope that helps..

[Kiwi Dave]

The preloading has no effect other than ride height...

For a linear spring, yes, agreed.

[Huzo]

For a linear spring, yes, agreed.

I’ll need educating on that..

[80CX100]

A. Zero pre load +. 200 lbs load = 4” of spring compression to stabilise to a compressed length of 5”.
B. 1” of pre load + 200 lbs load = 3” of spring compression to stabilise  to a compressed length of 5”.
C. 2” of pre load +200 lbs load  = 2”  of spring compression to stabilise to a compressed length of 5”.

In all examples, the spring “winds up” ( ) arriving at the same compressed length, but y’all will have thought examples “B” & “C” were firmer settings, ‘cos it didn’t drop as far when you clambered aboard.

The preloading has no effect other than ride height...

I'm almost afraid to jump back into this,  because as I read your post, I said to myself, finally "clarity" but as I thought about it a bit more, not so much. 

ie. I'm pushing my CalVin, the refined couch that it is, hard around a bumpy corner with your setting "A" and it seems to wallow as I use up the 4" of available spring compression before I hit the firmer 5" compressed spring.

Repeat the same thing but with your setting "C" but now I only have to use up 2" of available spring compression before I feel that secure stable firm feeling of the 5" compressed spring.

The bike to me on your setting "C" feels like it is tracking and responding much more securely and decisively, much firmer ride and much less wallowing.

Am I dreaming? I don't think so, ime setting "A" can feel unsettling, vs setting "C" feels much more stable and secure.

Seems to me, that a little bit more than just ride height is being accomplished.

fwiw ymmv

Kelly

[Huzo]

I mean this in all sincerity, not to be sarcastic and I’m not hiding a swipe..
I cannot explain what my point is any other way without repeating myself.
However, there is one point of which I may make mention. The example “A” with no preload present, compared to “C” with max. preload does contain one potential difference in reality.
The “A” example allows for larger stroke on the shock/s due to the fact that it won’t “top out” as readily. This of course means that there will be more pitching motion and that will amplify any geometric changes to your bike in the dynamic environment that you describe.
That however is no more than an educated guess that I would not readily hang my hat on...

[80CX100]

The “A” example allows for larger stroke on the shock/s due to the fact that it won’t “top out” as readily. This of course means that there will be more pitching motion and that will amplify any geometric changes to your bike in the dynamic environment that you describe.

^^^^^^That makes sense, especially with cheaper older shocks with loose bushings/seals etc   

fwiw I had a bargain lined up on a new set of Ikons, because Wolfgang out in British Columbia is getting out of the biz,(will still service Ikon but no new sales once stock is gone) but he didn't have my model 

Tks for your insight and patience

Kelly

[Tusayan]

@Huzo, you have this figured out fine.  The only thing that may be missing is that with the static sag reduced by higher preload, and the shock (s) now being thereby longer when carrying a given rider, rear suspension linkage geometry may be different at the static sag position and the effective suspension rate at the wheel slightly changed by that geometry change. 

[Huzo]

@Huzo, you have this figured out fine.  The only thing that may be missing is that with the static sag reduced by higher preload, and the shock (s) now being thereby longer when carrying a given rider, rear suspension linkage geometry may be different at the static sag position and the effective suspension rate at the wheel slightly changed by that geometry change.

Things that make ya’ go
Hmmmm...

[Kiwi Dave]

I’ll need educating on that..

Take a look at a bike with a non-linear spring.  The stock V85 rear spring is such an example.

You will observe that the coils are wound tighter (less space between windings) than those at the bottom.   As the spring compresses, the top windings will close together, and therefore unable to compress any further.  This in effect creates a spring of shorter length, which has a higher compression rate.  Then it requires greater force to compress this spring further.

There's probably other forces not considered in my simple explanation, but that's how I understand it.

[Huzo]

Look that’s fine.
Also the tighter wind gives a less vertical aspect to the wire, which increases the bending moment yada yada...
What I REALLY wanna’ know is, how will pre load affect this arrangement ?
I’m developing my understanding

[93spada]

Just because I am still a little confused and not sure who is correct on ride height...….
How about some pics with measurements to prove you theory???

[Kiwi Dave]

Also the tighter wind gives a less vertical aspect to the wire, which increases the bending moment yada yada...

Them's the other forces I'm talking about, but insignificant IMHO.  Nothing's perfect.

[Tusayan]

Look that’s fine.
Also the tighter wind gives a less vertical aspect to the wire, which increases the bending moment yada yada...
What I REALLY wanna’ know is, how will pre load affect this arrangement ?
I’m developing my understanding

The effect of progressive spring rates is unaffected by preload, because as long as the shock moves any amount off the limits of its travel when the bike is loaded, the spring is no more or less compressed when preload is changed.

[Kiwi Dave]

The effect of progressive spring rates is unaffected by preload, because as long as the shock moves any amount off the limits of its travel when the bike is loaded, the spring is no more or less compressed when preload is changed.

Agreed.  That is, until the closer wound coils reach the end of their travel (hopefully not all at once).  Then the spring becomes effectively shorter, and therefore provides a greater resistance to further movement.

[Huzo]

Agreed.  That is, until the closer wound coils reach the end of their travel (hopefully not all at once).  Then the spring becomes effectively shorter, and therefore provides a greater resistance to further movement.

Yes Dave, but by then the shock has moved off it’s stops and the pre load has become irrelevant.

[Kiwi Dave]

Yes Dave, but by then the shock has moved off it’s stops and the pre load has become irrelevant.

You would not want a situation where the shock has not moved off it's stops with the rider on board.  If this situation exists, then there is too much preload wound 1n.

[Huzo]

You would not want a situation where the shock has not moved off it's stops with the rider on board.  If this situation exists, then there is too much preload wound 1n.

Well I guess so Dave, but no one suggested otherwise.

[Chuck in Indiana]

Four pages on preload? It must still be winter..

[Wayne Orwig]

Well I guess so Dave, but no one suggested otherwise.

What really matters is what oil you use in the shocks. Dino or synthetic?

 

And a couple of pages devoted to if preload changes the ride height. 

[bad Chad]

I have to toot my own horn, I’ve started a lot of far too long threads over the years!

[Huzo]

If 20 guys were chosen at random from the membership, I’m given to wonder what % would be able to explain definitively what pre load is and a few of the basic facts surrounding it...