Pre load..(again)

[Huzo]

Here we go…
A linear spring with your bike on its wheels may be say 12” from eye to eye. When you get on it will compress to say 10”.
So the ride quality of THAT spring will be a given state.
Now.
If you stayed on your bike and someone wound the perch up from the bottom 1”, then the spring would undergo a compression and push the top collar away by 1”, so the spring was at the same compressed length as before the adjustment was performed.
It has to be, because the spring is supporting the same weight, it’s just that the now compressed spring is 1” vertically upwards. But because the spring is in EXACTLY the same state as before the preload adjustment, it will perform exactly the same.

So we should be at ease with the concept that alteration of preload on a linear spring DOES NOT ALTER SPRING RATE, therefore ride quality.

So if we move to our progressive spring model.
It is certainly true that application of load will be taken up first by the tighter wound spring which has a “gentler” rate, progressively moving onto the higher rate coils as it compresses.
No arguments there…However.
Winding on 1” of preload will only start compressing the spring against the load and the spring top will start to extend the damper rod until again, spring force = load.
The spring will be the same compressed length after preloading as before.
The spring was supporting a given load BEFORE  the preload adjustment and it supporting the SAME LOAD after the adjustment.
The weight has not changed.
Now linear or progressive, if the compressed length is the same, then the spring performance is the same.

Now of course if preloading your spring on the centrestand has shortened it’s (unladen) length then some of the travel has been used, so when you jump on instead of it sagging 1” to achieve it’s compressed length, it will only sag 1/2” to achieve that length.
But the compressed length will be the same, so the ride quality will also be the same.
Linear or progressive.

Test it yourself…
Measure eye to eye on your progressive spring with you on board, let’s say it’s 10”
Now wind on 1/2” of preload, get back on and re measure…It will still be 10” eye to eye, but there will be 1/2” more damper rod exposed.
That will not have changed the performance characteristics of your spring.

[faffi]

I straight spring will always compress a certain amount for any additional load of the same magnitude. However, there are some extra things to consider.

Negative wheel travel:
If you add preload until no sag, the ride will be harsh because the suspension cannot extend the wheel to take up dips. You will gain ride height this way, which will alter the geometry..
If you have too little preload, sag will be excessive, causing frequent bottoming over bumps and again a harsh ride. You will lose ride height this way, which again will alter the geometry.
If you have progressive springs, you will basically adjust the softer part of the springs, altering overall springrate; more preload = stiffer overall springrate.

Hence preload have impact on comfort and handling. Finding the right spring rate, damping rate and preload for your conditions will greatly enhance the riding experience.

[tazio]

Good read, thanks.

Now, off topic, but....
Question, what is being accomplished when varying the amount of fluid in your forks?

[Huzo]

Good read, thanks.

Now, off topic, but....
Question, what is being accomplished when varying the amount of fluid in your forks?

I would contend that because damping is achieved by the action of fluid through  an orifice, as long as the valves are below the level of the fluid, then it makes no difference.
This would not be allowing for the air gap above the fluid level which will provide some assistance to the spring.
How much or little of this effect comes into play is beyond me.
Also the more fluid present, the more fluid mass you have to dissipate heat through frictional considerations.

[n3303j]

I was under the impression that the only purpose for the height adjustment on the spring was to allow centering a loaded bike on the travel range of the shock absorber. Object being to avoid topping or bottoming out the shocks on road irregularities. It was not to alter ride "quality".

[inditx]

I remain amazed at the brain trust here on such topics but must admit that my head hurts.
I know it shouldn’t be that hard but it just makes my head swim. BTW, you need a good buddy to help with all of this. To this end I had Ace adjust my Eldo suspenders but the stock shocks just weren’t great for me anyway.

Thankfully youse guys and the manufacturers sometimes, take this into account, hence electronic suspension and such for those of us that just can't seem to wrap our small brains around suspenders and their adjustment.

Now having said all that, I do have aftermarket shocks and fork modulators on my CB1100 and have adjusted them to my ability and am still not happy. The V85 is adjusted and work as well as I can reasonably expect I suppose.

Next bike, electronic suspenders of some sort.
My.02, YMMV
inditx

[PeteS]

Good read, thanks.

Now, off topic, but....
Question, what is being accomplished when varying the amount of fluid in your forks?

It depends on the design and sophistication of the forks. Forks with only rebound damping adjustment primarily depend on the valve opening or in primitive forks just a hole in a tube so minimal effect of the amount of fluid. It will affect compression damping though as more fluid means less air space so compression damping is increased (stiffer ride). Opposite effect for less fluid.

Pete

[kingoffleece]

Electronic suspension can often be lots of compromised choices vs one correct choice by using properly designed and set up product(s).

[SemperVee]

 keeping all this mind as I need to "find" a decently priced stock for my 07 Norge come this spring.    It is shocking that a new single rear shock costs about  40-50% what my bike is worth -  should I ever decide sell it.

[Huzo]

I was under the impression that the only purpose for the height adjustment on the spring was to allow centering a loaded bike on the travel range of the shock absorber. Object being to avoid topping or bottoming out the shocks on road irregularities. It was not to alter ride "quality".

That is absolutely correct.

[faffi]

It depends on the design and sophistication of the forks. Forks with only rebound damping adjustment primarily depend on the valve opening or in primitive forks just a hole in a tube so minimal effect of the amount of fluid. It will affect compression damping though as more fluid means less air space so compression damping is increased (stiffer ride). Opposite effect for less fluid.

Pete

Actually, as Huzo mentioned above, oil volume affect spring rate, while viscosity affect damping. With zero gap (fork filled to the top), there will be zero wheel travel since fluid cannot be compressed. In other words, you will need at least as much air volume as the fork oil disposed of under full travel, plus a tiny margin (air cannot be compressed to zero) in order to have full wheel travel. The bigger the air volume (air gap) you have, the less affect the air spring effect will have on the overall spring rate of the fork. Adjusting the air gap to suit your preferences and load can give you a supple ride without bottoming.

Anybody wanting to learn a lot about suspension will benefit for Race Tech's "Suspension Bible". Getting the damping correct for the spring and your riding/bike can give better grip, less tire wear, more comfort and better handling. But usually, one must make sacrifice in one area in order to optimize another.

[Huzo]

With your progressive spring, when you first jump on, your weight takes the spring the first 10%
If you wind 10% of preload on from the get go, you are still at 10% when you jump on, but you won’t sag to get there. Once the spring comes off the top stop under load, it is only the load that is compressing it.
It’s just that the travel started from a different point.
See how the spring state is the same in both examples ?

Maybe this will help.
If your total load = preload + payload and that compresses your spring 3”
Zero preload will mean when you jump on it’ll compress 3”
Or.
Wind on 3” of preload then jump on and it’ll not compress at all..(but your ass will tell you the spring is “stiffer”)
In both cases your spring is compressed 3” from rest, so it will behave the same.
Don’t muddy the water by trying to factor in which coils are doing what…It is the TOTAL compression that you’ve achieved under the applied load.
When your spring is preloaded and you are on board, it is not 3” of preload PLUS 3” of payload, your spring will compress FROM THE POINT where the preload took it.
It is the initial preload PLUS whatever it took to get it to 3” of compression, either way, you arrive at the same place compression wise, so therefore the same performance.