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Discussion Starter #1
I have put this thought here, as well as in another thread, so I can get the thoughts of my peers....

Hang on a minute.....

Each click of the rear shock from 1 to 7 raises the ride height measured at the rear of my bike by 1/2 cm. (Centimeter)
The diference between the bike with me on it or off it always remains 3 cm at the same measurement point, regardless of what setting it is on.
That set me thinking.

Looking at the rear shock, (see pic) the adjustment is , to my thinking, purely ride height, not spring tension. When the suspension is adjusted through its seven clicks, it simply lifts the rear of the bike and extends the shock absorber, it does not compress or decompress the spring, as the lower surface of the ring is flat, and it has nothing to compress the spring against.
Therefore there is no spring rate adjustment on the VN, only ride height, which allows for a heavier load to not fully compress the shocker.
It seems to me that it is not possible to make the suspension "harder" or "softer", only higher or lower. To get a softer or harder ride, another spring is required. But then, why would anyone think they know better the Mr. Kawasaki when it comes to spring rate. Only my humble opinion you understand... Fire away ! VN900 rear shock absorber.JPG
The ride height increases at the rear number plate to ground by 1/2 centimetre with each click, but the movement with me on and then off is always 3 cm.
 

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Living The Dream
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I responded to the other thread you posted this in.

It is a sound theory, but the service manual suggests otherwise.

Spring Preload Adjustment
Adjuster Position 1 2 3 4 5 6 7
Spring Tension Weak ← STD → Strong


No mention of right height, but Preload Tension is exactly that, USUALLY, measured with occupants on bike. Then adjustments are made to tailor weight from there. Who really knows though?

My thought is that both theories are correct when you combine them the output is the same.
 

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Discussion Starter #3
Hi deputy loud, I love your bike.
I spent a happy half hour this evening adjusting my bog standard classic rear shocker from 1 to 7 and found, as said, that spring rate and hence softening or hardening of the ride was completely unaffected, only ride height changed. The spring length is unaltered The pic reveals the engineering behind this.
My real concern is that people will spend time trying to soften the ride doing this, which will not work.(IMHO) Being a back sufferer myself - 3 ops and pretty much no disc material at all in the lumbar spine, I feel improvements need to be found elsewhere. New tyres are much softer than old (5 years plus) ones, for example, tyre pressures (within sensible levels of course) and perhaps seats. Handlebars adjusted to give a more upright posture etc. Isn't it good that we are able to cling on to riding in advancing years on such great bikes eh?
 

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If it's that serious of an issue, one might consider a bike with better suspension (blasphemy, I know). But mono shock suspension setups do have their limitations.

I never found any real difference with mine either. Compared to air shocks, for example, where a big difference is felt when adding/subtracting air.
 

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I have heard good things about the progressive shock for the VN. $500 tho being spendy. Your explanation is about spot on. When we ride 2 up 6 is perfect, and just as good solo. Must just be the travel. We don't bottom out unless its very extreme, which I am very careful not to let happen as much as possible as we both have terrible backs as well. Thanks for taking the time and digging I to it for the rest of us. Sad thing is tho some may need to upgrade. But mine has a better suspension than my Electra glide which I did upgrade to progressive. It's better but still not great. Must be the extra weight. But we carry just as much on the Vulcan at times. Who knows, but I do say it is a decent factory shock for sure.
 

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Sailor V
You are correct your not adjusting the spring rate. Spring rate is a constant, its the weight required to move the spring 1 in or 2.54 cm. What you are doing is preloading the spring which as you noticed raises the ride height as well.
And you mention the spring is not compressing due to design and spring length. If the spring had nothing that allowed it to compress it would just slide off the shock. As for the spring length not changing is this measurement being taken with the shock mounted or off the bike. If its off the bike mount it and you may be surprised.
Now as for the bike moving 3cm no matter what notch its on measured from the same point. If the first notch is point zero the the bike will lower -3 cm. Now if you go to the top notch which raises the bike 2.5 cm and then the bike will only be at -.46 cm so the bike is still 2.5 cm higher. That should prove the spring is getting stiffer because if nothing changed in the adjustment then the bike would drop like it was set on the first notch.
Hope that all made sense
 

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Thanks for making a separate thread. Here was my last post from the other thread, comments welcome:

Well you have my attention (sailorV), but without launching my own investigation the only hole i can definitively poke in your theory is that i can tell a big difference in rear end stiffness when i crank it up. Its firmer on bumps, less wallowing in hard corner exits, and the front and rear suspension become out of sync. That last part is something i learned to detect from sportbikes. Basically when you go over a section of road i call a washboard or series of small bumps/roughness if one end is stiffer than the other the bike does not recover as quickly. It can actually amplify the bumps if the front and rear suspension are far enough apart. All these things change when you crank that dial. A little bit of ride height will effect corner entry, ability to hold a line in a corner, and corner exit, but should have little effect on the previous things i mentioned. So im not necessarily dismissing your findings, im now simply wondering how could the bike achieves the effect without ever changing the preload.

I like 6 for a good firm setting, but I think 5 would give better performance on the washboard sections of road since there isn't an adjustment for the front. Not really an issue unless you encounter a washboard in the corner then you will be wishing for the bike to settle down asap. I may go back to 5 and give it a try.
 

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I'm no physicist but intuitively if you tighten the preload then the spring metal is under greater "stress" and so will resist bounce more. Does that make sense?
 

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Sorry this is so long but here goes:

...When the suspension is adjusted through its seven clicks, it simply lifts the rear of the bike and extends the shock absorber, it does not compress or decompress the spring...
Sailor V
You are correct your not adjusting the spring rate. Spring rate is a constant, its the weight required to move the spring 1 in or 2.54 cm.
Let's assume you are both correct, which basically, you both are. Motorcycle suspensions are designed so that the springs are always under compression, even when fully extended. Pre-load is used to adjust the initial position of the suspension with the weight of the motorcycle and rider acting on it.

The difference between the fully extended length of the suspension and the length compressed by the weight of the motorcycle and rider is called "total sag" or "race sag". Total sag is set to optimize the initial position of the suspension to avoid bottoming out or topping out under normal riding conditions. "Bottoming out" occurs when the suspension is compressed to the point where it mechanically cannot compress any more. Topping out occurs when the suspension extends fully and cannot mechanically extend any more. Increasing pre-load increases the initial force on the spring thereby reducing total sag. Decreasing pre-load decreases the initial force in the spring thereby increasing total sag. When you increase the preload length, you are indeed increasing the initial force exerted by the springs. This decreases sag, making the bike ride higher. It does not, however, increase the spring rate. (This is where Mex is correct)

But it does make the ride stiffer. And here's why:

Shock absorbers are basically oil pumps. A piston is attached to the end of a piston rod and works against hydraulic fluid in the pressure tube. As the suspension travels up and down, the hydraulic fluid is forced through orifices (tiny holes) inside the piston. Because the orifices only allow a small amount of fluid through the piston, the piston is slowed which in turn slows down spring and suspension movement. Now, as Sailor V stated, when you adjust to the "stiffer setting" of 7, it extends the shock and raises ride height. When you extend the shock, there is more fluid in the pressure tube meaning when the shock is compressed during a bump, there is more pressure against the piston from the fluid in the pressure tube pushing in the opposite direction making the ride harder or stiffer. So basically, both of you were correct in your own ways.

I hope that helps explain why adding preload raises the ride height, and as a result makes the ride stiffer.
 

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Sorry this is so long but here goes:





Let's assume you are both correct, which basically, you both are. Motorcycle suspensions are designed so that the springs are always under compression, even when fully extended. Pre-load is used to adjust the initial position of the suspension with the weight of the motorcycle and rider acting on it.

The difference between the fully extended length of the suspension and the length compressed by the weight of the motorcycle and rider is called "total sag" or "race sag". Total sag is set to optimize the initial position of the suspension to avoid bottoming out or topping out under normal riding conditions. "Bottoming out" occurs when the suspension is compressed to the point where it mechanically cannot compress any more. Topping out occurs when the suspension extends fully and cannot mechanically extend any more. Increasing pre-load increases the initial force on the spring thereby reducing total sag. Decreasing pre-load decreases the initial force in the spring thereby increasing total sag. When you increase the preload length, you are indeed increasing the initial force exerted by the springs. This decreases sag, making the bike ride higher. It does not, however, increase the spring rate. (This is where Mex is correct)

But it does make the ride stiffer. And here's why:

Shock absorbers are basically oil pumps. A piston is attached to the end of a piston rod and works against hydraulic fluid in the pressure tube. As the suspension travels up and down, the hydraulic fluid is forced through orifices (tiny holes) inside the piston. Because the orifices only allow a small amount of fluid through the piston, the piston is slowed which in turn slows down spring and suspension movement. Now, as Sailor V stated, when you adjust to the "stiffer setting" of 7, it extends the shock and raises ride height. When you extend the shock, there is more fluid in the pressure tube meaning when the shock is compressed during a bump, there is more pressure against the piston from the fluid in the pressure tube pushing in the opposite direction making the ride harder or stiffer. So basically, both of you were correct in your own ways.

I hope that helps explain why adding preload raises the ride height, and as a result makes the ride stiffer.
I have no idea if there is fluid in the shock or not but sorry, this statement is false. "When you extend the shock, there is more fluid in the pressure tube meaning when the shock is compressed during a bump, there is more pressure against the piston from the fluid in the pressure tube pushing in the opposite direction making the ride harder or stiffer." Rather than try and explain hydraulics, which I've specialized in for 30+ years, fluid is virtually incompressible so it's impossible for it to increase pressure in this case since it's resistance doesn't change. The amount of fluid on the piston side is immaterial, unless of course it bottoms out. What it will allow is for a longer stroke, which begs another question. Is the spring a constant pressure spring? ;) In this case it's highly unlikely. Without disassembling a shock I'd have to say raising and lowering the shock is all that it's basically doing to make allowances for additional weight.
 
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