There is a lot of info on suspension science here...

 

Take a look at the above picture. Increasing the preload (turning the ring down) will raise the motorcycle. Bmusg, you seem to be thinking increasing the preload is like strapping the top of the shock down to the bottom of the shock. That is not true. If you simply turn the preload ring down you raise the cycle. Why would you do that? With the preload increased you can now load your cycle down with more gear and the suspension would still be at the same height as when you were riding solo. If you did not increase the preload you would bottom out after loading down your cycle.

tj315, newtons are just a unit of force. 100 pounds of weight presses down with 450 newtons of force. If you want to work with newtons fine but how ever you measure it If the spring rate is 100 pounds (450 newtons) per inch then it will take 100 pounds (or 450 newtons) to compress each inch. 100 pounds will compress one inch and 200 pounds will compress 2 inches. This is important to realize. It takes 100 pounds to compress our spring each inch. If you want to talk about newton/meters the numbers will be much smaller because inches are much smaller than meters.

Here is a link from a motorcycle suspension manufacturer that has almost the same example I talked about earlier. Except it is dealing with the front fork of a cycle. He talks about adding 100 pounds of preload by compressing the spring one inch. It still takes 100 pounds to compress each inch of travel.

http://sonicsprings.com/catalog/prel...ch_article.php

Another source:
https://en.wikipedia.org/wiki/Suspen...8motorcycle%29

Another source:
http://www.sportrider.com/suspension-setup-guide

Another source:
http://www.promecha.com.au/sag_preload.htm

In summation the preload is set to adjust the amount of sag when sitting still. If preload is not set right you will bottom out too often or you may top out too often. Preload is set to find the happy medium.

 

Imagine a 100 lb/inch coil spring sitting there, pointed straight up.

Sit upon it. If you weight 200 lbs, that spring compresses 2 inches. You can bounce up and down on it. In fact, it wouldn't be a bad spring for a bike under these conditions. A little hydraulic damping and you'd have a reasonably plush ride.

Now lets pre-load it an inch. That 1 inch compression gives 100 lbs compression in the spring.

Sit on it again with your 200 lbs weight. The spring goes does, but only 1 inch now. The first inch was in that 100 lb or 1 inch preload.

You can still bounce up and down on it, but it will "top out" a bit more easily now.

Lets make that preload adjustable by 1/2 inch each way.

So you could go with a preload of 50 lbs or 1/2 inch. Sit upon it with your 200 lbs weight, and the spring would compress 1-1/2 inch. You would have 1-1/2 inch of sag and bouncing upwards room.

If we preload it to 100 lbs or 1-1/2 inch, and sit upon it with your 200 lbs weight, the spring would compress 1/2 inch. You would only have 1/2 inch of sag and bouncing upwards room.

So in this case, preload would adjust ride height and sag, controlling how much upwards bounce was available, and how low the bike sits to the ground. The spring rate remains unchanged.

Now lets preload it 3 inches or 300 lbs. Not as crazy as it sounds, as this is all but what Harley does, especially with lighter riders.

So sit your 200 pounds of weight down on that preloaded 300 pound spring. Nothing moves. It's unmoved, fulled extended. Bounce up and down, it still doesn't move. This suspension would be effectively stuck at the top with basically no give. A very harsh and tall ride.

Lets let it be adjustable, with that same 1/2 inch.

We increase the preload, now to 3-1/2 inches or 350 lbs. Sit down on it with your 200 lbs and it of course still sits at the top unmoved. Bounce, and its just as unmoved as before. In fact, it's a little worse. Because before maybe you could move it a little by bouncing strongly, but not it's even less willing to move because you need an additional 50 pounds to compress it.

Reduce the preload to 2-1/2 inches or 250 pounds. Sit down on it with your 200 lbs weight. Again it's at the very top, uncompressed. But when you bounce on it, you can get a little bouncing action.

So in this case, while the spring rate remains unchanged, the bike height also remains unchanged, and we can make the suspension even stiffer or harder.

So, preload can indeed alter ride height like it did in the first case, and alter stiffness, as it did in the second case. It depends on how the things are put together.

 

DD, you're still wrong on this. The bike is raised because the force on the spring is pushing it up. Once you get to the limit of the shock travel, it will no longer raise the bike. Are you imagining that the shock continues to extend until it comes apart? If that's the case, take the shock off and crank down the adjusters with no weight on the shock. Does the shock come apart? No, the spring compresses. I don't have Ohlins but I'm pretty sure the height adjustment feature on the HD159 is a threaded mounting eye at the bottom of the shock. You adjust height by threading the eye in and out of the shock body, not by increasing preload. TJ or others can confirm.

 

Bmusg can you read what I am typing? Is there another language I should be using?

Here is a link just for you:http://lmgtfy.com/?q=what+does+suspension+preload+do

This quote alone shows you are not paying any attention to what I am typing:
Did you think I was talking about balloons holding up the cycle?

Lets say a big heavy rider has a passenger and luggage but the preload is not set right. His cycle would ride low and the suspension would bottom out on every bump. After adjusting the preload the ride height would be higher and he would no longer bottom out. That's the purpose of the preload adjustment, to prevent bottoming out (and topping out).

Here are my main points that are proven with the links I provided in post #82
1. Adjusting the preload does not make your suspension more firm or more soft. (Spring rate)
2. The preload adjustment changes your ride height and sag to prevent bottoming out and topping out.

Foxtrapper has a good explanation of preload and it's affect on bottoming out and topping out.
tj316 will not be logging in saying you are right and I am wrong. He read the links I provided.
Please do not reply until you check out the links I provided in post #82 or do your own searching. Oh and also please do read what I have posted. I'm not talking about a shock extending further than possible. As a matter of fact I have repeatedly said that preload affects when and if a cycle bottoms out or tops out.
After you have read, researched and understand what I am saying then reply or PM me.

 

Wow, after reading Durango Dave's post I understand what he is explaining but i'm puzzled with my own experience with my coil over's. I feel that when I add preload and raise the bike the ride feels stiffer and harsher. Why does it feel that way if what I think I'm understanding is that the pre-load only is for preventing topping and bottoming out and not regulating firmness?
I think I'm going to re-read.

 

Streetrunner- let me take a shot at confusing you more because I am not sure I know what I am talking about. When you add pre-load you reduce sag. When you reduce sag to less than 25% you are more likely to top out more often making the ride feel harsh.

 

Here's a thought experiment that may help you understand. Lets say we have a motorcycle that is heavily loaded.

Lets say, with all the weight on the cycle there is only half an inch of the shaft showing before the shock hits it's bump stop. The cycle bottoms out often when rode like this. You measure the black spring and it is 10 inches long. It is compressed this amount because of all the weight on the cycle. With less weight it would not be compressed as much. Now imagine changing preload when the cycle is loaded. (it's the wrong way to do it but helps this thought experiment) You turn the preload ring down quite a bit so there's lots of threads above the preload ring. There are also very few threads below the preload ring. Now you can see 3 inches of the shaft before the shock hits the bump stop. You get out the ruler and find out the black spring is still 10 inches long when the cycle is loaded down. How can that be? Because the spring will always be compressed that much when that much weight is on the cycle. The spring is still just as firm. It has not changed. But now the cycle is far less likely to bottom out.
If the spring is still 10 inches but the top of the spring (and preload ring) are now at the bottom of the threads on the shock what happened to the height of the cycle? The cycle is now higher when loaded down.

That is how preload works. It does not change the spring rate. It changes the ride height to make bottoming out less likely.

 

I will jump in , you are wrong , adding preload stiffens a shock and increases the rebound rate and decreasing it softens a shock and slows rebound , the fact you don't get it I'm sorry , but when you add preload and put the spring under tension not only does it then take more force to compress it but because it is under tension the spring is pushing back thus it rebounds faster , the rate however is consistent with the spring rating X the amount the spring has been compressed . Put a spring in a vise compress it a little and then yank it out of the vise and watch the action from the spring rebounding , now do it again and compress it more and yank it out , the spring will come out faster and harder and bounce around more because it has more resistance pushing back , I'm sorry you can't understand that the more a spring is compressed the more force it takes to compress it but also the harder the spring is pushing back

 

All the links you provided are basically equating stiffness to spring rate. I have never said that increasing preload changes the spring rate.

Simple question, how will the suspension that has been adjusted for 2 up (increasing pre-load) feel when the rider gets back on solo? To me it will feel "stiffer" because some of the spring deflection has been taken up by preload. If you're saying the bike will feel exactly the same no matter how much pre-load is applied, you've got different gear than I've ever dealt with.

When I bury the pre-load adjuster on my Harley Hand Adjustable shocks, the rear end doesn't jack up to increase my travel but it does ride like there is virtually no suspension at all if I'm solo. To me that is "stiffer" and all I did was increase the preload. A common complaint for Monotones is that the factory recommended 2 preload clips results in a ride that's too "stiff". I'm out.