measure sag, go for 30%, then add compression to desired value in dhx2 guide. Without compression damping it will bottom out easily.

Preload wont stiffen your spring. Its just for control sag value. If you still bottoms harsh get stiffer spring. Im sure dhx2 has pretty hard rubber bottom out. I just couldnt bottom it out harshly with proper compression damping. Moreover it was using full travel with bottomless feeling.

 

I just couldnt bottom it out harshly with proper compression damping. Moreover it was using full travel with bottomless feeling.

I don't feel a hard bottom out either. I only know it's happening because of the indicator. I pretty much feel bottomless too. So I'm not sure my concern is warranted. I just know I'm bottoming much more frequently and easier than on my air springs. But maybe this is to be expected since coils are more linear and don't require a massive hit to blow through that last little bit of the stroke.

 

Preload wont stiffen your spring. Its just for control sag value.

Yes, it will, effectively.
Take a fork spring for simplicity, i.e. 1:1 rate.
Say you preload it by 5mm.
Then, on a 160mm stroke fork, at full compression that spring is going to be effectively compressed through 165mm rather than 160mm.
E.g. 45lbs/inch spring = 1.77 lbs / mm
283lbs to compress through 160mm.
292lbs to compress through 165mm.

Not only that, increasing preload will put the rider in a less forward leaning position, also effectively making the spring feel stiffer for him or her.

Note: Apologies for reviving old thread, I was reading up on this, but keep coming across this erroneous claim.

 

italians.... it wont change stiffnes. preload just elevates whole line. stiffnes is still the same in newtons per milimeters.

The spring rating stays the same. e.g. 45Lbs/inch. But to compress the fork in my example to full extension after preload requires a greater force than before preload. I.e. It is stiffer in the application it is being utilised in.

 

The spring rating stays the same. e.g. 45Lbs/inch. But to compress the fork in my example to full extension after preload requires a greater force than before preload. I.e. It is stiffer in the application it is being utilised in.

Bro, you are just confusing everyone by pretending that "stiffness" means a different thing. Replace your word "rating" with the word "stiffness" like a normal person who speaks English and the argumentation will evaporate.

 

generaly air shock can use less hsc damping, cuz it has natural progression of air spring. In coil you have to use more hsc to prevent harsh bottoming. If you use all your travel without feeling it, its ok. I would add I was using more hsc and less lsc than in dhx2 shock guide.

 

I also wonder if perhaps my rebound damping is too high, and the bottoming I'm seeing is related to packing. That should be pretty easy to test.

 

Frequency determines spring-rate. Preload determines ride-height (geometry) and damping is used to take out bump energy.

Have a go through this: http://forums.mtbr.com/shocks-suspension/1-sheet-setup-guide-1084380.html

 

I think the drop test in the video overlooks normal rider weight that overcomes the spring preload ‘bounce’ that is observed with an unloaded rear end

 

@ ronank The discussion started with a rear shock spring preload question. To preload a 65m stroke spring 5mm isn't going to get you much at bottom out so your example of a 160mm stroke fork spring isn't valid. And even if you want to use that example it is less than 3% stiffer at bottom out which will be insignificant if you've already used 160mm of travel.

 

Pre-load sets ride height (sag), nothing more, nothing less.

If you're bottoming out too often, you need a spring with more spring rate, 600 vs. 500 or whatever. Increasing pre-load doesn't effect the spring rate.

.

 

This was still bugging me, so I sketched it up.

 

A coil spring is effectively linear, so if it takes X pounds to compress it 1 inch, it then takes an additional X pounds to compress it another inch. It doesn't matter where you start in the travel, it will still take an addition X pounds to compress an additional inch.

If we want to take a 100 pound spring and compress it two inches but it's not preloaded, it's going to move 1 inch for the first 100 pounds, then it will take an additional 100 pounds to move it that second inch, so we have a total of 200 pounds.

If we want to take a 100 pounds spring and compress it two inches but it's preloaded 1 inch, it's not going to move at all for the first 100 pounds, then it will take an additional 100 pounds to move it that second inch, so we have a total of 200 pounds. That's why you don't want to add a lot of preload to a spring.

 

Before I delete that spreadsheet I did up another scenario for a typical rear shock coil spring.

Obviously I made some simplifications. E.g. Leverage ratio typically changes through the travel. And a standard shock stroke is 55mm rather than 53.3mm etc. But it gives the idea. (A higher leverage ratio equates to more additional force required, and vice versa).

So I think we see that preload does do more than just control sag. It highly affects the spring "stiffness" up to around the middle of the travel. And it has some effect, reducing, through to the end of its travel, including some effect on bottom out.


PS Typically there's around 60/40 weight distribution rear/front (just glancing at a post above there that introduces sag and rider weight etc.).

 

It doesn't change the "stiffness" because the rate of change is the same.

Think if it this way, each shock is sitting at sag. How much additional force is needed to compress the shock an additional 5mm? 100 pounds for both.

 

One more post on this, because it seems there still remains some misunderstanding.

Have a look at the extra column I added to the chart for additional illustration. Column I.

It indicates the equivalent stiffness unloaded spring at each 10mm of travel for a preloaded spring.

 

One more post on this, because it seems there still remains some misunderstanding.

Have a look at the extra column I added to the chart for additional illustration. Column I.

It indicates the equivalent stiffness unloaded spring at each 10mm of travel for a preloaded spring.

View attachment 2099921

The rate continues to be the same 500lbs/in regardless of preload. The preload is just adjusting sag and ride height. I don't know how else to explain this to you.

 

@ronank You're digging yourself into a bigger hole the more you try to explain your reasoning. Of course a spring gets stiffer as it's compressed but that doesn't change the rate so please just go ride your bike instead of spending all this time on these irrelevant spreadsheets.

 

The guys above are all right. I'll also try to help on it:

It indicates the equivalent stiffness unloaded spring at each 10mm of travel for a preloaded spring.

Yes, and that's irrelevant. All you're showing is that a preloaded spring take more force to compress from 0 to X-mm than a non-preloaded spring. Well, that's what preload is for. Because once you know the rate you need, the preload allows you to set the ride height independently of it. (and that's much better than air in that regard!)

The exercise of figuring out what a non-preloaded spring stiffness would be required to give the same force as a preloaded spring stiffness at the absolute X-mm of travel is a waste of time.

And in this case, the same rider is going to experience a different "stiffness" depending on whether it is preloaded or not.

No, that is a misconception of yours. Forget that idea. He will just experience different ride-height. You need to understand that:
1. The absolute amount of travel (from 0mm!) used for a given obstacle will vary with the preload, yes. (that is, where your travel indicator o-ring will sit on the shock shaft / fork stanchion after the obstacle vs. the total amount of travel on offer... say you used 140mm of travel out of 160mm available on your suspension)
2. The relative amount of travel from ride-height (a.k.a SAG) used on a given obstacle will be the same regardless of preload, and solely dictated by spring-rate. (that is, the amount by which that o-ring moved before and after the obstacle: say from 40mm to 140mm...)

You can add more preload so that the "absolute amount of travel" only reaches 120mm of travel used instead of 140mm (that is, where you o-ring end up)... but that's only because you started from a higher ride-height with only 20mm of SAG instead of 40mm by cranking up the preload. But still used 100mm of travel in both cases and still felt exactly the same thing through your legs/arms.