[ktm520]

The reason is that both the firm and medium spring will be fully compressed at full stroke, so the final force for those two curves has to be the same.

Have you tested the spring rate or is this speculation? I assume Manitou doesn't publish the spring rates. I've got a Tower Pro on the way so I'm reading up on the Mars setup.

 

[solitone]

^^

No no, it was just speculation. As I said, I'd like to have real spring curves, but unfortunately I don't have any for Firm and Medium coil springs.

As far as I know, the only available spring curves currently available are the following, which refer to the XX-Firm (AKA Clydesdale) coil, though. These curves where provided to TrailMaker by Manitou's chief engineer Ed Kwaterski, and he published them in the interesting doc referenced by shiggy.

 

[ktm520]

Ya, I read TrailMaker's article. Although the absolute numbers in that chart don't apply to softer springs, it gives a very clear picture of what part of the curve the different variables affect. As far as spring rate goes, it's not that hard to measure. I like having curves to look at, but I doubt I will go down that road with this fork unless I have issues.

If you haven't already done so, I strongly urge you to experiment with the low speed rebound setting. It seems to be the most widely overlooked aspect of suspension setup and can make or break the action.

I'm curious to hear if anyone has played with revalving the high speed rebound.

 

[solitone]

Ya, I read TrailMaker's article. Although the absolute numbers in that chart don't apply to softer springs, it gives a very clear picture of what part of the curve the different variables affect.

Yes, but the thing those graphs don't tell you is where (i.e. at which point in travel) the curve for softer coil + higher pressure becomes greater than that for stronger coil + lower pressure.

 

[solitone]

I don't know where you got those curves from, but they're probably wrong. The reason is that both the firm and medium spring will be fully compressed at full stroke, so the final force for those two curves has to be the same.

You're perfectly right. Those curves where just sketches I drawed, and I was wrong. As you said, final force has to be the same with both coils.

On my medium spring for a 100mm minute pro, it takes maybe about 100 lbs to fully compress that spring.

How do you know that? Do you know what force is needed to fully compress a firm spring?

I'll do the test you suggested, as well as measuring sag again--hopefully getting more precise measurements.

Cheers

 

[beanbag]

I measured my spring by holding a flat plate over the top and then putting most of my weight into it.

That chart you have shows the spring curves for your firm coil. I dunno about your coil, but mine for a 100mm fork can compress by less than 2" before it bottoms out (e.g. the blue plastic push rod hits the metal compression rod).
Next time you have your spring out, you can see how much yours compresses and get the force value from the chart.

There is something weird about the manitou chart in that the 90 psi black curve starts to diverge from the spring at below 50 lbs. That is odd.

 

[beanbag]

Yes, but the thing those graphs don't tell you is where (i.e. at which point in travel) the curve for softer coil + higher pressure becomes greater than that for stronger coil + lower pressure.

All you need is to measure the height / volume of your air chamber, and then you can calculate these curves out yourself.

 

[solitone]

There is something weird about the manitou chart in that the 90 psi black curve starts to diverge from the spring at below 50 lbs. That is odd.

Yes, because the air piston should begin move at about 100 lbs

 

[solitone]

Try this: Pump up your shock to the usual pressure, and leave the shock pump hooked up. Sit on the bike so that the fork sags. If the air pressure increases, that means that the air piston is already moving just from the sag. If this is the case, then that also means that you can keep the same sag if you go with a softer spring and use more air pressure. Then the air piston will take over during a later part of the stroke.

I've measured how much the fork needs to compress so that the air piston starts moving. As usual, it's difficult to have accurate measurements, next time I'd better ask a friend to help me.

Here are the results. I also noted sag figures where available, but I need to measure sag again to have more accuracy:

• 70 psi: air piston moves at 8 mm (sag 28 mm)
• 80 psi: air piston moves at 11 mm (sag 12 mm)
• 85 psi: air piston moves at 15 mm (sag 11 mm)
• 90 psi: air piston moves at 17 mm (sag 11 mm)
• 100 psi: sag 12 mm

As you see, only with 70
and (perhaps) 80 psi the piston moves from the sag. With 85+ psi the piston moves later in travel, therefore sag depends only on the coil spring rate. This explains why sag doesn't change increasing air pressure from 85 to 90 psi.

 

[beanbag]

I did the same test on my fork and the piston also moves before I think it is supposed to. I think there must be a trapped air space somewhere, or some kind of rubber bumper or o-ring under the piston that allows it to move around. I never had the air piston out so I wouldn't know.

In any case, I made some plots for MY fork. I guessed on the spring rates. Also, the final force came out to be a little too low so I am missing various air pockets trapped in other parts of the fork.



In any case, I used to have a medium spring but now I run a soft spring. It ends up giving a smoother and more linear curve.

 

[solitone]

I did the same test on my fork and the piston also moves before I think it is supposed to.

Do you refer to my piston, or to what is shown on Manitou's plots?

I don't know whether or not my piston moves before it is supposed to.

--EDIT--

BTW, why the force of the MARS spring at full travel (100 mm) is lower then the force of the air spring alone, in your plots?

We said the coil spring is fully compressed at that travel, so the force of the MARS spring should only depend on the air spring.

 

[beanbag]

u add the dotted plots horizontally to get the total travel

 

[solitone]

I'm afraid I don't get it. In your graph, the red and blue continuous lines (MARS spring) peak to 170 lbs at 4 inch displacement (100 mm). In contrast, the green dotted line (air spring) is much higher at 4 inches, although it's not shown.

 

[beanbag]

you don't actually end up compressing the air chamber 4 inches. it compresses 2 inches and the spring compresses 2 inches and thus the fork compresses 4 inches. You are supposed to read this graph like it is sideways, i.e. you pick a force value first and then read off the displacements.

 

[solitone]

OK.

I measured the air piston movement again, and I confirm that 80 psi are enough to reach the point where the piston moves at a displacement equal to sag. More than 80 psi, and the piston moves at a displacement greater than sag.

So, for pressures >= 80 psi, sag is given only by the coil spring, and it is 11-12 mm--too little, because the firm coil is too hard for my weight.

 

[mullen119]

A lot of great info in this thread on how to tune the Mars spring system. Either beanbag or Solitone should make a guide with the tips and tricks to make sure you have the correct coil spring for your weight and what not. The spring system is complex enough that a lot of people have problems setting it up, and a guide on here would help a lot of people.

 

[solitone]

Sure! As soon as I complete my tests I'll wrap up all information in a how to guide.

I've just ordered a Medium Ride Kit and soon I'll be able to try the new setup.

 

[solitone]

some more videos

This evening i shot some more videos.

Here is the test with 90 psi, that last time I didn't manage to record:

 

[solitone]

new vid 85 psi

And, as a comparison, here a new recording with 85 psi, that last time was really poor quality:

All other settings are the same: firm coil, LSC damping MAX-5, HSC stock trail shim stack, rebound damping MAX-3/4.

Please comment!

 

[solitone]

85 psi on a different path

And a longer descent on another path, which should allow to check the fork's behaviour on different conditions (fork inflated with 85 psi of air).

Here there are no steep sections, but the surface is generally rougher, with many boulders.

As in previous vids, there's a pretty amount of mud because of the heavy showers we have been experiencing in the last weeks here. So the camera lens isn't always clean.. Sorry for that!