My questions to all the readers(not jer :) )

marcusgunby

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#1
Ive been looking at different suspension principals recently and we can use 2 ways of working.
1 Light springs/heavy damping/with possible high oil heights(forks only)
2 heavy springs/light damping
Which one is better for different applications and why?
Also with a low flow pistons you have the piston its-self acting as high speed damping so you can have a sensitive shim stack for LSC.
If we have a high flow piston with a 3 stage stack would this not achieve the same thing-isnt this what the 3 stage stack was designed to do?Did WP use the 3 stage stack first-ive heard they did, is this true?
Why do most mx shocks have 2 stage stacks and forks single stage?
No you dont win prizes for these q'S :(

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Jeremy Wilkey

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#2
Marcus,
ARE YOU SURE I CAN'T ANSWER THIS ONE PLEASE, PLEASE PLEASE..

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KNOW IT ALL KID IN GRADESCHOOL MODE OFF...ACTUALLY.. :EEK:
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#3
hi marcus, i'm learning .
let me have a go at this.

1)suitable for high speed damping(with LSC)
sq-edge bump

2)I feel it will have pogo stick effect since the low damping wouldn't be able to hold the stiffer spring spring back force

If i'm not remember wrongly, WP did use a 3-stage valving stack. But I don't really understand why they are using a 3-stage, a dual stage should be enough for most application.

mx fork with single stage valve maybe is because they are riding over and over in a same track with slight changing terrain. trail bike will have dual stage valving to accomodate different terrain.
mx shock with 2 stage, maybe to absord normal landing from jump or high speed damping from sq-edge bump.

just try my best, please give me your comments, thanks =o)

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#4
As far as spring rate vs damping:
Shim stacks are speed sensitive and springs are position sensitive. If you have too heavy of a spring the shock would probably want to deflect more in high speed situations where the shock didn't have a chance to "reload" for the next bump.

Too light would cause you to have to valve very stiff to keep the shock up in the stroke. That would cause low speed deflection and make getting the high speed correct a lot more difficult.

Piston oriface size:
Race tech's concept is to run very large piston oriface's and stiff valving to compensate. GP racing's concept is just the opposite.
I'll elect think about this one for now since I've erased my comments about 5 times now. We are going to be doing some testing of the GP setup, so I'll try to post back my opinions later.

Single vs Dual (& triple) stage fork stacks:
For the most part single stage stacks are better for supercross where there is very little "chatter" type bumps and a lot of huge hits. For the most part we run 2 stage stacks for outdoor and hare scramble applications. I have a 3 stage in my 98 CR125 and its pretty darn good for oudoors. The 3 stage stack makes the forks feel really linear through the travel but they have a bit of a hard time on the huge hits.

I can't figure out why all of the japanese bikes come with single stage fork setups. My best guess is that they have software for a single stage stack so thats where they leave it. Also you use less shims so that could be a cost savings (engineers vs accountants)

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#5
1)good for supercross. Firm, but compliant because of the light springs. Still has bottoming resistance because of the stiff valving and the high oil
2)Good for woods? Because springs resist bottoming fairly well, but the light valving makes them extremely compliant over small, square edged bumps.

That is all I can answer. Why can't jer answer? He will tell us the truth.

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Farmer John

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#6
1) I do not know
2) Fairly common in the desert. Springs hold the bike up. Light valving seems to not "go away" as much as the heavier valving

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#7
The question is flawed :)

No one would ever want #2 in the shock. It never works. Lighter spring rates will always be plusher! Springs don't prevent bottoming either.

Maybe a relatively higher rate in the front, but only a tiny bit. Preload works better with the right valving anyway.

The small orifice pistons have a limited upper speed limit before they "lock up". A three stage stack can, in theory, have "limitless" speed applicability.

I thought most bikes came with two stage fork stacks. What am I missing here?

PEte
c3hammer@verts.com




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marcusgunby

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#8
kawa125 if jer told us the answers it isnt as much fun and you learn the best by thinking the problem through step by step learning the concepts behind the problems :).I hope i havnt given the impression i have all the answers to the q's as i dont but im interested in others thoughts/experiences.
Ive seen single stage setups for supercross and i believe this gives untimate control for those landings.The 3 stage set ups would in thoery give the sensitivity for woods type riding i would think but im thinking it could work in a UK MX application as well.A 2 stage set up is a good comprimise for the shock and i dont understand why it isnt used in the forks more(ive mainly worked on CR/KTM set ups so thats what i know most about-very little of RM/YZ/KX)
The heavy damping/light spring set up is used by some very fast KTMs(guess who)and ive seen it on the track and it worked extremely well but i cant understand how a 175lb rider could use 0.36 springs even with a twinchamber type fork.
I used to think a stiff spring light damping set up was the way to go as i thought the result would be a plush set up but now im not so sure-after riding such a set up i beleive the spring isnt enough if the damping cant slow it down so you get big bottoming.

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JTT

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#9
Since we're all taking shots here, what the heck....here goes my theory...

A spring is intended to store the energy of a bump and delay the release of this energy over a period of time. Imagine hitting a bump with a rigid frame, there is no delay, the energy is directly transferred to the seat. Preload provides ride height and supports the vehicle and rider.

We are concerned with the rate of acceleration of the wheel as it is deflected by the bump. This rate is determined by angle of the bump face, height of bump and speed of the vehicle.

The spring rate must be enough to absorb the energy of the bump, energy of wheel inertia and sufficiently delay the period of time for the energy to returned. If it is too stiff, too much of the energy will be transferred to the bike (and rider) too quickly (see: hardtail) . If it is too light, the acceleration of the wheel upward will create more energy than the spring can handle and the wheel will deflect too far (causing it to leave the ground).

Using excessive damping to in an attempt to control this is not the way to go leading to a slow moving suspension incapable of handling smaller sharp edged bumps.

My head hurts now...time for some mindless activity...maybe some real work :D



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HiG4s

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#10
I don't know what the damping was set at but a I read KTM had decent results experimenting with high oil levels, 35psi pre-load, and NO fork springs. Per their web site the springs only affect the first 1/3 of fork travel after that it is the oil level/air pressure that takes over.

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MACE

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#11
JTT you are preaching the gospel of Carroll Smith in the context of race cars. I lean towards this philosophy for offroad but I think it must be modified somewhat to apply to big air MX.

Originally posted by HiG4s:
I read KTM had decent results experimenting with high oil levels, 35psi pre-load, and NO fork springs.
Yeah Baby! Let's ditch them springs. I'm quite concerned about stiction and durability though. I think forks actually work better with a very mild fluid leak*. If that happens on your air fork, you'll be rubbin knobs on the fender all the way back home. (Ok if home is 100yds away, not Ok if home is 50 miles away....)

*trademark inflammatory comment

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MACE

One night I was layin' down,
I heard mama 'n papa talkin'
I heard papa tell mama, "you let that boy MOTO,
it's in him, and it got to come out..."
 

HiG4s

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#12
Well, obviously there must have been some draw backs to running with no springs or they would sell them that way, but you have to admit it is an interesting concept.

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MACE

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#13
Originally posted by HiG4s:
Well, obviously there must have been some draw backs to running with no springs or they would sell them that way, but you have to admit it is an interesting concept.
In deed! I often try to think about what parts of the bike are too heavy for their task and I think the springs are prime examples. Have you ever considered that one .94 kg/mm spring will weigh a lot less than two .47s? How about we run one spring? Maybe the off side is set up with positive air pressure for sort of a compromise solution. We currently have pretty good systems, but I doubt we have the ultimate solutions.
 

JTT

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#14
Originally posted by MACE:
JTT you are preaching the gospel of Carroll Smith in the context of race cars. I lean towards this philosophy for offroad but I think it must be modified somewhat to apply to big air MX.
Actually Mace, this theory is from a Motorcycle chassis design book...but the author elludes at this time...

I do understand what you are saying about big air MX of SX, but the same principals apply...I think?...If you take this principal to the higher levels, you will see that there is NO "right" spring for all occassions or even two individual bumps. This means that we are always making a compromise. For SX, your right, the compromise would be towards controlling big air landings, but that just means you are compromising performance in an other area.

On the air side...air is difficult to control due to expansion with heat as well. You mentioned in an earlier post about high pressure nitrogen (different thread). Apparently the Ducatis Corse team (WSB) are using an Ohlins fork with precisely that set up this year...very trick!


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JTT
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MACE

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#15
Originally posted by JTT:
Actually Mace, this theory is from a Motorcycle chassis design book...but the author elludes at this time...
Tony Foale?

On the air side...air is difficult to control due to expansion with heat as well
Air and nitrogen should react very similarly. I would be interested in knowing what amount of heat delta we would see in an air fork. Keep in mind that the temperatures used in the ideal gas laws are in degrees kelvin. There would be some increase in spring rate with heat for sure (there is NOW) but we'd have to do some numbers to know if it is significant. Top level racers will use fork heaters before motos (what a PITA).

Hey I'm ragdolling wildly off topic&gt;&gt;&gt; ;)



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MACE

One night I was layin' down,
I heard mama 'n papa talkin'
I heard papa tell mama, "you let that boy MOTO,
it's in him, and it got to come out..."