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Contractive Suspension

Jeremy Wilkey

Owner, MX-Tech
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Jan 28, 2000
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#1
A few weeks ago Mace had a string called challanging authority..
(BTW) MACE your springs have been sent.

The whole spring preload thing really got my gears turning.. Maces basic contention was as follows...

By using a light spring heavly preloaded we negate harsh suspension reactions do to spring loads, while maintiang static ride hts by having a realtively large preload factor. Very similar to car suspension set-up. We talked about all the posiblites multirates etc..
The genral point is that this often causes negative suspenbsion charatcertics in the moments where the suspension is qucikly being loaded and unloaded.. Say breaking bumps..

Ohlins orginally worked on contractive suspension and then FMF's Rob Henderickson (Now RG3) worked with it..

Contractive suspension would have a value in a high preload situation as we could control the topout reaction that a highly preload spring would create. From what I can tell no one had used this concept with relatively light springs. As my company works toward devloping our line of shocks I intend to spend more time on this question, intreg, problem.

Anythoughts..

Regards,
Jer
 
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#2
Contractive suspension basically stays at ride height until acted on by a load, correct? Ty Davis raced with this on his KX 500 a few years ago if my memory serves me correctly.
 

svi

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#3
By contractive do you mean the damping increases rapidly during the low speed phase and then increases less rapidly at higher speed ? The damping and preload combining to support the bike at the required ride height.
 

KiwiBird

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#4
Didn't Suzuki have something like that with a heavily preloaded, light spring and a large top out spring and then adjust the ride height with air?
 

Jeremy Wilkey

Owner, MX-Tech
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#5
I wish I could find the orginal DR article about it...

Basically it serves to allways settle the componets to static length. Coinsider that you average bike really has slop in the top part of the travel. This is good as it aides traction, and bump responce. However when the bike oscilates, or transtions durning power transfers, or braking this action can be undamped.. contractive does just that. I think you could use that to control a higly preloaded springs reaction.

I don't know if anyone has been using it recently or not.. I was not aware of it but many minds are allways working on different things..

The air idea would not acomplish the same thing but another intreting concept.

Regards,
Jer
 
- a d v e r t i s e m e n t -

NVR FNSH

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#6
Jeremy,
I think I have the article you're looking for - I'm a pack-rat. Yes, I cut out the articles I want to keep & put them in sheet protectors in a binder....

I'll try to find the article in the next day or so and send you a copy if you'd like.

brian
 
- a d v e r t i s e m e n t -

MACE

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#7
I think I can find the article as well. It wasn't clear to me at the time what was going on with this concept.

Sounds like a beaching way of lowering a bike though!

Unfortunately, I see no way around adding a fair amount of spring weight.

------------------
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..."
 

svi

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#8
If you had a shock with a large diameter shaft could you then use a combination of gas pressure and preload to provide the extension force required to use a lighter spring as they do in some car shocks or would the linkage ratio negate this.
 
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#9
Is their a way to help the forks handle stutter bumbs? I have the suspention set up great for the rest of the track, it's just those darn bumbs beat the hell out me.
Any suggestions??

------------------
push the bone back in, an ride on
 
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#10
If memory serves me contractive suspension limited the travel to the total travel minus race sag. It basically pulled the suspension down to the level it would be at with the rider aboard. According to Danny Laporte it was very good on natural terrain but it perfomed poorly where you needed to use the suspension rebound to clear SX type obstacles. Seeing that most MX tracks are becoming more SX like I think the idea was behind it's time.

Cameron
 
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#11
i can't see the theoretical advantage of contractive suspension.

if you use a lighter spring with more preload in order to hold up the bike, you will need more compression damping since the spring force will be less than normal in the compressed state.
 

MACE

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#12
Jer, I sent copies of the article. It might be interesting to do a patent search on this one.

In the rear, the execution of the FMF version was either very clever over-complex. I can't quite decide which. They used a hydraulic "buffer" which had an extending piston which pushed on the linkage to hold the rear down to about race sag height. The "buffer" was controlled by what appears to be a remote preload adjustment device off a road racer.

In front it looks like they have on each leg a hydraulic "buffer" up near the clamps which is attached to the axle clamp by a tension cable. It seems that when the front travels past the "contractive" point that the cables just have to buckle out of the way as I see no way to take up the nine inches or so of travel. This seems kind of flaky.

I guess I keep thinking that this could all be done very simply by using overgrown "topout" springs internal to fork and shock.

This seems like a great way to lower suspensions without giving up the good qualities of long travel. In fact, I wonder if much of the improvement claimed is of the same nature as Rich's endorsements of lowered suspensions.