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Old 03-19-05, 10:47 PM   #1
rbm
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Adjusting Elastomer shock damping

Hi,

I own a tadpole recumbent trike with an articulated rear arm. The rear arm is suspended from the frame using a shock of an elastomer type. Damping characteristics are determined, I suspect, by the type of elastomer used, the number of elastomer disks stacked in the shock and the preset tightening of the bolt running through the shock, frame and articulated arm.

The damping is too firm at the moment and I'd like to soften it a bit. What is my best strategy? Should I remove elastomer disks, reducing the shock height, or replace all the disks with softer material? TIA.

- Rob
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Old 03-19-05, 11:10 PM   #2
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It sounds like you need a lighter spring rate. So the fix is to use a lighter elastomer. There can be some change made by preload( How much the elastomer is compressed before you put your weight on it) But your ride may not have that or you may have reduced it already. I would contact the trike builder and ask them about your options.
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Old 03-20-05, 12:24 AM   #3
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This is another place where imprecise language is going to get us confused.

The elastomer is actually a spring and it doesn't have any dampening. Dampening is like the shock absorbers on a car. What they do is smoothen out the rate of compression and rebound and greatly improve the ride and handling characteristics. When people say that their bike has a shock fork, what they really mean is that it has a suspension fork. It may or may not have dampening. The good suspension forks have elaborate dampening controls, most have none at all.
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Old 03-20-05, 12:42 AM   #4
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Elastomers have a property that dampens a little bit, but IMO elastomers suck. Maybe you could find a good short stroke coil over or air shock.
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Old 03-20-05, 05:43 AM   #5
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Originally Posted by Dirtbike
Elastomers have a property that dampens a little bit, but IMO elastomers suck. Maybe you could find a good short stroke coil over or air shock.
You are correct; elastomers suck. However, the design of the articulation does not allow for a coil or air shock to be installed. There are no arms mounted 90 degrees to the frame and rear arm into which I can place such a shock. The articulated arm is held to the frame by the bolt of the elastomer shock and road shocks force the parts to move relative to each other along the bolt axis, compressing the elastomer material. If I were to draw a rough analogy, the articulation design works more like the action of a pair of circlip pliers (separating as you apply pressure) than a pair of needle-nose pliers (closing as you apply pressure).
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Old 03-20-05, 05:51 AM   #6
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Originally Posted by Rev.Chuck
It sounds like you need a lighter spring rate. So the fix is to use a lighter elastomer. There can be some change made by preload( How much the elastomer is compressed before you put your weight on it) But your ride may not have that or you may have reduced it already. I would contact the trike builder and ask them about your options.
I haven't made any adjustments or changes to the elastomer shock preload as it was set at the factory. So the preload is the value set by the builder and is probably a standard torque value setting, having no relationship to my body weight or riding conditions (I hope my terminology is correct this time). I can't contact the builder, unfortunately, because he no longer builds trikes and doesn't respond to the last email address I have for him.
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