Pro rate spring /pro rate rebound?

DEANSFASTWAY

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#1
If you have a progressive rate spring would it be beneficial to set up progressive or position sensitive rebound ? Consider this a pro rate spring stores a xcertain energy coefficient at certain lengths if you compress farther the energy increases at a higher rate curve would you think that the rebound force should rise at the same rate, of couse shaft speeds go up and a 2nd stage stack could be tailored to suit the speeds but thats really speed sensitive but Im thinking like true position sensitive? Any thoughts???
 

jmics19067

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#2
I think it could be possible to get away with a true position sensitive rebound dampening. In my feeble mind the only force the rebound dampening sees is the coiled spring which would be position sensitive.


never mind as I wrote that I realized it woudl only hold true while in the air. If say on rolling whoops and the wheel is following the ground<as it should> you would have to account for the amount of gravity pulling the bike down against the angle of the back side of the whoop. While rider/bike wieght and gravity would be constant the inertia/angle of the downslope would be changing constantly. Whether or not it is significant compared to the energy stored by the spring I wouldn't know.


How is that for a useless post of me arguing with myself :o
 
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#3
You are not looking at the whole picture. What happens within the spring is not as important as what occurs at the rear wheel. Any linkage setup has progression engineered into it by altering the leverage. The shock's position is constantly changed by the linkage to create a force curve relative to the rear wheel travel. In order to mimic this occurence progressive springs are used in the PDS setups. Whilst the lean angle of the shock creates a certain amount of progression, it is inadequate and needs to be supplemented with the spring. The damping is and needs to be velocity sensitive as we are trying to control vertical wheel velocity
Originally posted by jmics19067
I think it could be possible to get away with a true position sensitive rebound dampening. In my feeble mind the only force the rebound dampening sees is the coiled spring which would be position sensitive.


never mind as I wrote that I realized it woudl only hold true while in the air. If say on rolling whoops and the wheel is following the ground<as it should> you would have to account for the amount of gravity pulling the bike down against the angle of the back side of the whoop. While rider/bike wieght and gravity would be constant the inertia/angle of the downslope would be changing constantly. Whether or not it is significant compared to the energy stored by the spring I wouldn't know.


How is that for a useless post of me arguing with myself :o
 

DEANSFASTWAY

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#4
Yeah Terry we know its velocity sens but Im thinking of a position sensitive possibility tailored to the spring rate ramps.
 

jmics19067

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#5
The shock's position is constantly changed by the linkage to create a force curve relative to the rear wheel travel. In order to mimic this occurence progressive springs are used in the PDS setups.

the "rising rate" is position sensitive. the energy stored by the spring would be position sensitive. Although the leverage changes from no travel to full travel the leverage is constant any time the suspension is at half travel also anytime the spring is half collapsed it is storing the same amount of energy.
The only thing that would change is how much weight the wheel sees of the bike and rider due too inertia,terrain down slope and also chain torque now that I think of it.
 
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#6
Even with the PDS system, damping is still velocity sensitive yet with a positional influence. Think about it. If you remove the spring from the shock and raise the rear wheel slowly you will feel little change as you go through the stroke. move it quickly and you may then feel the influence of the needle and the second piston. Hypothetically of course. I understand what you say about the spring force, although variable, at a given point it becomes a constant. But the same can be said for a linear spring. The energy stored in a spring under compression is accumulative and the opposite could be said for its extension. Wether progressive or linear the force is under constant change. The difference with a linkage is that we have leverage creating the progression which once again at a given point is a constant and therefore position sensitive. KTM are trying to manipulate the damping through needle influence at given points. This influence is not always wanted or required. Hence the reason we are still discussing the capabilities of the PDS system.