Digressive or progressive shocks

Digressive or Progressive shocks.


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    7

Metcalf

Expedition Leader
This article does a good job breaking down the difference.

Right, I am saying some of the stuff you have posted is a little bit confusing as far as terminology.
The Accutune article is spot on, they know their stuff. I worked with Ryan on a set of shocks for my last project.
 

Metcalf

Expedition Leader
If your shocks are good and firm. Try some softer springs. Coils are cheap. Not sure if I'd bother with the trucks leaves.

Any in line shock is a huge risk of blowing out. Another thread has Bilsteins blowing out everywhere, and Fox's lasting longer.

An inline shock has a very small airspace for shock rod displacement. You might have 200psi in that shock, but when it compresses, you'll have as much as 800psi! Resi shocks have much larger air chambers, so less pressure build up.
If there isn't a IFP to separate the gas charge from the oil, all the nitrogen gas just emulsifies into the shock oil ( which has a negative effect on valving consistency )
An internal IFP can still work ok as long as there is enough gas volume to work with ( but usually comes at the cost of more shock length for the same travel )
At full extension the IFP in the shock body can have a lower charge pressure to help pressure ramp rate....but because of lower pressure will not keep the oil from emulsifying as much.
 

b dkw1

Observer
OK, lets set a few things strait.

An inline shock has a very small airspace for shock rod displacement. You might have 200psi in that shock, but when it compresses, you'll have as much as 800psi! Resi shocks have much larger air chambers, so less pressure build up.
Pressure ramp up is good to a certain point, it helps fight cavitation. Even on 3.0 Coil overs, I set the air space in the resi pretty low to help combat cavitation.

Shocks with external reservoirs have better cooling,
Correct, a long as your hose volume is less than your shaft displacement. If it is more, a resi has very little effect on oil temps. If you have a recirculating system, it's good for a 100* drop in some apps.

On a small shock with a big shaft this is a larger flow ( 2.0 with a 7/8 shaft as an example ), but as the shock diameter increases the total effect external adjusters can have on overall damping drops quickly.
Shaft size/fluid displacement determens how effective the external adjuster is, nothing else. Body size has no effect.
 

Metcalf

Expedition Leader
Pressure ramp up is good to a certain point, it helps fight cavitation. Even on 3.0 Coil overs, I set the air space in the resi pretty low to help combat cavitation.

Correct, a long as your hose volume is less than your shaft displacement. If it is more, a resi has very little effect on oil temps. If you have a recirculating system, it's good for a 100* drop in some apps.

Shaft size/fluid displacement determens how effective the external adjuster is, nothing else. Body size has no effect.
On a larger diameter shock, the pressure ramp function is going to be less because of the smaller shaft vs body diameter ratio though? Any idea how much pressure ramp you are seeing with the reduction in reservoir gas volume? What starting pressure are you using at full shock extension?

I disagree on the body size having 'no' effect in relation to the external adjuster. The size of the shaft vs body/piston is going should be proportional into how effective the adjuster is going to be. On something like a 2.0 with a rather small piston/flow area, but commonly a larger 7/8 shaft, will be displacing a rather large volume of oil through the reservoir hose. On something like a 3.0 shock, even with a 1" shaft, the fluid displacement through the hose is going to be rather small compared to the flow through the piston. I guess I am saying the external adjuster can only be so effective....more effective on a 2.0 vs a 3.0?
 

b dkw1

Observer
A 1" shaft displaces more fluid than a 7/8" shaft. You will get more damping from it. Being that a 3.0 has way more damping capacity than a 2.0, you will not be needing to use it nearly as much.

N2 pressure depends on the shock an the application. Resi out the top like a coil-over in a race app can run 350 at full extension. Resi out the bottom like a by-pass can run 50# and be happy. as for progression, you need to look up the max PSI ratings for the shaft seals and stay under them.
 
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