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position sensitive shocks


Active Member
Hey everyone,

I am interested in learning more about position sensitive shocks. Not bypass shocks but rather interal position sensitive shocks.

How they were explained to me is the are a smooth body shocks that have holes at various stages of the stroke in the body. There is a sleave that goes over everything that is held in place. During the shock stroke the nitro and oil mixes and gives different dampering.

I am looking at these because of the of space issues. If anyone has any info that they could fill me in with that would be great. Thanks in advance.


Well-Known Member
Not sure what you're talk about but if you mean something like an emulsion shock I think they're generally not used for dezert racing, because if the piston moves up and down too much/ too fast the shock oil will foam.


Active Member
Yeah search works wonders thanks for the help guys. Go Go gadget nice to see you on here as well as DR


Active Member
Hey thanks for all the help so far. Alot of what im seeing is shocks with coilovers that are adjustable. Im looking for something that looks like your standard emoulsion shock, that has interal bypasses or the sleave idea. The other idea was just to run a smoothie next to my coil over and just add alot of rebound to it?

baja stu

Well-Known Member
I heard that the drawbacks of those shocks are that you haft to tear them apart to adjust them. And for the price I would just buy a 2-tube 2" bypass. It's cheeper.


Well-Known Member
I've recently been reading up on different styles of internally position sensitive shocks so I thought I'd bump this thread and dump the info here.

One style is a tube inside the outer shock body. The piston rides in this inner tube and the inner tube has bypass holes and/or reed valves to allow more flow the more extended the shock is, in the case of the reed valves in the compression direction only. I have read that one downside of this design is that most of the heat is generated in the inner tube, there's not much flow in between the tubes, and they run hot.


Another design is sleeving just the top few inches of the shock body and having a second piston. The second piston is on the same shaft as the main piston and smaller in diameter. It can be set up with the same shims as the main piston for tuning. We've modified shocks in this manner by just using a brass piston and no wear band since it's only used a small percentage of the time.

shock 12 PS.jpg

Fox sells this as "bottom out control" (BOC). AFAIK it's not really meant to be tuned (but probably could be) and only provides increased damping in compression (but could be modified to add damping in rebound). As you can see the Fox design is progressive.




There is also a needle design used by a few manufacturers. A needle hangs from the top center of the shock and blocks off a hole in the shock shaft in the last few inches of travel to increase damping. A simple version of this is used by Walker Evans and basically just adds bleed for most of the travel. Needle not shown.




There is a good video of how the King needle shocks work, it's more complicated but more tuneable and doesn't add a lot of bleed.

I would be interested to see any other designs out there.