[climbingbubba]

Yes I know, Shock set up seems to be the hot topic right now. I have read them though and have specific questions and Ridemonkey seems to be the place all the smart suspension people hide...

This question is aimed at shocks that have adjustable Bottom out knobs and air chambers. Shocks like the Fox RC4, DHX, DSP deuler, Revox, etc

I understand the basic mechanics of it. You add a certain amount of air and when you crank the knob it makes the chamber smaller which will add more BO resistance.

So my question is. What is the difference (in feel) if you run 120 psi with the BO knob cranked in all the way VS running it with 180 psi and the BO know wide open? Is there a difference? will one make the shock more progressive? Im just trying to get an idea on when its better to add air VS crank the knob in.

Ok thats the main part

Bonus Question

I have a banshee legend with a RC4 and will soon be testing a DSP Dueler. The legend is a fairly linear bike and I have been bottoming out the RC4 on rather small drops to flat (under 3 feet). What would be the ideal way to set up the bike using the bottom out knob, bottom out air pressure, and HSC to make the bike more progressive in general? this includes the mid stroke as well. This goes along with the first question nicely but adds HSC to the mix.

Thanks in advance

 

[Udi]

Interesting question, especially since I've been tuning around the same area currently (and ride a Sunday which has virtually the same leverage ratio curve as the Legend).

First thing - the bottom out adjuster and chamber pressure on an RC4 (along with the DHX, Revox, 5th, etc) work very differently to say a Dueler.

The RC4 uses its boost valve (a curnutt style valve) to generate an increase in compression damping that correlates with increases in pressure. So increasing chamber pressure increases compression damping throughout the stroke, and decreasing the chamber size will increase the progression of this damping.

On top of this you will generate a little air-spring preload (by virtue of the air pressure acting on the shaft cutaway surface area), and a little spring rate (not damping) progression. Smaller chamber will mean more overall spring rate progression in this case too, but these spring rate differences will be fairly small.

The damping increase will not happen on a shock without a curnutt valve, so increasing chamber pressure on the Dueler (for example) will just do what's mentioned in the paragraph above. IMO that's not much use on frames like the Legend and Sunday, which really depend on (and shine with) the use of a shock with position-sensitive compression damping.

Bottom line - the RC4 should be a winner in that frame. If you post your weight and spring rate, I'm sure people will be able to chime in with suggestions. I would suggest bottom out adjuster fully closed, and 150psi in the chamber as a starting point.

 

[climbingbubba]

Thanks for the response

Right now I weigh about 190 lbs without gear. I have a #350 coil on it at the moment but only get about 30% sag at most.

I will be reviewing the DSP deuler for a small review site and also general testing for durability for DSP. I ordered a #300 spring for it since I am losing weight pretty fast and I was already over sprung.

I guess i hadn't realized that there was a difference in the dueler and the other shocks. thanks for the heads up