The blue adjustment in the end if bottom out control not boost valve.
Boost valve is the pressure in the chamber.
The BV pressure offers over all support for the shock and on the rc4 can be used primarily as mid stroke support and ending stroke support.
The BOC changes the progressiveness of the shock towards the end of its stroke. The BOC is the last adjustment.
By adding BOC you are decreeing the chamber size so the pressure builds up quicker preside will change the over all feel where more BOC will be more prelevant towards the end during ramp up.
I'll try find my previous post in a thread about the shock and post it here.Give me a few minute.
Basically LSC is low speed shaft movements and HSC is highspeed shaft movements (this does not mean the bike speed although this will have affect as I will elaborate on later)
HSC - this controls virtually all the bumps and rock gardens you encounter, it controls the harshness felt initially or the initial compliance in the shock to forces and over all travel use in rock gardens and rough terrain. I.e you want the suspension to use appropriate travel, if a bump requires 3inches you want to use 3inches no more no less.
LSC - This controls the body movement and momentum shift on the trail so under pedaling LSC can be used to control bob, Under braking LSC can be used to control dive. Set this up to avoid too much dive or travel use under body movement like smooth corners and pedaling/dive. This is also used in wallowing holes.
Rebound- Obvious one this one, the rate at which the bike rebounds, if you have too much rebound dampening (too slow) the bike will pack down, this means that the suspension wont recover enough from a previous hit before it hits another one which means the suspension continues to get lower and lower in its travel. Not enough dampening (too fast) the bike doesn't settle in its travel and you loose traction and you get a harsh or unstable ride.
A good way to understand packing is if you use 3 inches then it rebound 2 then you hit another bump you use another 3 then rebound two. as you can see using 6 and rebounding 4 means that the fork is packing down (getting lower). You want a balance.
some people run very soft suspension and use faster rebound to account for the excess use, while others like my self use a stiff set up and use slower rebound.I prefer the stiff set up, It results in a bike that skimps over holes rather than falling in them, it also helps keep geometry stable.
Bottom out control - BOC controls how much the suspension ramps up towards the end of its travel.
Pressure - the pressure in the shock chamber controls the overall dampening of the shock but can primarily be used to control support in the suspension. I use about 170. Always stay within the recommended ranges.
brief explanation of pressure and BOC use.
Lets assume you have the right spring rate and set the HSC and LSC and rebound up correctly as these are the simple ones.
If you find our are using too much travel in the rough you need to up your HSC, however if upping the HSC makes the bike harsh on square edge hits or in the rough, instead try upping the Pressure. By upping the pressure you are placing more support in the shock and you should notice that you use less travel but the bike is not harsh as HSC is kept the same.
If you find you are still bottoming out on big hits but again changing HSC or upping pressure makes the ride too harsh or too stiff, this is where you use the BOC, this will make the ending stroke of the shock ramp up more.
Now if the following is confusing or you cannot grasp the idea than disregard it and just go on everything else in the post.
Now there is some cross over with HSC and LSC depending on your riding speed. The faster you are the harder you hit things the more velocity is put through the suspension. This becomes a issue as slow riders will be relying more so on LSC than HSC, as you become faster more bumps become HSC and less become LSC, so for a slow rider who is trying to control support and bump absorption it becomes difficult as slower riders, more bumps are LSC. More support means more LSC but more bump absorption means less LSC. So there will be some cross over. The the faster the rider the less cross over there is. So being a fast rider actually makes suspension set up and performance easier.
Ie. slow riders 50% is HSC 50% is LSC. now you are trying to control 50% of bumps with LSC and your also trying to control momentum and movement with LSC so this means the LSC is stretched between two things with more compromise. As you get faster more bumps become HSC so the faster you go you might end up with bumps being controlled by 80%HSC and 20% LSC, this means that the LSC can be focused on its job rather than bump absorption, hence less compromise.
I hope that helps.
Now the information I received in regards to my set up on the commencal is as follows. note: this is assuming you have the right spring rate.
Air pressure, start with 150, run higher pressure for more support / mid-speed compression and to increase the end stroke control. For HSC, start mid range, negative 6 clicks. For LSC, negative 6 to 8 clicks. For rebound, start with the adjuster negative 6 to 8 clicks.
When it says negative, you need to turn the adjusters to full on or full positive and count backwards clicks. As for BOC this is dependent on the bike, start with BOC zero (-4) and adjust as you test and tune.
