OP I forgot to get back to this thread earlier but here is the information I have on the RC4.
I have tried to make detailed yet understandable.
Most important thing is spring rate. You need to make sure you are sitting on 30-35% sag, I personally use the middle chain stay setting and run about 30% works well. At approximately 60kg I use a 250 and maybe going to a 275. Gee atherton on this frame at 80kg used a 350.
You can use the following calculators to check.
http://www.bearandwife.com/bear/cycling/springcalc.html - my personal go to
http://www.tftunedshox.com/info/spring_calculator.aspx - my cross check.
After the spring rate is right its time to get rebound sorted out first.
Rebound- Obvious one this one, the rate at which the suspension rebounds or extends after compression, 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 rebounds 2 then you hit another bump you use another 3 then rebound two you can see using 6inches and rebounding 4 means that the fork is packing down (getting lower). You want a balance.
Too fast and the bike will feel unstable and kicky, basically it is reverse you are using say 4 and the suspension is trying to rebound 6 which is impossible so you end up with suspension kicking the suspension back.
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.
Compression: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. Test high and low settings.
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. basically anything that results in a slow shaft speed compression. Again I always suggest you try a high setting and then a low setting to get a extreme feel of what I am talking about.
Pressure (BV) - The pressure in the shock chamber controls the overall dampening of the shock but can primarily be used to control support in the suspension / mid speed compression. I use about 170. Always stay within the recommended ranges. This basically is the support in the shock.
Bottom out control - BOC controls how much the suspension ramps up towards the end of its travel. or how progressive it it.
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, initial compliance 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. (remember HSC controls initial compliance of a HSC hits.)
If you find you have now set up the bike for the rough but are still bottoming out on big hits and 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 in reality we are not using one of the other but generally a mix of both. 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 due to less velocity and lower shaft speed. More support means more LSC but more bump absorption means less LSC. So there will be some cross over. 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.
LSC also has a minor affect on initial traction but this will be found out during testing.
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 and adjust as you test and tune.
Remember the order
spring rate
rebound
LSC/HSC
pressure
BOC
I hope that all makes sense and helps with the RC4.
DK
and may go to a 275lb.
