Mountain Biking - SID fork adjustment question

I got a shock air pump and read the manual, then adjusted my SID Race suspension fork today. A few questions, the manual (as usual) was rather unclear:

• The top chamber is for 'positive air pressure'. It appears you pump up BOTH sides of the fork for this.

• The lower chamber is for 'negative pressure'. There is only one Schrader valve for this, the bottom of the fork on the opposite side appears to be a dial control making the rebound faster or slower.

What the F is the relationship between 'positive' and 'negative' pressure?

I set the rebound in the middle. I didn't know what the F they were talking about in that stupid manual.

At any rate, after setting the air pressures to roughly what the manual prescribed, the shock feels GREAT, not sloppy like it did from the factory (it didn't have nearly enough air pressure). Love how it feels now, just want to understand how the relative air pressures work. Also, why do you fill both air chambers on the top of the fork and only one on the lower part of the SID?

I don't know about how 'noodly' this fork is compared to other high line race forks. You guys are the experts here. But compared to my 1999 Manitou Carbon this one feels 5x better. More supple response, better feel in every way. No comparison. Doesn't feel noodly to me, but that's like a hopeless Fred saying he has a great road racing bike. I suppose it depends on what you're used to. For me this SID is a huge improvement.

To put it really simple, the positive chamber "pushes" while the negative chamber "pulls" on the fork travel. So the positive is holding the fork up, while the negative is trying to pull it down. Increasing negative pressure makes the fork more compliant. Increasing positive pressure makes the fork stiffer, and harder to use all the travel. If the negative pressure goes over the positive pressure, you will actually shrink the fork since it is 'pulling' more than it is 'pushing.'
I'm not sure what you are talking about the positive being on both sides. There is no valve on the top of the right leg of a SID. The two chambers (positive and negative) are in the left leg, accessible from the top (positive) and bottom (negative).
Rebound is simply how fast the fork pops back up. It's an individual preference, so just play around with it.

To put it really simple, the positive chamber "pushes" while the negative chamber "pulls" on the fork travel. So the positive is holding the fork up, while the negative is trying to pull it down. Increasing negative pressure makes the fork more compliant. Increasing positive pressure makes the fork stiffer, and harder to use all the travel. If the negative pressure goes over the positive pressure, you will actually shrink the fork since it is 'pulling' more than it is 'pushing.'
I'm not sure what you are talking about the positive being on both sides. There is no valve on the top of the right leg of a SID. The two chambers (positive and negative) are in the left leg, accessible from the top (positive) and bottom (negative).
Rebound is simply how fast the fork pops back up. It's an individual preference, so just play around with it.

On my SID Race on top, there is a Schrader Valve on each side, I was able to pump each side up and get an air pressure reading off both. That alone made me not trust the manual after that, it completely flies in the face of what the stupid book tells you. Go figure. That's right, on the top of the SID Race, TWO valves, one on either side. On the bottom, only one valve. By the way, what's 'right' and 'left' on an MTB suspension fork? Right/Left as I stand facing the bike or as I stand over the top tube as if I'm about to ride the bike??

Thanks by the way, very lucid explanation. Maybe you should write the manual for the Idiots @ Rock Shox. Good grief, who writes this crap for these guys? Are they trying to confuse the new owners even more? They are succeeding. Somebody tell SRAM. The little booklet that came with the SID would make nice fire kindling of course.

I'm talking as you stand over the bike.

The right side air chamber is the PURE chamber (IFP chamber I think is the name for it). Just don't let it get below 20psi, it will mess with the damper and you'll loose travel. Other than that, I really don't know what to set it at. Play around with it and see what it does.

I'm talking as you stand over the bike.

The right side air chamber is the PURE chamber (IFP chamber I think is the name for it). Just don't let it get below 20psi, it will mess with the damper and you'll loose travel. Other than that, I really don't know what to set it at. Play around with it and see what it does.

'Stand over the bike' doesn't tell me what you mean...Facing the bike looking at the head tube badge? Or the other way around (looking over the handlebars the way you do when you ride the bike)?

What the F is a 'PURE' chamber? What's an IFP chamber?

You would think something this simple couldn't possibly be made this confusing, yet they have achieved it. That's something. If the world was good at making **** easy, Apple Computer wouldn't make all the money they do. Thank God for the Microsoft Effect.

You would think something this simple couldn't possibly be made this confusing, yet they have achieved it. That's something. If the world was good at making **** easy, Apple Computer wouldn't make all the money they do. Thank God for the Microsoft Effect.

Simplicity or adjustability, you can't (usually) have both.

It's the damper. It keeps the fork from being a pogo stick, basically. Just leave it at, say, 80psi and be done with it.

Standing over the bike, like you were riding it. The side with two air chambers is the left side.

Thanks Z. Very helpful. What I'll never figure out is why they couldn't include a manual that laid this all out like you guys did.

Haha, well, I don't think most newbies have Sid forks...

http://www.sram.com/en/service/rockshox/view.php?catID=1&subcatID=9

most fork manuals suck. ride with the shock pump a bit, play with your settings to really get things dialed in.

What the F is a 'PURE' chamber? What's an IFP chamber?



The Pure Delite damper is a primitive form of low speed compression damping. The working pressure is 20-60 psi. More pressure = more low speed compression damping. Once you get the dual air side set right for your weight and riding style, adjust the Pure chamber pressure to eliminate peddaling bob. But, the higher the pressure, the more small bump compliance you'll lose.

IFP means Internal Floating Piston. This piston seperates the rebound damper oil from the Pure chamber air pressure.

The SID race that he has (and that I have) has positive on both sides. Most of their other forks do not (from what I gather). The manual does not refer to the SID race as having it on both sides.

It has a negative on one side bottom and then a twisty thing on the other.

So, the right side (from the perspective of the rider) is the pure/IFP thing?

Thanks

That SID product manual is brutal. Many are. If I'm a newbie, that's what the stupid manuals are supposed to be for. How these companies can put out this crappy literature is beyond me. The PowerTap book was also lame, but in their defense, that product is far more complex. I was able to mostly figure out the PT from that book.

So, the right side (from the perspective of the rider) is the pure/IFP thing?



Yep, adding air to the right leg controls low speed compression damping.

I must confess I was amazed how easy it was to adjust the fork and how different it felt afterwards. Now it feels fantastic. So that's really the bottom line.

The Pure Delite damper is a primitive form of low speed compression damping. The working pressure is 20-60 psi. More pressure = more low speed compression damping. Once you get the dual air side set right for your weight and riding style, adjust the Pure chamber pressure to eliminate peddaling bob. But, the higher the pressure, the more small bump compliance you'll lose.

IFP means Internal Floating Piston. This piston seperates the rebound damper oil from the Pure chamber air pressure.

OK, I was sticking 120 psi into both top schraders. This explains why I didn't care for the ride over washboard stuff much. I was jacking the low speed compression damping through the roof and I had very little rebound damping to match. I didn't have a problem with pedal bob, but I guess that should have come as any sort of surprise.

The manual is a complete POS. I have build more than 1000 shocks over the last 10 years or so. Ohlins, Penske, Dynamic, Fox, Sachs, etc. I know WTF I'm doing when it comes to putting these together and tuning them. Having said that, I was way off and that was _after_ reading the manual. They need to pull their collective heads out of their crack.