Rear shock compression adjust question

ross_mcculloch

I'm setting up a rear-shock (Marzocchi Roco 3PL) for the first time today. I've used a shock pump to get the correct pressure and I've been told to take the bike off a kerb to get a feel for the rebound adjust.

What I'm stuck on is the compression adjust, as the Marzocchi manual is useless. It's a knob which moves from '+' to '-' through 180 degrees.

- What exactly does it do?

- How do I setup the compression?

Any help greatly appreciated!

stumpyjon

Compression damping works in the same way as rebound damping and controls the speed of the fork movement through the compression stroke. Basically if you back the compression adjustment right off the fork will dive very quickly through it's travel on big hit and you'l go over the bars due to the unexpected speed of the compression. At the opposite end of the scale with the compression damping right up the fork will feel like it's hardly moving as it compresses more slowly. Same principles apply to the rear shock.

How you set it up is personal preference, if you ride a lot of XC you may want to back the compression damping off to get the benefit of the shock over small bumps, if you ride a lot of drops you may want more compression damping set higher to control the stroke.

The advice about riding off the curb is good, best way to learn is to play with the setting to feel what it is doing.

ross_mcculloch

so for general xc riding I'd want it all set up fairly tight with the rear shock not travelling far and rebounding quickly, whereas for bigger jumps I'd want it to travel further and rebound more slowly?

stumpyjon

Other way around, light touch compression damping for XC otherwise by the time the shock had reacted to little hits you'd have already cleared them and it would feel like it was effectively locked out.

dave_hill

ross_mcculloch wrote:

so for general xc riding I'd want it all set up fairly tight with the rear shock not travelling far and rebounding quickly, whereas for bigger jumps I'd want it to travel further and rebound more slowly?

Ermmm... not exactly....

Getting compression and rebound set up to your liking can take time and a lot of experimenting. It may also need changing for the type of riding which you're doing and how you do it.

Unfortunately, there's no firm answer for the question(s), "how much sag/compression damping/rebound damping is correct?" It is all down to personal preference and feel.

Basically the sequence should be this -

1. Set up sag. This is the amount by which the shock compresses when the bike is at rest, with you sitting on it in your normal riding gear in the "attack" position. A good starting point is about 25% of the total shock travel.

2. Set up compression damping. Basically, you need to set the shock so that a) it doesn't blow through it's travel if you look at it funny (too little compression damping) but b) it doesn't need a 20 foot huck to get it moving (too much compression damping). With a basic shock such as the 3PL this is very much a compromise - with more upmarket shocks and forks you may be able to adjust high- and low-speed compression damping separately. This means that you can set up the way that the shock reacts to small hits (such as trail buzz) and big hits (such as large drops) independently of each other.

3. Finally, set up rebound damping. Again, it's a balancing act. Too little rebound damping and the shock will extend suddenly after each hit, pinging you around like a pinball machine. Too much damping and the shock will pack down after repeated hits.

As I've said, it's a balancing act and getting it right can take a lot of time and experimentation. The best solution is to find a short loop and ride round it repeatedly, adjusting one thing at a time, makiing a mental note of how the feel of the ride changes for each adjustment. When you're adjusting settings, make a note of your starting point for each setting so that you can go back to it if you foul up or find that you don't like the changes that you made.