# Thread: Seek formula for figuring out front & rear shock pressure for ECDM

1. ## Seek formula for figuring out front & rear shock pressure for ECDM

Relevant specs: ECDM with Marzocchi 55ATA Fork and RP3 shock. I normally ride with my wife, but sometimes want to give some bike buddies a spin; for them, the settings don't have to be perfect.

These are the instructions that Alex wrote me for setting pressure for myself and my wife (our ride weight is about 240 pounds plus clothes and gear):

You’re looking for 20% sag in the suspension. Use a zip tie on the fork stanchion and shock body, not too tight but enough to be snug.
Start with 35 on the fork and 125 in the shock. Both of you get on the bike without bouncing it, then get off gently and see where the zip ties are. Once you change the preload on the front, the rear preload will be affected (and vice-versa).
Once the sag is set, you can fine tune it to your preferences. 20-25% sag is typical, lighter teams tend to prefer less.

I'm looking for a way to calculate the starting psi numbers, and skipping the part dealing with measuring sag.

Thanks!
Mark

2. Originally Posted by moshemark
I'm looking for a way to calculate the starting psi numbers, and skipping the part dealing with measuring sag.
Setting sag isn't any more involved that Alex's instructions, and is pretty crucial to getting the right performance from your suspension. IME there's no way to predict the correct numbers; Alex's suggestions for starting points are as good as any*. We're about another 125 pounds ride-weight and run 45lb in our Marz 66SL and ran 175 when we had the RP3. I'd imagine you could easily change those happy figures depending on the rest of your suspension settings (comp/rebound, oil weight up front, etc.).

*If you didn't want to check sag, you'd just end up setting pressures and taking it for a ride to see how it reacts. Adjust, rinse, repeat. Once you find the happy figures, it should be pretty consistent from there.

3. Mark, the setup of an ECDM for an exact pressure can and will vary from pump to pump, and also team to team.

One other factor is the year of the rear damper and if it has a large air sleeve or small air sleeve. This is assuming it is a modern ECDM frame.

If you want a base point with no measuring, kind of work sag in reverse...start high, say 230 PSI, with a stand for your stoker beside her, adjust the pressure down ward until the damper just moves slightly with the stoker weight.

Be sure to note the pressures at each point as it drops from the pump install depleting the pressure.

When you add in your weight, it should be acceptable. If not add or subtract as needed.

A sag of 20% is not in anyway mandatory, just a baseline setup with a small window of tolerance each side of 20%.

PK

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