Viewing 7 posts - 1 through 7 (of 7 total)
  • Setting Up Forks
  • ourkidsam
    Free Member

    I have what I think are dual air Pikes (+ve and -ve air chambers, rebound adjust, compression adjust and the little blow off adjuster)

    I've only ever had a set of mx comps before where I could change how much air was in them.

    First of all, these are pre-owned forks so will have been set up by the previous owner. They feel fine. Should I start messing about with them given that I don't really know what feel I'm expecting to achieve? Or will I find what feels good if I do start playing with them? And if the latter, where do I find the details of what to do and how to do it?

    goldenwonder
    Free Member

    Get on to Sram's website & download a user manual from there.
    Should be a table of air pressures though on the back of l/h fork lower giving details of rider weight & pressures. If you do that, check the pressure as it is now, then dump all air out of both chambers, start from scratch & inflate +'ve before -'ve

    LoCo
    Free Member

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    PeterPoddy
    Free Member

    From one of my RS guides –>

    Correct Setting of Rock Shox Air Pressures

    There seems to be some confusion regarding how to set up Air Sprung Rock Shox forks. This guide refers to any of the Dual Air or Air U-Turn forks. Solo air ones are immune to most of these issues as the negative spring sets itself. However, the section regarding sag and basic pressure still applies

    Sag and Air Pressure

    I find RS recommended pressures are generally on the high side. A good starting point is to set them at the lowest pressure given for your weight range and go from there. This could easily be still too high.

    If it’s a new fork, give it a couple of rides to bed in a little and then do the following –

    Set the sag

    This is possible to do on your own, but easier with a helper. It’s also a lot easier on U-turn forks because they have makings on the side and you don’t need a cable tie. Remove the cable tie when you are done as on a REALLY big hit the seal will (Believe me – It will!) go all the way up to the crown and the tie could damage it.

    • Put a cable tie round one of the fork stanchions.

    • Sit on the bike, in your riding position.

    • Push the cable tie down to the dust seal.

    • Carefully get off.

    • Measure the distance between the seal and the cable tie.

    Realistically you need between 20-30% of the fork travel as sag, depending on the type of riding you do and the travel of the fork. 80-100mm race forks aim for 20%, maybe even a touch less. For 140mm + forks, go for 25-30%. You get the picture.

    OK, so now you’ve set the sag remember the pressure you’ve used OK?

    Setting Positive and Negative Pressures Correctly

    • Use this section in conjunction with setting the sag as above

    This is where it all goes a bit Pete Tong. “I’m loosing travel” is the most common complaint. This is generally not a problem with the fork, but because you’ve set the pressures incorrectly or in the wrong order. Yup, seriously.

    First off, don’t set more negative air pressure than positive. Or if you do, expect to loose a few mm of travel and don’t complain about it, OK!

    The reason for this is simple – Imagine a chamber with a floating piston near the bottom. Your positive air is in the top, above the piston, and when you pump air in it extends the fork to it’s maximum travel and it stops there, no matter how much pressure you put in.

    The function of the air below the piston is primarily to overcome the resistance in the seals. If you put more air pressure in the lower half, you have an imbalance and the pressures will try to equalize, and they can only do this by moving that piston! This will pull the fork down a bit: Not very much as the negative chamber is comparatively small, so a small movement will equalize the pressures. But they will try to equalise. In a way it’s a waste of time to add more air in the negative chamber to “make the fork plusher” as all that happens is you end up with less travel and 2 equal pressures anyway!

    So, how to get the balance right and NOT loose any travel?

    When setting sag as above and making changes to the pressures, do it all in this order –

    1. Let out some of the air from the negative chamber. (The fork may well extend visibly as you do this – “Ay-up, there’s my lost travel!”)

    2. Make your adjustment to the positive pressure.

    3. Pump up the negative chamber again, to the same pressure as you just put in the positive chamber. (If you really want to see what happens, put a lot higher pressure in than you did in the positive chamber and watch the fork drag down as you do, keeping the pressures equal!)

    4. Ride round a bit to settle the fork, and then recheck the sag.

    5. If incorrect return to Step 1.

    6. When checking pressures always do it like this and you’ll have no problems.

    Variation

    Try setting 5, 10, 15…… psi LESS negative than positive air pressure. It will make the fork feel different and you may like it. I do this on my Pikes and they seem to stay just as supple, but dive less readily which I like.

    joolsburger
    Free Member

    I always set my sag standing on the pedals otherwise the forks are too soft I find..

    glenp
    Free Member

    Agree with that – set the suspension up for the way you will be riding – ie on the pedals.

    ourkidsam
    Free Member

    Cheers guys – specially Peter, that looks like it's come from experience!

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