Rockshox Dual Position (solo) Air

jimothy78
jimothy78 Posts: 1,407
edited August 2013 in MTB workshop & tech
Does anyone know how this technology works? I'd assumed that switching to reduced travel would effectively stiffen the spring to allow for the reduction in available travel, but my experience is suggesting otherwise.

I've got a secondhand Revelation RL (2011 I think). Had been riding them on the reduced travel setting (about 120mm exposed stanchion) and found they were using up all their travel really easily, pushing the o-ring to within a couple of mm of the crown. Switched to the full travel option (about 140mm exposed stanchion) and on the same trails they're using the same length of travel (leaving the o-ring about 30mm from the crown).

This seems to me to make the fork much more susceptible to being bottomed out on the reduced travel setting - is this how it should be, or does something seem amiss?

Comments

  • drtobiasfunke
    drtobiasfunke Posts: 95
    The 120mm setting is really only for climbing.
    http://www.sram.com/rockshox/technologi ... sition-air
    Radon team 7.0
  • benpinnick
    benpinnick Posts: 4,148
    The DP are known to suffer travel issues. I believe the problem stems from the air in the positive chamber leaking into the negative (or vice versa). My advice would be to convert them to DP coil, which is way more reliable and a simple enough job.
    A Flock of Birds
    + some other bikes.
  • jimothy78
    jimothy78 Posts: 1,407
    drtobiasfunke wrote:
    The 120mm setting is really only for climbing.
    http://www.sram.com/rockshox/technologi ... sition-air
    Yes, which is why I imagined it should stiffen the spring rate along with reducing the travel. Can anyone confirm this, or am I barking up the wrong tree?
    benpinnick wrote:
    The DP are known to suffer travel issues. I believe the problem stems from the air in the positive chamber leaking into the negative (or vice versa). My advice would be to convert them to DP coil, which is way more reliable and a simple enough job.

    As they're solo air, aren't the positive and negative meant to be at the same pressure?

    I'm in the middle of a service now (new seals, o-rings and lube all around), so maybe that may help if any air was getting into the wrong places. However I must admit the that all the o rings look to be in good nick and there was plenty of grease around the place. no signs of damage to any of the other bits and bobs, either. Very little oil in the spring side lower, though, but not sure that that could have caused the problem?

    Might consider the coil option if I get really stuck, but would like to avoid that if I can.
  • benpinnick
    benpinnick Posts: 4,148
    Yes they are meant to be the same pressure, but if air leaks (one way) then under compression the air will flow from one chamber into the other, then not return that air back again, causing an inbalance, which then causes the issue.
    A Flock of Birds
    + some other bikes.
  • jimothy78
    jimothy78 Posts: 1,407
    benpinnick wrote:
    Yes they are meant to be the same pressure, but if air leaks (one way) then under compression the air will flow from one chamber into the other, then not return that air back again, causing an inbalance, which then causes the issue.

    gotcha ;)
  • drtobiasfunke
    drtobiasfunke Posts: 95
    jimothy78 wrote:
    drtobiasfunke wrote:
    The 120mm setting is really only for climbing.
    http://www.sram.com/rockshox/technologi ... sition-air
    Yes, which is why I imagined it should stiffen the spring rate along with reducing the travel. Can anyone confirm this, or am I barking up the wrong tree?

    No it wont be stiffer. It says as much in the link I posted.
    It changes your fork’s travel up to 30mm without changing its small bump performance
    Radon team 7.0
  • jimothy78
    jimothy78 Posts: 1,407
    So you think it's designed to be just as soft through the whole of the 120mm reduced travel as it is through the first 120mm of the full travel? Seems to leave the fork open to a lot of bottom-out risk if you hit an unexpecting stone, log etc whilst climbing? I had imagined that they stressed "small bump performance" in that sentence because the spring would ramp up more quickly on larger bumps, rather than just use up all the available travel...

    oh well, I suppose I can always use some compression damping in tandem with the reduced travel to help stiffen it up a bit...
  • drtobiasfunke
    drtobiasfunke Posts: 95
    Pretty much, its not adjustable travel in the sense you're thinking it is, the 120mm setting is just their for some ease with the climbs.
    Solo air equalises the pressure you put in between the positive and negative chambers, so I assume when you lock it in to 120mm mode it equalises both chambers back to whatever PSI you put in originally keeping the small bump response you previously had, so you basically have a fork set up with air pressure and correct sag for 150mm, you lock it to 120mm and you still have the pressure and sag for 150mm travel.

    Doesnt the revelation RL have the 3 position lockout on it? so you can have it locked out or set at threshold for climbing? that should stiffen it up.
    Radon team 7.0
  • jimothy78
    jimothy78 Posts: 1,407
    drtobiasfunke wrote:
    Doesnt the revelation RL have the 3 position lockout on it? so you can have it locked out or set at threshold for climbing? that should stiffen it up.

    Not this one - it originally had the standard on/off (or on/a-little-bit-on) remote, and the main reason for stripping it down at the moment is to disengage the return spring on the MotionControl and fit a dial instead of the remote, in the hope that it will give finer control of the damping circuit, as discussed here.
  • jimothy78
    jimothy78 Posts: 1,407
    Ok, new question.

    Lets say (hypothetically speaking) that i wanted to try running the fork in the reduced travel setting all the time - presumably in this situation I'd be better off increasing the air pressure to give 25% of the reduced travel as sag, instead of 25% of the full travel?

    What d'you reckon?
  • mac-cos
    mac-cos Posts: 80
    jimothy78 wrote:
    Ok, new question.

    Lets say (hypothetically speaking) that i wanted to try running the fork in the reduced travel setting all the time - presumably in this situation I'd be better off increasing the air pressure to give 25% of the reduced travel as sag, instead of 25% of the full travel?

    What d'you reckon?
    simple answer would be set to reduced travel and measure the sag same as you would for setting sag in full travel setting. See what pressure is need to get the sag you want and if it doesnt exceed the pressure settings on the fork sag chart (i'd check this in both settings) then it should be ok.
    Norco Aurum 3 viewtopic.php?f=10017&t=12939531

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