• This topic has 23 replies, 15 voices, and was last updated 3 days ago by ogden.
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  • How can a 160mm fork only showing 145mm of stanchion still have 160mm of travel?
  • Premier Icon cheekysprocket
    Subscriber

    I’ve just installed the 2019 Debonair air spring upgrade to my 2018 Lyrik RCs, in order to reduce their 170mm to 160mm for my new Bronson frame. While the 170mm version perhaps sat 5mm into its travel, I’ve noticed the ?upgraded 160mm airshaft now sits about 15mm into its travel at rest before I’ve even sat on it. (Unless I lift the front wheel and pull down on it.) The fork looks pretty much identical now to the Fox 34 140mm on the bike sat next to it. When I emailed the supplier, he explained that it’s a feature of the negative air spring, and what makes the small bump sensitivity of the fork so good. He added that it’s still got 160mm travel. I understand and appreciate that to a point, but am struggling to understand how a fork that at rest has about as much stanchion showing as a 140mm fork of another brand, is still considered suitable from a frame speccing a fork of at least 160mm. And to ride it just feels steep and horrible at the front. And I guess it will do, given that it’s got less travel (that I can see) than the 150mm shock out back.

    I know Rockshox introduced the 2021 air shaft upgrade a few months ago for those who wanted to reduce their fork’s off the top sensitivity, but I’m starting to wonder if it’s because they’ve still not quite got the negative/positive air chamber thing right, but don’t want a raft of warranty claims on their hands.

    Any experiences/thoughts? Am I failing to see the emperor’s new clothes, and is a trip to Specsavers on the cards?

    (Plan B is just to pop the 170mm shaft back in there (the Bronson takes 160-170mm), and just go ride my bike.)

    BearBack
    Member

    Perhaps on rebound it extends fully, momentarily, ready for the next hit?

    alan1977
    Member

    maybe it doesnt sit in its sag so readily?
    i often wondered if you just ran a longer travel fork, at lower pressure, with more tokens, if you’d end up in the same place as a lower travel fork..

    trumpton
    Member

    Does not sound right to me.just run it at 170mm or your screw up the geometry.

    Premier Icon joebristol
    Subscriber

    I’d empty all the air out and then refill it bit by bit and cycling the fork between each increase. Debonair will sit down furthe in the travel but not that much in my experience. It may not have fully equalised the positive and negative springs. Maybe pump to 40 psi then take the pump off and bounce the fork up and down a few times as deep into the travel as you can – then up another 20 psi then do the same again. Then pump up to your desired pressure and then see where they sit.

    The 2021 debonair spring changes where the piston sits in relation to the notches on the inside of the stanchion to avoid this very issue – it equalises the positive and negative better so makes the fork ride higher in its travel. You can retrofit some of the new bits onto your 2019 airshaft for about £25 I believe.

    Premier Icon Jordan
    Subscriber

    Doesn’t sound right at all to me. Is it the correct part? When you say you can lift it up and pull the wheel down to get the full stanchion showing, does the wheel then spring back up when you let go of it while still off the ground? If so it sounds like there is too much pressure in the negative side somehow.

    Edit: if you have been lowering the pressure in the main chamber you still need to cycle the fork to equalise the neg and pos side. This could cause it.

    stevextc
    Member

    Grease blocking the pos to neg valve?
    Airshaft not fully extended when you put it in?

    Disagree with comments above. Sounds spot on for RS debonair. I have a 150 pike which sits at 10% sag plus under weight of bike. I think the footnut is longer on the new airshaft and -ve volume less. Annoying isn’t it and some suspect the new airshaft is just masking this feature, as opposed to an ‘upgrade’.

    Premier Icon ta11pau1
    Subscriber

    If both forks are set to the correct amount of sag, it won’t matter.

    Why does it matter how it sits when you’re not riding? It’s likely to go past the unweighted sag point when tracking into a hole or under rebound anyway.

    bear-uk
    Member

    The latest debonair kit will make it sit at topout but will make the top harsh and the middle softer according to the reviews. Strangely my 2019 shaft only sags about 3mm and that’s on an ebike.

    poah
    Member

    often wondered if you just ran a longer travel fork, at lower pressure, with more tokens, if you’d end up in the same place as a lower travel fork

    you’d end up with crap handling fork.

    My Yari sit 10mm into it’s travel after having a luftkappe fitted. Explained to me it’s the fork sitting under its own weight. Once you go over a bump or get a bit of air the fork extends back to its full travel on rebound so the loss of travel doesn’t really matter in practice. Pumping the fork with only a small amount of air, pulling up on the fork brace to fully extend the fork and letting go should exaggerate and illustrate the fork settling under its own weight.

    Premier Icon Jordan
    Subscriber

    I knew I had seen something about this. Have a look here Link

    Premier Icon cheekysprocket
    Subscriber

    Cheers for the input guys. Some interesting comments. I’ve had the fork apart and made sure I eyeballed the tube for any scratches that may be causing air leakage. I’ve only greased the pistons as much as recommended, to avoid gamming up the transfer port. I’ve also set it up meticulously as per the Sram video, to ensure the negative air pressure is properly set. Then, once the fork was assembled and sat too low, I’ve done the compressing and suddenly pulling up trick to clear any blockage from the transfer port, all to no avail.

    All in all, I’m not convinced Sram have got this issue nailed, and I’m sorry now to be sitting with a £42 airshaft ‘upgrade’ that makes my bike ride like a dog. The retailer I bought it from has told me it’s a feature not a fault, and so I guess I’ll just sling it on eBay, and go back to the old 170mm air shaft and have done with it. Hey ho.

    Premier Icon fathomer
    Subscriber

    Like ta11pau1 says, if you set the sag at say 25%, surely it makes no difference where it suits when you’re not on the bike?

    Premier Icon cheekysprocket
    Subscriber

    Cheers Jordan. I’d seen that too, when the upgrades came out a few months ago. I still can’t help but read it as ‘here’s a shiny new product for you to buy to make your already expensive fork work properly’.

    I’ve always had Fox forks up until this point, and never had an issue with them sitting into their travel under their own weight. Which is why it’s galling being told that a 160mm Rockshox fork showing the same exposed stanchion length as the 140mm Fox 34 alongside it, still has 160mm of travel. A fork that sags almost 20% under its own weight is hardly going to regain that travel under rebound with me sat on top of it riding along. And then there’s the steepened head angle before you’ve even climbed on and weighted the whole lot even further.

    This argument just doesn’t make sense to me.

    I’d guess the begative chamber isn’t equalised right and forks are sucking down, port might be blocked

    Premier Icon Jordan
    Subscriber

    Still sounds like something wrong to me if you have to pull the wheel down when it’s off the ground. I assume you mean lifting it off the ground by the bars and pulling the wheel down with another hand? The weight of the bike is not affecting it at all in that scenario.

    Premier Icon ta11pau1
    Subscriber

    If it’s really bothering you, then:

    I’d guess the begative chamber isn’t equalised right and forks are sucking down, port might be blocked

    Probably some grease in the port when the old air shaft was removed/new one was put in.

    Premier Icon cheekysprocket
    Subscriber

    ta11pau1, yup, already made sure that isn’t the issue, as per my posts above.

    I’m fast drawing the conclusion there’s a good reason Sram released the 2021 air spring upgrade to much fanfare earlier this year.

    Premier Icon Jordan
    Subscriber

    I’m pretty sure I read another article on STW that said the 2021 upgrade was in response to users complaining about the sag under bike weight issue.

    homatron
    Member

    Have you tried burping the lowers with the old cable-tie down the stanchion trick? Solved a similar issue on my pikes and takes 30 seconds to try it.

    poah
    Member

    when you refitted the lowers did you screw them on with the legs extended or compressed?

    ogden
    Member

    It’s an issue with the 2020 debonair spring, there’s a whole thread on here about it! That’s the whole reason they brought out a 2021 updated version.

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