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Fox float air spring spacers

ThePriory1978ThePriory1978 Posts: 563
edited June 2012 in MTB workshop & tech
Hi, I am after advice on Fox float air spring spacers.
http://www.mojo.co.uk/airspacers.html

I have a fox float RP2 on my 140mm travel trail bike (horst link) which I run at 200psi for my riding weight (12 stone) which gets me about 20mm sag.

Problem is I’m blowing through my travel far too easily, almost everytime I hit or drop something any bigger than 2-3 foot I’m bottoming it out. No clunk or anything, it feels bottomless I guess because of the boost valve but i surely shouldn’t be blowing through travel quite this easily?

The bike rides great through small/medium bumps but bigger jumps and drops are a problem.
I have tried up-ing the pressure to 250psi and all tho this improves matters (but dosent solve it) I destroy my ride quality as I basically get no sag at this pressure.
Pro-pedal on or off it makes little difference when hitting the bigger stuff.

Anyway my question Is would Fox float air spring spacers improve matters???

What I am after is probably the impossible. Nice small bump compliance at the top, without being supported in the middle of the travel all the time, but still with mass’s of ramp up pressure in reserve for when I hit big stuff.

Please can somebody explain what Fox float air spring spacers actually do?
And which of the three sizes I would require?
And will Fox float air spring spacers even help or do I need a PUSH tune or something else?

http://service.foxracingshox.com/consum ... e%7CVOLUME

Many thanks in advance
Mark.

Snot green Canyon Nerve AM 8.0x

Posts

  • Dirtydog11Dirtydog11 Posts: 1,621
    edited June 2012
    They may help.

    They reduce the internal air volume which in turn causes the spring to ramp up (get stiffer)sooner in the stroke. I fitted some to my 5 to provide some mid stroke support but found they reduced overall travel.

    If your bottoming out your shock then they may be worth a go, I wasn't.

    I suspect my issue is damping related.
  • nicklousenicklouse Posts: 50,675 Lives Here
    they reduce the size of the air chamber making the spring ramp up faster that it does now. but you will lose some small bump compliance as the air chamber is smaller you will need a higher pressure to start with.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • 386ka386ka Posts: 479
    I think that they are just what you need. Alternatively, you can pour more float fluid in the air can, to reduce the size of the air chamber, effectively the same as air spring spacers.
    But are there any side effects of more float fluid, IDK.
    A much loved, Giant Trance X3 2010
  • So with this
    Dirtydog11 wrote:
    I fitted some to my 5 to provide some mid stroke support but found they reduced overall travel.

    And this
    nicklouse wrote:
    they reduce the size of the air chamber making the spring ramp up faster that it does now. but you will lose some small bump compliance as the air chamber is smaller you will need a higher pressure to start with.

    The spacers will in effect do nothing differently to adding another 10-15psi to my regular 200psi set-up but I get the added ‘bonus’ of a bit less travel.

    Doesn't sound like they are gunna add any benefit...

    But then
    386ka wrote:
    I think that they are just what you need.

    Confused

    Snot green Canyon Nerve AM 8.0x
  • 386ka386ka Posts: 479
    Nope, I think you won't need higher pressure to start with. The pressures will remain the same, but the air can volume will be smaller, so the spring curve will ramp up more towards the end.
    PS, what Air can is on it ATM? Normal volume or XVV?

    And, as I am informed, you will be able to install/uninstall the spacer just by unscrewing the air can. So no need of Mojo or Push.
    A much loved, Giant Trance X3 2010
  • nicklousenicklouse Posts: 50,675 Lives Here
    So with this
    Dirtydog11 wrote:
    I fitted some to my 5 to provide some mid stroke support but found they reduced overall travel.

    And this
    nicklouse wrote:
    they reduce the size of the air chamber making the spring ramp up faster that it does now. but you will lose some small bump compliance as the air chamber is smaller you will need a higher pressure to start with.

    The spacers will in effect do nothing differently to adding another 10-15psi to my regular 200psi set-up but I get the added ‘bonus’ of a bit less travel.

    Doesn't sound like they are gunna add any benefit...

    But then
    386ka wrote:
    I think that they are just what you need.

    Confused
    nope they will work differently as the air volume is smaller it will ramp up faster. not the same as adding air.

    they should not reduce travel unless you are too light.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • 386ka386ka Posts: 479
    IMHO it can even improve small bump sensitivity, as it allows for a lower air pressure to start with, without bottoming out..? Or is my logic on vacation? :D
    A much loved, Giant Trance X3 2010
  • YeehaaMcgeeYeehaaMcgee Posts: 5,740
    386ka wrote:
    IMHO it can even improve small bump sensitivity, as it allows for a lower air pressure to start with, without bottoming out..? Or is my logic on vacation? :D
    Definitely your logic on vacation.
    Think of a tiny, skinny road bike tyre at 15PSI - it will look like an used condoom when you sit on the bike.
    Now take a big manly MTB tyre, and inflate to 15PSI. Although it'll be soft, it will actually hold your weight up.

    By reducing the air chamber size, you're reducing the area. Area is measured in square inch.
    Pressure is pounds (of force) per square inch - PSI. Reducing the area neccesitates an increase in pressure.
  • YeehaaMcgeeYeehaaMcgee Posts: 5,740
    almost everytime I hit or drop something any bigger than 2-3 foot I’m bottoming it out.
    Sounds perfectly normal. This can happen even with long travel DH bikes. Your impact with a 3 foot drop is significantly larger than a 6 inch drop.
    Suspension doesn't mean you don't have to have a little finesse when landing drops.
  • 386ka386ka Posts: 479
    Lol, no. Think of it this way. When you are going to a smaller air chamber, you need lesser quantity of air to get to the right pressure, as with a bigger air can.

    The reducing of the area does not require a higher pressure! How would you say that, when the pressure is relative to the force distributed on a square inch?
    It's like saying that at a constant pressure, there is more force per square inch in a bigger air can, than in a smaller one?!
    That said; there are instances when an air spring cannot be satisfactorily tuned because a rider is too heavy for a particular suspension design, would like to use less air pressure without bottoming the suspension, or may want the shock to perform outside of the limitations imposed by the volume of its stock air canister.

    http://www.pinkbike.com/news/tech-tuesd ... -2011.html

    EDIT: Read lower in the the text too, and you will be proven that my logic is not on vacation (yet). :D
    A much loved, Giant Trance X3 2010
  • YeehaaMcgeeYeehaaMcgee Posts: 5,740
    Eh, Less quantity of air in a small can is a given, yes. Because it's smaller.
    But a smaller container needs more pressure to hold the same weight.

    Back to the tyre analogy. On a small road bike tyre your weight may be supported by, say 0.25 square inches.
    On a mountain bike you're supported by a full square inch (figures are plucked from the air, but will suffice for comparrison).
    The road tyre will require 4x the pressure to support an equal load.

    It's the reason someone wearing stilletos will sink into a field, but will be fine barefoot. And it's how snow-shoes (and skis and snowboards) work.
  • FBM.BMXFBM.BMX Posts: 148
    edited June 2012
    The tyre analogy is incorrect. You are not changing the CSA of the surfaces of which the air is applying pressure to in reaction to compression, hence force. The only change by adding a spacer is volume.

    Since -

    Pressure = force / CSA

    Force = Pressure X CSA

    CSA is not changing.

    In the simplest sense, assuming no heat effects, the spring characteristics behave in the manner -

    P1V1 = P2V2

    Or rearrange this -

    (P1V1)/V2=P2

    This shows the smaller V2 is, the bigger P2 is. The bigger P2 is, the larger the force required to compress the air volume.

    It is also right to assume you can run a softer beginning stroke and attain greater bottom out resistance with a smaller air can volume. It can be simply demonstrated by looking at the equation immediately above.

    OP - What frame is it? What is the current air can, HV or standard?

    It does indeed sound like an air volume spacer will help you out.
  • As good as it is to illustrate the point.
    I. hate. maths. Just saying.

    I have a Fox Float performance RP2 Boost Valve XXV High volume run at 200psi on a horst link 140mm travel bike.

    Snot green Canyon Nerve AM 8.0x
  • FBM.BMXFBM.BMX Posts: 148
    As good as it is to illustrate the point.
    I. hate. maths. Just saying.

    I have a Fox Float performance RP2 Boost Valve XXV High volume run at 200psi on a horst link 140mm travel bike.

    I would say the high volume shock maybe the cause of your troubles. Specifically what is your frame? Horst link doesn't really help things out, they can be designed to operate in an infinite number of ways.

    With you HV air can, you can remove the exterior can and pack it out to reduce the volume to see what it will be like. i've done this before as have many friends i have recommended it to with good results. I used thin plastic sheet as packing material, you use grease too, well anything incompressible.
  • It is a Canyon Nerve AM frame.

    Snot green Canyon Nerve AM 8.0x
  • chez_m356chez_m356 Posts: 1,893
    so what have you done to the shock to go from this
    The rear shock dosent seem to use all its travel so its essentially a 150mm fork 130mm shock bike. Got to figure if this is a frame design flaw or a shock problem to get the 140mm it should have.
    to this
    Problem is I’m blowing through my travel far too easily, almost everytime I hit or drop something any bigger than 2-3 foot I’m bottoming it out. No clunk or anything, it feels bottomless I guess because of the boost valve but i surely shouldn’t be blowing through travel quite this easily?
    ?
    Specialized Hardrock Sport Disc 10- CANYON Nerve AM 6 2011
  • YeehaaMcgeeYeehaaMcgee Posts: 5,740
    FBM.BMX wrote:
    The only change by adding a spacer is
    Are the spacers a kind of foam then? I was gussing that they reduced the internal size of the air chamber - which would definitely redue the surface area.
  • chez_m356 wrote:
    so what have you done to the shock to go from this
    The rear shock dosent seem to use all its travel so its essentially a 150mm fork 130mm shock bike. Got to figure if this is a frame design flaw or a shock problem to get the 140mm it should have.
    to this
    Problem is I’m blowing through my travel far too easily, almost everytime I hit or drop something any bigger than 2-3 foot I’m bottoming it out. No clunk or anything, it feels bottomless I guess because of the boost valve but i surely shouldn’t be blowing through travel quite this easily?
    ?

    First subject was me being a doofus.

    Second subject was after me being educated so i'm talking truth not bobbins.

    Snot green Canyon Nerve AM 8.0x
  • FBM.BMXFBM.BMX Posts: 148
    FBM.BMX wrote:
    The only change by adding a spacer is
    Are the spacers a kind of foam then? I was gussing that they reduced the internal size of the air chamber - which would definitely redue the surface area.

    It's not the pressure in all directions that produces the spring force, it's only the pressure acting on the ends that that count. It's these end surfaces that are not changing in surface area.

    http://linkagedesign.blogspot.co.uk/2011/10/canyon-nerve-am-2012.html

    OP- Your leverage rate is only slightly progressive, good for coil, good for mid volumes air shocks in a general riding application (this is my opinion). Not good for small volume air cans unless you freeride and need bottom out resistance, not good for HV air cans unless you're very light or ride canal paths and are after a "plush" ride and want to use all the travel easily.

    I'd just rmove the exterior air can, pack it and i reckon it'll be just what you're after.
  • FBM.BMX wrote:
    OP- Your leverage rate is only slightly progressive, good for coil, good for mid volumes air shocks in a general riding application (this is my opinion). Not good for small volume air cans unless you freeride and need bottom out resistance, not good for HV air cans unless you're very light or ride canal paths and are after a "plush" ride and want to use all the travel easily.

    I'd just rmove the exterior air can, pack it and i reckon it'll be just what you're after.

    Thanks for the advice. Very much appreciated.

    But how do i 'pack it' and what with? I'm a little dubious about filling my shock with plastic bags when its such a technical and expensive bit of kit.

    I've seen this vid from pinkbike http://www.pinkbike.com/news/technical- ... -2010.html so i can follow that to dissamntle the high volume shock and I understand how to fit spacers.
    So would you recommend i try the smallest of spacers or can you give me 'packing instructions'?
    Thanks

    Snot green Canyon Nerve AM 8.0x
  • Does look simple as. Cheap and effective :-) Will certainly have a proper read of that article and give it a go. Thanks.
    Unfortunately i dont have access to ski base repair material so will have to have a think about an alternate suitable un-compressible material.

    Snot green Canyon Nerve AM 8.0x
  • YeehaaMcgeeYeehaaMcgee Posts: 5,740
    FBM.BMX wrote:
    Ah, I see. It's much simpler than I'd thought, and yeah, that does make sense now I see what you mean. :oops: :D
  • chez_m356chez_m356 Posts: 1,893
    FBM.BMX wrote:
    Ah, I see. It's much simpler than I'd thought, and yeah, that does make sense now I see what you mean. :oops: :D
    this is not intended as a snidey comment, but that link is almost 6 years old, has the technology not advanced since then?
    Specialized Hardrock Sport Disc 10- CANYON Nerve AM 6 2011
  • cooldadcooldad Posts: 32,599
    Haven't looked at the link, but if it's what I think, an aircan is an aircan is an aircan.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • cooldadcooldad Posts: 32,599
    Does look simple as. Cheap and effective :-) Will certainly have a proper read of that article and give it a go. Thanks.
    Unfortunately i dont have access to ski base repair material so will have to have a think about an alternate suitable un-compressible material.
    Mr P, anything really will do. Last time we fiddled with thel33ter's, we used a bit of plastic stiffener packaging stuff from the collar of a new shirt.
    It just has to take up space, but a flexible bit of plastic doesn't bounce around, so better than marbles.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • FBM.BMXFBM.BMX Posts: 148
    Yep an air can is an air is an air can.

    As for suspension tech in general, nothing is complicated or magic. Everything is old, basic, age tested designs borrow from automotive or motorcycles, re-jigged for cycling application and re-marketed.
  • 386ka386ka Posts: 479
    Also, consider the idea of putting more float fluid. Cheap and the fluid is incompressible.

    @Yehaa, see? :D If you were to use smaller pistons, then yes, you would need bigger pressure to suspend the same weight.
    But when you are changing the chamber volume, you don't need to. :)
    A much loved, Giant Trance X3 2010
  • georgeslogeorgeslo Posts: 15
    Hi, I see you're riding a nerve AM......the same as me.....I am a heavy rider and ride a talas 36 up front

    The XXV air can on these bikes do tend to cause a "flexy" feeling of the rear, i was quite surprised as the linkage suspension ratio on this bike is approx 2.75. I was almost always riding with the propedal "on".

    I had the same issue as you. Before, I didn't bottom out too frequently, once or twice on every other ride, but the mid stroke feeling was a disaster.

    I installed a medium fox spacer and with the same air pressure , my sag went from 20% to approx. 25%. but the mid stroke feeling improved ALOT....it ramps up faster and feels much stiffer....however I still use all of the travel.

    In my experience best spent 30 euros :D
  • Thanks for the opinion.

    I have the spacer kit on order from Fox, currently everywhere is sold out so i've gone direct but am still expecting a month before delivery.

    Cant wait to fit and forget.

    Snot green Canyon Nerve AM 8.0x
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