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  1. #1
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    Fox Float R vs RP2 vs RP23 question

    I feel ashamed for asking this, given that I've been riding MTBs since 1990 (Trek Singletrack Antelope) but what is the difference between these rear shocks? All my bikes have come with either RP2 or RP23 and I just thought they were the same except for a lockout feature. Are the internals different from model to model?
    02 Giant NRS
    05 Giant VT
    08 Specialized StumpJumper
    11 Giant Reign (converted to 27.5)
    14 Giant Trance 27.5

  2. #2
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    the R has rebound adj and the RL has lockout and the RP2 has 2 levels of PP and on/off and the RP23 has 3 levels of firm adjust of PP and PP on/off

    RP2

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    Last edited by Zoke2; 08-25-2012 at 04:13 PM.
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  3. #3
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    Complementing Zoke2 post, the R has no lock/ProPedal switch. Only thing adjustable is the rebound.

    The way Zoke2 wrote about the RP2 may induce some in error. The RP2 doesn't have 2 levels of ProPedal. It only has one, usually set at medium level from the factory. What the RP2 allows is to select an open shock position (ProPedal not active) and another with ProPedal active.

    The RP23 behaves the same way but allows the user to select the ProPedal level (from 3 available) on the fly. It isn't locked at a predetermined level from the factory.

  4. #4
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    Good stuff here. The only other thing to know is that any of these shocks may have had AVA: Air Volume Adjustment.

    This is a threaded adjuster for the air sleeve, which adds linear spring rate as the volume decreases. By default the shocks have a progressive spring rate, and decreasing AVA makes it more linear. FWIW I like my Float R AVA with max air volume but I'm still learning and tweaking the setup.

  5. #5
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    Quote Originally Posted by ColinL View Post
    Good stuff here. The only other thing to know is that any of these shocks may have had AVA: Air Volume Adjustment.

    This is a threaded adjuster for the air sleeve, which adds linear spring rate as the volume decreases. By default the shocks have a progressive spring rate, and decreasing AVA makes it more linear. FWIW I like my Float R AVA with max air volume but I'm still learning and tweaking the setup.
    I'm confused by your wording "adds linear spring rate as the volume decreases", but it seems backwards - increasing the AVA volume makes it more linear, reducing the volume makes it more progressive (less linear).

  6. #6
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    No, I stated it correctly, although perhaps not eloquently. Read here: http://www.foxracingshox.com/fox_tec...rShocks_en.pdf
    Turning the AVA ring increases or decreases the volume of the positive air spring chamber allowing the rider to alter the shape of the spring curve. The AVA system creates a shock that, in its smallest setting, is up to 30% more linear spring rate than a standard FLOAT shock. AVA allows as much as 200 lbs of adjustment in spring rate from fully closed to fully open when fully compressed.
    Max air volume = progressive
    Min air volume = linear

    What's happening is that instead of the shock looking looking a curve starting low left and bowing up and right (max AVA), you draw a straight line from low left to top right (min AVA).

    To muddy things further...
    The label on the shock, at least on my ~2005 Float R AVA, shows 'INCREASE' as you are actually decreasing the air sleeve volume. The term increase in that case certainly applies to the linear spring rate.

  7. #7
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    If i recall correctly, since 2007 Float shocks don't have AVA cans available.

    Instead you have to opt for a normal volume or an high volume air can and if you still feel the need acquire an air spring spacer kit to further tune the compression rate.

  8. #8
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    fsrxc is correct, the greater the volume of air, the more linear it is. If the volume is reduced, the pressure curve ramps up much faster when shock compresses (or extends in a pull shock).

    Most the newer fox shocks don't have adjustable volume, instead the volume of the air can is fixed but spacers can be installed to take up extra volume to help with bottom out issues on bigger hits.

  9. #9
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    You guys are mistaken. The reason for the progressive curve by default, which is max air can volume, is so that the shock has good small bump sensitivity. A progressive shock (or strut, on a car) is a really good thing. Linear is not good as it will ride harshly.

    But you were partially right. The reason for AVA is to add additional spring rate in case you want to remove small bump compliance, such as for pedaling efficiency or if you are heavy rider. In these cases, adding linear spring rate, as I've quoted above from the Fox manual, is beneficial.

  10. #10
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    Quote Originally Posted by ColinL View Post
    You guys are mistaken. The reason for the progressive curve by default, which is max air can volume, is so that the shock has good small bump sensitivity. A progressive shock (or strut, on a car) is a really good thing. Linear is not good as it will ride harshly.

    But you were partially right. The reason for AVA is to add additional spring rate in case you want to remove small bump compliance, such as for pedaling efficiency or if you are heavy rider. In these cases, adding linear spring rate, as I've quoted above from the Fox manual, is beneficial.
    Thanx ColinL..now my head hurts..
    lean forward

  11. #11
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    You have to look at it in terms of the ratio of the volume at the top of the stroke to the volume at bottom out. The piston, which is a fixed diameter and stroke length, displaces the same amount regardless of the amount of air in the air can. Also, when you change the volume of the can, it takes away (or adds) the same amount regardless of where the piston is in the travel.

    Scenario 1:

    At Top
    Air volume = 6 in^3
    Piston displacement = 3 in^3

    At Bottom
    Leftover volume = 3 in^3

    This means that 6 in^3 at initial pressure have now been forced into half the space.

    Scenario 2 (smaller volume):

    At Top
    Air volume = 4 in^3
    Piston displacement = 3 in^3 (fixed, same as before)

    At Bottom
    Air volume = 1 in^3

    This now puts all the air at initial pressure into 1/4 as much space.

    The smaller volume air can creates a more progressive air spring curve.

    It is possible that someone is referring to the volume taken up by an adjustment instead of what is left, in which case less volume TAKEN UP would result in more volume LEFT OVER, thus more linear air spring curve.

    Sorry for the long winded explanation, I get a little carried away sometimes.

  12. #12
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    Also, sorry for the thread hijack...we've gotten a little off topic from the op.

  13. #13
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    Quote Originally Posted by mtbsam View Post

    ...The smaller volume air can creates a more progressive air spring curve...
    This is exactly the concept I had to do for the mod to my shock...

    But, what is the purpose of "High Volume" then? My Reign has it. I had to add a shim in order to get a smaller volume, thus giving me a more progressive feel. I only weigh 175lbs. Without the shim, I bottom out the shock on relatively small hits (2 ft drop) and that was with 225+ psi. With the shim I'm running about 185 psi.

    I don't mind going off topic
    02 Giant NRS
    05 Giant VT
    08 Specialized StumpJumper
    11 Giant Reign (converted to 27.5)
    14 Giant Trance 27.5

  14. #14
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    High volume is supposed to flatten the curve of the wheel rate for an overly progressive suspension design. Basically, it's using a shock to compensate for a suspension geometry of the frame that makes using the full travel of the bike difficult. You have to get into the difference between rising rate (progressive) and falling rate (not linear, but opposite of rising). Obviously there is a full spectrum when it comes to that as well.

    This suspension rate is why two people with the same shock and weight rarely run the same pressure unless they are on the same bike also. The leverage ratios and rates through the travel in combination with the behavior of the shock are supposed to be optimized by the manufacturer.

    Your Giant Reign is built with Maestro, a relatively progressive suspension design. Giant probably wanted to flatten out the wheel rate with a larger volume shock and may have overshot the target. They may do that on purpose, however, knowing that a volume spacer can be installed and tuned by the user where as with an air can that is too small, you would have to buy the larger can.

  15. #15
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    Quote Originally Posted by mtbsam View Post
    You have to look at it in terms of the ratio of the volume at the top of the stroke to the volume at bottom out. The piston, which is a fixed diameter and stroke length, displaces the same amount regardless of the amount of air in the air can. Also, when you change the volume of the can, it takes away (or adds) the same amount regardless of where the piston is in the travel.

    Scenario 1:

    At Top
    Air volume = 6 in^3
    Piston displacement = 3 in^3

    At Bottom
    Leftover volume = 3 in^3

    This means that 6 in^3 at initial pressure have now been forced into half the space.

    Scenario 2 (smaller volume):

    At Top
    Air volume = 4 in^3
    Piston displacement = 3 in^3 (fixed, same as before)

    At Bottom
    Air volume = 1 in^3

    This now puts all the air at initial pressure into 1/4 as much space.

    The smaller volume air can creates a more progressive air spring curve.

    It is possible that someone is referring to the volume taken up by an adjustment instead of what is left, in which case less volume TAKEN UP would result in more volume LEFT OVER, thus more linear air spring curve.

    Sorry for the long winded explanation, I get a little carried away sometimes.
    All you've shown is that the lower volume can has more air (spring) pressure. That is a given. What you didn't show is a compelling argument for air spring pressure over the travel range of the piston. Smaller volume is more air pressure for any movement of the shock. It adds a linear spring rate.

  16. #16
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    I have done up a quick excel example of what I'm saying. I used very nice clean numbers to start with (which may or may not be reasonable depending on the situation) but the theory holds true. I can also send the .xls file itself to anyone who wants to play with it and see how the variables change the outcome.

    This shows the 2 air spring curves plotted against the stroke of the piston. The High Volume curve is still a curve, but it is much closer to linear and provides less protection against bottom out.

    www.box.com/s/edf1598b783ddb51ed77

    Sorry, I haven't made enough posts to embed the photo or add a link.
    Last edited by mtbsam; 08-30-2012 at 11:25 PM. Reason: Updated post for working link

  17. #17
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    Air pressure at sag will be the same for either HV or LV . Air pressure at full travel will be higher with less volume. The whole shock curve isn't moved up equally at both ends, like adding a linear spring constant K to the whole curve.
    lean forward

  18. #18
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    ^exactly.

  19. #19
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    Help a fatty

    Quote Originally Posted by ColinL View Post
    You guys are mistaken. The reason for the progressive curve by default, which is max air can volume, is so that the shock has good small bump sensitivity. A progressive shock (or strut, on a car) is a really good thing. Linear is not good as it will ride harshly.

    But you were partially right. The reason for AVA is to add additional spring rate in case you want to remove small bump compliance, such as for pedaling efficiency or if you are heavy rider. In these cases, adding linear spring rate, as I've quoted above from the Fox manual, is beneficial.
    Great info thanks. Just to be clear, are you saying that as a heavy rider (230lbs/105kilo) I'd benefit from reducing the air volume to reduce pedal bob at the slight expense of riding over small stuff?

    I'm currently running my blur lt on max volume which doesn't seem to suffer too much from pedal bob but perhaps that could be thanks to the Santa Cruz VPP technology?

    I'm working on the 230lb by the way so yes I know that would REALLY help eliminate pedal bob

  20. #20
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    I'm not sure what I was smoking last year, but I had it backwards!

    Smaller air volume makes an air spring more progressive. Larger air volume makes an air spring more linear.

    Progressive suspension is still useful for a MTB or any off-road use because it can adapt to a wide range of conditions. If you go linear it's easier to use all the travel but if you get it wrong, you could bottom out hard much more easily than a progressive spring rate.

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