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  1. #1
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    What's the extra sleeve round the aircan of my new shock?

    I've just been given a new shock under warranty. The old one was a Fox Float R but the new one is an RP23 Boost valve Adaptive logic.

    One thing is puzzling me though - there seems to be an extra sleeve around the air can on the new shock that wasn't there on the old one, and I don't know what it does!

    Here's a pic of a similar one with an arrow pointing to the extra sleeve...

    What's the extra sleeve round the aircan of my new shock?-rp23-2.jpg

    Now here's a pic I found showing two RP23s, the one on the left with the extra sleeve, and the one on the right without, so its an option...

    Name:  RP23 (260x260).jpg
Views: 407
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    And here's a cutaway I found showing the sleeve (arrows), and it seems to enclose a separate air space, but not obviously connected to anything else...

    What's the extra sleeve round the aircan of my new shock?-rp23-1-402x600-.jpg

    So, can anyone tell me what it is and what it does

    Thanks.
    Last edited by PerthMTB; 05-06-2013 at 12:11 AM.

  2. #2
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    It is an XV (extra volume) air can. It lets the shock operate in a more linear fashion, due to there being more air in it. Some bike designs work better with a shock that operates in a more linear fashion, and some work better with a standard volume (i.e. more progressive) air can.
    I don't crash, I just have slightly uncontrolled dismounts!

  3. #3
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    Ok, cool. So whether its a good thing to have or not depends on the design of the bike suspension, right? So, any idea if a Giant Trance (26") with their Maestro suspension system is one of those designs that benefits from an XV?

    And, if all it does is increase the air can volume (I'm assuming there's a hole or something between it and the main air can), why the separate sleeve on the outside - surely they could just put a larger 'original' can on much more easily and avoid the complications of two concentric cans with all the extra seals that involves?

  4. #4
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    I know that some designs that are optimised for a standard air volume can too easily blow through available travel with an XV can, and some designed with XV cans will ramp up horribly with a standard can on them, but I'm not sure how the Maestro system would work with/without it, maybe someone in the Giant sub-forum could answer that for you.
    I don't crash, I just have slightly uncontrolled dismounts!

  5. #5
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    OK, I guess as that's the one Giant supplied with the frame (the frame was a warranty replacement and came with a new shock) then they know that an XV can is good for Maestro...

    By the way, just been doing some Googling and can answer the second question myself about why the separate sleeve rather than just a bigger main can. Seems the hole from the sleeve to the main can is only exposed for the first part of the stroke, then the piston covers it for the rest. So, it acts like a larger volume can for the beginning of the stroke, but a smaller volume one for the end. Smart!

    But have also come across some views that whether to go for XV can or not also depends on rider weight. Interestingly though, there didn't seem to be agreement whether XV was better or worse for a heavy rider. I'm 200lbs by the way.

  6. #6
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    What's the extra sleeve round the aircan of my new shock?

    I'm 80kg, have a 26" Trance X, and have a XV can on an RP23.

    I have added air volume spacers to make the shock more progressive. So for my weight I would recommend the normal air can.

  7. #7
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    So am I reading this right - XV can is better for smaller/lighter riders, and anyone about my weight (200lbs/90kg) is better off with normal can? Must admit I've noticed that with the same pressure (180psi) I used to have in my old FloartR, the new one has way more sag, so I've already upped the pressure to 210psi. Is this a sign that I'm too heavy for the XV can and need to add spacers?

  8. #8
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    NO, it's a sign that it's an XV shock, which requires more air volume to work the same You did all that reading and didn't come across this?
    Quote Originally Posted by PerthMTB View Post
    So am I reading this right - XV can is better for smaller/lighter riders, and anyone about my weight (200lbs/90kg) is better off with normal can? Must admit I've noticed that with the same pressure (180psi) I used to have in my old FloartR, the new one has way more sag, so I've already upped the pressure to 210psi. Is this a sign that I'm too heavy for the XV can and need to add spacers?
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  9. #9
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    NO, it's a sign that it's an XV shock, which requires more air volume to work the same You did all that reading and didn't come across this?
    Well excuuuuse me! I'm sure you know all about this stuff, but I'm still learning, that's why I come on a forum and ask stoopid questions - so I can learn. Don't know how you got all those rep points with that kinda attitude.

    So, if you'd like to contribute something useful to this thread instead of just sarcasm, how about explaining what you mean by "an XV shock needs more volume to work the same", and how that relates to needing higher pressure in it?
    Last edited by PerthMTB; 05-06-2013 at 04:28 AM.

  10. #10
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    This is the volume spacer kit that was mentioned above - Changing FLOAT Air Spring Compression

    Also found this little explanation on another site which sort of explains the use of the spacers -

    Why Change the Shock’s Compression Ratio?

    Before we get started, a brush-up on air springs and spring rates may be helpful. Unlike a coil spring, which retains zero energy while uncompressed, an air spring begins at a high, pre-set static pressure. Preload adjustments to change suspension sag do not affect a coil spring’s overall rate, but any changes in air pressure will alter an air shock’s suspension-sag measurement and its overall spring rate at full compression. Because sag and spring rate are bound together, a rider who pumps an extra 50 psi into the air can in order to prevent harsh bottoming must also suffer a harsh ride in the initial suspension travel and a taller ride height due to reduced shock sag.

    Suspension tuners separate the sag and spring-rate functions of an air shock by changing the volume of its air can. Reducing the volume of the air chamber causes the air pressure to ramp up quickly, so the spring pressure can be set low, allowing more suspension sag without risking harsh bottoming. A larger-volume air can ramps up less at full compression, but the shock will sag less because more volume requires significantly higher starting pressures to prevent bottoming at full compression. Fox’s internal spacers allow riders to change the volume of the air spring and fine-tune the spring rate of the shock without replacing the expensive air can, or even removing the shock from the bike.
    Hope that helps a bit more than the "advice" given above
    I don't crash, I just have slightly uncontrolled dismounts!

  11. #11
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    Yes, thanks, very helpful! It's starting to make sense now...

  12. #12
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    What's the extra sleeve round the aircan of my new shock?

    Quote Originally Posted by PerthMTB View Post
    Yes, thanks, very helpful! It's starting to make sense now...
    PerthMTB,

    The standard volume can will be more progressive than the XV can. The beauty of the XV can, is that you can use the relatively cheap air volume spacers to reduce the air volume, until you find the level of progressiveness that suits your frame and riding style.

    At 25% sag, I found the XV can to be fine for general trail riding, but as soon as drops and jumps were hit at speed I was bottoming the suspension too easily. So I added the spacers to make the spring rate more progressive.

    I am now very happy with the performance of the suspension.

  13. #13
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    The standard volume can will be more progressive than the XV can. The beauty of the XV can, is that you can use the relatively cheap air volume spacers to reduce the air volume, until you find the level of progressiveness that suits your frame and riding style.
    Ok, I'm probably gonna show my ignorance again here, but when has that ever stopped me

    So greater volume = less progressive = great small bump compliance, but slower ramp-up.

    With a heavier rider this could result in bottoming out. So, you up the pressure to compensate, which results in loss of small bump compliance at the top end.

    So, an alternative is to reduce the volume by adding the volume reducers. So you still get small bump comppliance, but it ramps up quicker to prevent bottoming out.

    Have I got it right so far?

    But, still one thing I don't quite get then. Van Cuz, you started with an XV can and added volume reducers. Why not just revert to a normal can - wouldn't this have the same effect of just reducing volume?

    Thanks for you your patience in explaining it to me...

  14. #14
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    The big difference with the volume spacers is that you have 3 ways of adjusting the progressiveness of the shock, whereas if you just default to the standard air can, you have only one option with no real way of tuning the air volume (although you probably could use the spacers, but the shock would be so progressive it would to all intents and purposes be un-usable to most riders).
    I don't crash, I just have slightly uncontrolled dismounts!

  15. #15
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    As Kiwiplague has mentioned, the spacer kit gives you options, and is pretty cheap. Also, my bike came stock with a XV can, so using spacers was going to be cheaper than switching cans.

    Small bump compliance is a complex combination of suspension design, spring rate and shock damping. I would do a terrible job of trying to explain it to you.

    Here is a couple of links that may improve your understanding.

    Tech Tuesday - What a Negative Spring is and Why it Makes the Coil-Spring Nearly Obsolete - Pinkbike
    http://www.santacruzbicycles.com/company/joe1207.php
    Linkage Design: Giant Trance 2011

  16. #16
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    Quote Originally Posted by PerthMTB View Post
    OK, I guess as that's the one Giant supplied with the frame (the frame was a warranty replacement and came with a new shock) then they know that an XV can is good for Maestro...

    By the way, just been doing some Googling and can answer the second question myself about why the separate sleeve rather than just a bigger main can. Seems the hole from the sleeve to the main can is only exposed for the first part of the stroke, then the piston covers it for the rest. So, it acts like a larger volume can for the beginning of the stroke, but a smaller volume one for the end. Smart!

    But have also come across some views that whether to go for XV can or not also depends on rider weight. Interestingly though, there didn't seem to be agreement whether XV was better or worse for a heavy rider. I'm 200lbs by the way.
    The reason you don't just make the main air can bigger is that it would also mean using a bigger piston, which would defeat the purpose of increasing the volume. It is not simply the increase in volume that makes the spring less progressive (more linear), rather it is the increase in total volume relative to the air displaced by the piston when the shock compresses. If you just increase the diameter of the air can (piston and all), then you would also be increasing the volume of air displaced when you compress the shock. In other words, the spring curve will not look much different in shape, it would just run at a lower pressure.

    Also, that hole you refer to is (in the shocks I have looked at) not blocked in the early part of the stroke. If it is blocked at all, it would be at the end of the stroke. The increased volume makes more difference the further into the stroke you go, so it would defeat the purpose of having the extra volume it if you block it off too soon.
    15mm is a second-best solution to a problem that was already solved.

  17. #17
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    Quote Originally Posted by PerthMTB View Post
    Ok, I'm probably gonna show my ignorance again here, but when has that ever stopped me

    So greater volume = less progressive = great small bump compliance, but slower ramp-up.

    With a heavier rider this could result in bottoming out. So, you up the pressure to compensate, which results in loss of small bump compliance at the top end.
    To some extent this can be true. Keep in mind, though, that a lighter rider needs lower pressure than a heavier rider to get good bump compliance.

    I theory, as you increase pressure, you increase bottoming resistance, and decrease sag and small bump compliance. However, a heavier person, in addition to needing more bottoming resistance, also can run a higher pressure and still get good bump compliance. Ever ride on a truck that is sprung super stiff to carry heavy loads? It might be a very harsh ride when empty, but with a load, the ride smooths out.
    15mm is a second-best solution to a problem that was already solved.

  18. #18
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    Great, thanks for all the helpful replies. Looks like I'll get a volume spacer kit and have a play at tuning my new shock...

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