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  1. #1
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    Fox RP23 w/ High Volume not performing, upgrade advice

    I have a 2007 Jamis Dakar XAM frame (varies a lot from 2008+ models) that came with a 2010-ish fox float RP23 with a high volume air can. The issue is that no matter how much I stiffen it up by adding more pressure I continually bottom it out on light terrain. With pro-pedal on or not it just all around sucks, too firm for the small bump compliance, and apparently not firm enough so that it bottoms out all the time. It just blows right through the travel and feels harsh.

    I've read around that the high volume air can generally isn't as good as the regular can, but it depends a lot on rider weight and suspension design. I weigh about 175lbs fully geared up, do you think changing the HV can to a regular one would help?

    Also, the frame should have a 7.875 x 2.25 shock but I am pretty sure the one I have is a 7.875 x 2.0 which only gives me about 120mm of rear travel versus the normal 133mm. I released all the air from the shock and compressed it as far as it would go, refilled it and measured from the dust wiper to where the o-ring went and it was 2.0 in. However, after bottoming out while riding, the o-ring goes all the way to the end of the shaft as if it was 2.25in of stroke. How can I tell what the stoke length is for sure?

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    Just found a really good deal on a X-Fusion O2 RLZ that is the correct size and stoke, any idea how that would compare to the RP23? It has a low-volume air can on it.
    Last edited by Dooms101; 01-29-2013 at 12:31 PM.

  3. #3
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    A low volume air can would be a step in the right direction w/ your current shock. You said the stroke is incorrect and didn't mention if it has the correct damper tune. A new shock would allow for full travel and a smaller air volume , X-fusion's generally have a little firmer compression tune.

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    I really have no idea if it is the correct damper, velocity, and compression tune. I bought the frame used and it was on there, I think the guy before me just threw a random shock on there without checking anything. Would a firmer compression tune provide a firmer pedaling platform? Do all the X-Fusion rear shocks come with the same damper tune? I wouldn't really know what tune to use for my bike anyways.

    When it comes to suspension I really only know how to setup the spring rate via measuring the sag, setting the rebound, and setting the low speed compression.

  5. #5
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    Quote Originally Posted by Dooms101 View Post
    I really have no idea if it is the correct damper, velocity, and compression tune. I bought the frame used and it was on there, I think the guy before me just threw a random shock on there without checking anything. Would a firmer compression tune provide a firmer pedaling platform? Do all the X-Fusion rear shocks come with the same damper tune? I wouldn't really know what tune to use for my bike anyways.

    When it comes to suspension I really only know how to setup the spring rate via measuring the sag, setting the rebound, and setting the low speed compression.
    Best bet would be to call X-fusion as they make aftermarket & oe tuned shocks. Personally I like RP23's as you can further tune the air volume's via spacers and there is always custom tuning options.

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    Dooms101,
    no cost option:
    - to check actual size, i2i and stroke, remove the shock and remove the air sleeve. The shock will be fully extended and offer you the proper measurments. Shock travel would be the exposed 3/8" shaft between the seal head and the eyelet. Disregard the bottom out o-ring.
    - if size is correct and you don't want to spring for a standard sleeve or volume spacers, you can apply incremental mounts of grease in the positive air spring until the spring curve is to your liking. 3-5 CC at a time is probably good.

    If it is a 7.875x2.0 shock W/ an extra volume sleeve, for sure you are rocking a very low air spring ratio.

    I'd suggest an X Fusion RCX for the price and performance, unless you can find the originally spec'd shock for a lower price. From the shock size and bike travel you mentioned, the average leverage ratio of the bike is about 2.3:1. This is on the low side and may still warrant an extra volume sleeve. Hard to tell. Depends on the frame linkage curve.

    Hope this helps.

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    I did what you said and removed the air sleeve and measured the exposed shaft, turns out it is a 2.0 in stroke. So it'll definitely help to at least get the right size.

    The shock I was looking at is a OE 2011 X-Fusion O2 RTZ, here: X Fusion O2 RLZ Rear Shock | Buy Online | ChainReactionCycles.com

    I think it's an OE part made specially for Cannondale. Any idea if this would work well for me? Thanks

  8. #8
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    Quote Originally Posted by Dooms101 View Post
    I did what you said and removed the air sleeve and measured the exposed shaft, turns out it is a 2.0 in stroke. So it'll definitely help to at least get the right size.

    The shock I was looking at is a OE 2011 X-Fusion O2 RTZ, here: X Fusion O2 RLZ Rear Shock | Buy Online | ChainReactionCycles.com

    I think it's an OE part made specially for Cannondale. Any idea if this would work well for me? Thanks
    I realize that's a great price for a rear shock and it will 'work' if it is the correct size. However, the newer designs of the XF O2 RCX and RL are much better, more reliable, and better supported. A '12 would be best. Even a newer '11. Ideally you should ask for their lite tune for either model. OR, a non-boost valve FOX shock would work well too. An older RP3 or RP23. Feel free to message me direct, happy to help. Bad set up is a bad ride and therefore a bad time.

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    So was the boost valve not helping either? The shock I have now has one but I am not really sure what it is does. Is there a good source to read up on for finding the right rear shock? I am going to be using an XF Velvet RL 140mm fork up front so it seemed to make since to go with an x fusion in the rear but I guess it doesn't really matter which brand so much

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    Another method is to add shims/spacers into the air can to take up the extra volume. There are entire threads dedicated to this for people that want to modify the spring curve of their shock. It's a zero cost option, so that's where I would start.
    "Got everything you need?"

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    Quote Originally Posted by TwoHeadsBrewing View Post
    Another method is to add shims/spacers into the air can to take up the extra volume. There are entire threads dedicated to this for people that want to modify the spring curve of their shock. It's a zero cost option, so that's where I would start.
    I know a few people who have gone this route, with great success. If you're not keen on DIY solutions, FOX makes a kit for the RP series shocks. Pinkbike did a how to a while back on it, takes less than 10 minutes to install.

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    I read about the shim method and I would like to try it since it's no-cost but my shock isn't the right stroke to begin with. Is there anyway to modify it so it's a 2.25 in stroke? I know that there's just a spacer kind of thing that makes the difference between the 2.0 and 2.25 stroke models, everything else is similar.

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    Had the same issue with an rp23 with boost valve.

    Look for the Fox Float Air-Volume Spacer Kit on the internet or call around shops. Its 3 pieces of plastic and some blue fox fluid. Also, you can try adding more fox fluid in the canister to take up more space (i just use Cam Guard assembly lube for engines).

    Just gotta try every piece in the kit to figure what is best for you. It took literally 1 minute to install/replace (including time to deflate and inflate shock). Super easy.

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    Quote Originally Posted by Dooms101 View Post
    So was the boost valve not helping either? The shock I have now has one but I am not really sure what it is does. Is there a good source to read up on for finding the right rear shock? I am going to be using an XF Velvet RL 140mm fork up front so it seemed to make since to go with an x fusion in the rear but I guess it doesn't really matter which brand so much
    Read some of the other posts. Yeah, you need the correct size shock. Luckily a 7.875x2.0 is a very popular size. The clip on spacers/shims mentioned for the FOX are great too, if you need to dial in the air spring curve a little more. For FOX shocks though, best not to use the FLOAT Fluid to alter the spring curve because it will likely migrate to the negative chamber through the internal transfer port on the inside of the air sleeve.

    Anyway, not sure how much to tell you about the FOX boost valve on FLOAT shocks. It's their version of the position sensitive damping that came into the mtb world over ten years ago and was made popular by Manitou's SPV and Progressive's CVT. It's not a bad thing. It's FOX's 'new technology' and I think they are finally doing a good job with it. I think they were rushed at first. We shall see if they stick with it. You will do plenty good with a non-boost valve FOX shock or, my suggestiong, match your XF fork with an XF shock.

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    So I guess I am going to look around for another fox float with a normal volume sleeve or a newer x-fusion O2 of the right size. I know that the float I have now has some info on it about the velocity tune. rebound tune, and compression tune;what sort of tune I be looking for when getting a new rear shock?
    Last edited by Dooms101; 01-30-2013 at 08:48 PM.

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    Sounds like a typical fox float shock. They're just flat out poor shocks.

    If you want to solve your issue forever, change shocks. Theres bandaids for floats, but they're just that, bandaids.

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    Quote Originally Posted by One Pivot View Post
    Sounds like a typical fox float shock. They're just flat out poor shocks.

    If you want to solve your issue forever, change shocks. Theres bandaids for floats, but they're just that, bandaids.
    I've only ever used the float so I don't really have any basis for comparison. Why do you say that they suck? Would you recommend a newer xf O2 instead? How about a DHX 5.0 air?

    I found a good deal on a fox DHX 5.0 air of the correct size with a low volume air can on it, seems like it would fit the bill.

  18. #18
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    Quote Originally Posted by One Pivot View Post
    Sounds like a typical fox float shock. They're just flat out poor shocks.

    If you want to solve your issue forever, change shocks. Theres bandaids for floats, but they're just that, bandaids.
    You're saying the entire Float line is garbage? Both my RP2 and RP23 have been great, so maybe I'm super lucky or you've been very unlucky?
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    Just buy a low volume sleeve it will really change the air spring curve & won't break the bank. If after that it still doesn't fit the bill look into a custom tune. Trying to reverse engineer , yourself, the dampning configuration is pointless. Sure there are better shocks available but they will cost $$$. Personally, I'd take an RP23 over a DHX-A.

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    Quote Originally Posted by keen View Post
    Just buy a low volume sleeve it will really change the air spring curve & won't break the bank. If after that it still doesn't fit the bill look into a custom tune. Trying to reverse engineer , yourself, the dampning configuration is pointless. Sure there are better shocks available but they will cost $$$. Personally, I'd take an RP23 over a DHX-A.
    Well I would modify the shock I have now but it's the wrong stoke so I am really just trying to find a new one. I found a reasonably priced RP23 without boost valve, a high compression tune, and the low volume air sleeve so I think it's exactly what I am looking for. The only thing I am unsure about is the high compression tune, will that translate into a better pedaling platform but less small bump compliance? Which is actually what I'd prefer.

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