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  1. #1
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    Foes/Curnutt vs RP23

    Thought this might be of interest to some...

    Been riding an XCT-5 for a couple of years with the Foes/Curnutt XTD Air shock and have been happy with the performance for my XC riding style on a wide variety of terrain. Had the opportunity to pick up a new RP23 with the updated boost valve (uses the same licensed SPV patent as the Foes/Curnutt shock) for next to nothing, so I went ahead and gave it a try along with the Foes adapter. I'm not up to speed on all of Fox's tunes and such, but the stickers on the shock say "boost valve tune 175, velocity tune M, rebound tune M". After playing around with the adjustments some, I settled in on 200 lbs in the air chamber (I'm not svelte), rebound about 3 clicks out, and boost valve on 3. Been on a couple of rides now, one in Phx Mtn Preserves (220, fenceline, 8/8A, 304, 1A, 100), and one up in Flag (Shultz, Climb 3, Sunset, Shultz).

    I hate to say it, but I like the bike better with the RP23, and not by a small amount. The bike is noticeably smoother in every situation. Downhills are really plush with the pro-pedal set to open. With pro-pedal engaged, the ride is still much smoother than the XTD ever was. It's nice to be able to switch the platform on and off. The only downside is that the rock-solid pedaling performance of the XTD is definitely compromised, even with the pro-pedal on the highest setting (3). Most of the time that's not a big deal for me since I'm usually not in a hurry, but I could see it being an issue for someone who's looking for the best efficiency while climbing. The one thing I don't know about yet is bottoming control. The XTD could be run at low spring pressures and still provide perfect bottoming control (in fact I never felt the bike bottom in 2+ years even though it was using all its travel). I haven't really bombed into anything big yet with the RP23, so I can't comment on how it will control in that situation.

    Next step for me will be to check and see if any other tunes are available for the RP23 that might firm up the platform just a little bit. I will also likely send the XTD back to Foes to get it rebuilt (secondary chamber has been leaking) and see if they can detune it some to soften up the response a little to make it more like the RP23. Something inbetween the two would be ideal for me, but for now the RP23 will be staying on the bike.

    Cheers,
    -Brian

  2. #2
    Elitest thrill junkie
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    You can definitely get the RP23 pushed, to tune it better to your weight/style/bike, or go with a different volume air can (if necessary). Anti-bottoming, platform, oil flow, and damping in general can all be improved.
    "It's only when you stand over it, you know, when you physically stand over the bike, that then you say 'hey, I don't have much stand over height', you know"-T. Ellsworth

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  3. #3
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    I sent an email off to Fox to see what their "Pro Tune" service can do. I'll check with Push as well. Good thing we got such a good deal on the shock if I'm going to have to spend another wad of cash to make it work right. Or maybe I'll just stop complaining and go ride!

  4. #4
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    I'm not surprised tbh. Although few shocks can match Curnutt in terms of pedalling performance, I think most modern shocks have exceeded them in terms of plushness / control. ... they don't have the advantage they once did.

  5. #5
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    Quote Originally Posted by azoutside
    I sent an email off to Fox to see what their "Pro Tune" service can do. I'll check with Push as well. Good thing we got such a good deal on the shock if I'm going to have to spend another wad of cash to make it work right. Or maybe I'll just stop complaining and go ride!
    Push's services/abilities far exceed those of Fox.
    "It's only when you stand over it, you know, when you physically stand over the bike, that then you say 'hey, I don't have much stand over height', you know"-T. Ellsworth

    You're turning black metallic.

  6. #6
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    Ok so I found a place where the RP23 failed me - Bombing down Shultz, big dip/wash crossing that I'm used to hitting at warp speed with the Curnutt... Bike bottomed hard and spit me off, oopsie, that hurt...

    From my original post, the boost valve tune has been increased from 175 to 200, which is better. Still doesn't have the bottoming control of the Foes/Curnutt though.

    I'm more careful now.
    - Brian

  7. #7
    Eff U Gee Em
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    What is the weight difference

    between the Curnutt and the Fox with adapter?

    Does the Fox have the same stroke or does the adapter somehow (via changing the angle) modify the leverage ratio?

    How does the small bump sensitivity/compliance compare between the 2 shocks?

    Thanks

  8. #8
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    Quote Originally Posted by howdyhowdyhowdy
    between the Curnutt and the Fox with adapter?

    Does the Fox have the same stroke or does the adapter somehow (via changing the angle) modify the leverage ratio?

    How does the small bump sensitivity/compliance compare between the 2 shocks?

    Thanks
    Yes the RP23 has 2.5" stroke, same as the Foes/Curnutt that came with the bike. The shock is physically shorter, so Foes supplies an adapter that slips over the rod end of the shock and bolts to the frame as well as the shock eye. The angles and geometry are unchanged.

    As compared to the Foes/Curnutt tune that came with the bike, this RP23 has much better small bump sensitivity, which leads to a noticeably "smoother" ride most of the time. The tradeoff comes with a degradation of pedaling performance ("platform") and big hit bottoming control. I have not yet sent my original shock back to Brent to see if it can be tuned to provide a compromise between the two, but I don't see any reason why this would not be possible.

    Hope that helps.

    - Brian

  9. #9
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    Quote Originally Posted by azoutside
    Yes the RP23 has 2.5" stroke, same as the Foes/Curnutt that came with the bike. The shock is physically shorter, so Foes supplies an adapter that slips over the rod end of the shock and bolts to the frame as well as the shock eye. The angles and geometry are unchanged.

    As compared to the Foes/Curnutt tune that came with the bike, this RP23 has much better small bump sensitivity, which leads to a noticeably "smoother" ride most of the time. The tradeoff comes with a degradation of pedaling performance ("platform") and big hit bottoming control. I have not yet sent my original shock back to Brent to see if it can be tuned to provide a compromise between the two, but I don't see any reason why this would not be possible.

    Hope that helps.

    I just put my Curnutt Air back on my FXR after having ridden it with a DHX coil for the last 6 months.

    Foes are simply meant for Curnutt shocks. The spring curve of the Curnutts match the Foes perfectly - the Fox spring curve didn't match. You won't be able to get proper sag and progression out of a Fox.
    Stupid, but sometimes witty. Occasionally brilliant. Slow and fat though.

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  10. #10
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    Quote Originally Posted by iheartbicycles
    I just put my Curnutt Air back on my FXR after having ridden it with a DHX coil for the last 6 months.

    Foes are simply meant for Curnutt shocks. The spring curve of the Curnutts match the Foes perfectly - the Fox spring curve didn't match. You won't be able to get proper sag and progression out of a Fox.
    I agree, the bikes work well with the Curnutts on them. To be a little more precise, it's actually the compression damping curve that makes the Curnutt shock what it is, not the spring curve. Pretty much a spring is a spring is a spring, but the real magic comes with the valving...
    - Brian

  11. #11
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    Quote Originally Posted by azoutside
    Ok so I found a place where the RP23 failed me - Bombing down Shultz, big dip/wash crossing that I'm used to hitting at warp speed with the Curnutt... Bike bottomed hard and spit me off, oopsie, that hurt...

    From my original post, the boost valve tune has been increased from 175 to 200, which is better. Still doesn't have the bottoming control of the Foes/Curnutt though.

    I'm more careful now.
    How do you change boos valve tune?

  12. #12
    Indonesian Biker
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    Its good for my reading...sorry for my noobness resurrecting old thread...just for my knowledge

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