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  1. #1
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    2013 S works Stumpy HT fork query

    Does anyone know if the factory specced SJ 90mm travel fork can be increased to 100mm like that used on the 2013 S works Epic?

    cheers

  2. #2
    J-Flo
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    Yes. I assume you have the SID Brain fork with single air? There is a 10mm plastic spacer inside the air spring chamber that you can remove to achieve 100mm travel. Go to the SRAM website and hunt around and you will find service instructions on how to take the fork apart properly. The air spring internals are the same as a regular SID with single air. It is not a difficult job but does involve removing the lowers and disassembling the air spring, and you might as well replace all the oil and seals while you are in there. If you are not a DIY type then any decent shop can do this for you.

    I am not sure why you would want to do this, though. The 90mm travel fork is perfect for your bike's geometry. Is another 10mm of travel worth having your bars about 8-9mm taller, which also will make the bike slightly more slack (I would guess at least 0.5 degrees)?

  3. #3
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    @ Jfloren Many thanks for that helpful reply. I actually have a an epic frame with no fork and the only fork I can get hold of in NZ is the stumpy 90mm so was wanting to keep the geometry of the epic. Thanks again

  4. #4
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    I don't see how this effects the geometry as the crown to axle measurement remains the same. I have both the 90mm SID WC 29 w/Brain fork and the 100mm SID XX WC 29 fork and the Axle to Crown Length is 506 mm on both. This spacer just limits the travel when the fork is compressed.

  5. #5
    J-Flo
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    Quote Originally Posted by Dry Side View Post
    I don't see how this effects the geometry as the crown to axle measurement remains the same. I have both the 90mm SID WC 29 w/Brain fork and the 100mm SID XX WC 29 fork and the Axle to Crown Length is 506 mm on both. This spacer just limits the travel when the fork is compressed.
    For the SID dual air forks (as well as all other RockShox, such as Reba and Revelation), the spacer limits how far the air spring shaft can extend. Thus, taking the spacer out allows the fork to extend more, making the fork taller. The spacer does NOT limit the travel at the bottom end, rather it limits the top end.

    If your "90mm" and "100mm" forks are exactly the same total length, if there is actually a difference in the travel then that almost certainly means there are other differences between them. Check to see if they have the same lower leg length; if they do, then my bet is that your two forks actually have the same travel, unless they have some other design difference. Check it out -- do they have the same amount of stanchion exposed? If so, the travel on your two forks is actually the same.

    Think about it -- it would not make sense to use a spacer to limit travel when the fork is compressed. Why would anyone do that? That's why a 90mm fork has about 10mm less stanchion exposed than a 100mm fork. The point of the spacer is to control the overall length of the fork, so you can get the front end down low.

    I just checked and note that the design has changed with the 2013 Solo Air forks. According to the manual, the 2013 SID no longer uses a spacer for travel adjustment. Instead, now you need to buy a new air spring assembly in order to change travel.

  6. #6
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    Thanks for the explanation. Yes the forks appear identical in all measurements. The 90mm came on a 2013 Stump Jumper S-Works XTR and the 100mm I put on a Niner Air 9 Carbon single speed. The local Specialized dealer did tell me what you found about needing a new air spring assembly to get 100mm of travel instead of just removing a spacer. I ordered the kit so I shall see what changes with the installation of the kit. I am actually hoping for just slightly slacker geometry to bring the S-Works consistent with the Niner A9C geometry.

  7. #7
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    I stand corrected on the measurements. With the forks in neutral position (no load) the amount of exposed upper tubes measured as follows:

    RockShox SID XX World Cup: 3.8 inches / 96.52 mm
    S-Works SID WC 29 w/Brain: 3.625 inches / 92.07 mm

    So while not a 10mm difference, there is some, so hopefully the new air spring will slightly lengthen the SID WC 29 w/Brain giving the Stump Jumper a tad more relaxed front end.

  8. #8
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    Yes,as said before it is easy to do but why not just leave it.I got HT and epic and have converted the epic fork down to 90mm just like the HT.Never felt i needed or missed the 10mm and the bike does feel better.Many of the Spez pro riders have done the same.

  9. #9
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    To each his own. I like the slightly slacker 71 degree HA on my Niner A9C w/100mm.

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