2018 Niner Jet 9 RDO 29 with 120 front fork- Mtbr.com
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  1. #1
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    2018 Niner Jet 9 RDO 29 with 120 front fork

    Hey Niner Gang,

    Iím thinking of a new 2018 Jet RDO and using a 120 mm Fox fork with it instead of the recommended 130-140 fork travel options. Do you guys think that will make it feel too much like a ďstink bugĒ with the 10mm dropped front end? I want the 120 mm of rear travel but still make it a touch more capable climber and usable for XC terrain. Am I over thinking this or is it just a bad idea?
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  2. #2
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    Quote Originally Posted by 1-bar View Post
    Hey Niner Gang,

    Iím thinking of a new 2018 Jet RDO and using a 120 mm Fox fork with it instead of the recommended 130-140 fork travel options. Do you guys think that will make it feel too much like a ďstink bugĒ with the 10mm dropped front end? I want the 120 mm of rear travel but still make it a touch more capable climber and usable for XC terrain. Am I over thinking this or is it just a bad idea?
    Kind of doubt it would be an problem, there is at least on guy running a new rip9 with a short fork and he apparently likes it a lot that way. He wanted more #trailbike less #enduro feel, as I recall.



    Sent from my SM-T700 using Tapatalk

  3. #3
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    I have mine set up with a 140mm and feel like it is perfect for XC and trail riding. Climbs fine, but feels different at first, you have to move a little more forward on the saddle to keep the front end down. I would recommend going with a 130 as it is designed for that. IMO 120 would leave the front end and BB too low.

  4. #4
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    I have to agree. 120 would make your BB too low. Unless your riding a bike path. I Run 140mm with my 27.5+ for trail. And 130mm with 29 wheels for XC

  5. #5
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    I am interested in this as well. I have been thinking about picking up a Jet9 frame (competitive cyclist has them super cheap right now) and building it out with a 120mm fork. The idea being to use it as a more burly XC bike. Im 225 lbs and generally find XC specific bikes to be noodly under my weight.

    I *think* I would really like the geo with the shorter front end, I think it will steepen the head angle and the seat angle, by prob .5 to 1 deg. At 68 and 75 deg respectively I think this thing will be primo as a big mans XC racer. (Im sure it would be fine with a 130 fork as well, but I am spitballing)

    Looking at the numbers on some other 29ers in this category (and some out of category) Im not so convinced that running the Jet9 with a 120 fork would put the BB too low. In fact with a 120 fork the Jet9 still seems to be right in the mix BB Height / Drop wise.


    Here is some of the back of the napkin math I have done:

    Assuming a consistent 370mm 29er hub height.
    &
    Assuming that the bb will lower by an amount that is directly proportional to suspension travel (not sure if this is true across all bikes)
    &
    Assuming that (Fork Travel + Rear Travel) / 2 = roughly the amount that a BB will drop when a bike has non equal travel front and rear. (again not sure if this is a vaiid assumption)

    Jet9 @ 130mm Fork
    - 28mm (bb drop)
    Height 342mm (bb height at 0% suspension compression)
    Low 217mm (lowest BB can go at 100% suspension compression)

    Pedal Height 167mm (pedal height with the 175 crank arm in the bottom of the stroke, with the BB at its resting max height)

    Pedal Low 42mm (pedal lowest possible point with the suspension fully compressed and the crank and the bottom of the stroke)


    Jet 9 @ 120mm
    - 32 (bb drop)
    Height 338
    Low 218
    Pedal High 163
    Pedal Low 43

    RKT9 @ 120
    - 28 bb drop
    Height 342
    Low 237
    Pedal High 167
    Pedal Low 62

    Rkt9 @ 100
    - 35 bb drop
    Height 335
    Low 240
    Pedal High 160
    Pedal Low 65

    SB100 @ 120
    - 37 bb drop
    Height 333
    Low 223
    Pedal High 158
    Pedal Low 48

    SB4.5 @140
    - 37 bb drop
    Height 333
    Low 206
    Pedal High 158
    Pedal Low 58

    Blur @ 100
    - 45 bb drop
    Height 325
    Low 225
    Pedal High 150
    Pedal Low 50

    TallBoy @ 120
    - 40 bb drop
    Height 330
    Low 215
    Pedal High 155
    Pedal Low 40

    Capra29 @ 170 - High mode with 170mm cranks
    - 15 bb drop
    Height 355
    Low 185
    Pedal High 185
    Pedal Low 15

    Jeffsey29 @ 140 - High mode
    - 24 bb drop
    Height 346
    Low 206
    Pedal High 171
    Pedal Low 31


    Its interesting to do the numbers like this because you really see that 'Long Low Slack' theme in some of the brands (Yeit, YT). Its crazy to think that at full compression with the pedal down you would only be 15mm away from the ground on a Capra - granted thats very unlikely to happen, just food for thought.

    The Jet 9 with a 120 fork seems to be right in the mix to me. There are bikes out there that run lower. The Tallboy is a prime example.

    Im not saying that you wont ever encounter pedal strikes, just that as compared to other bikes it wont be disproportionate.
    Last edited by howaminotme; 05-17-2018 at 04:33 PM.

  6. #6
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    Interesting analysis and I would agree, itís inline in the current realm of bikes w B.B. height. The J9 can easily be adapted to more trail or more XC based on the fork. I was also looking at the COmp Cyclist deal on the Jet but I ended up going w a Scott Spark RC. Let us know if you do put a 120 on a J9.

  7. #7
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    Also for what its worth I emailed Niner about this and their response was:

    "A 120mm fork on that frame should work just fine. It was actually designed for use with a 120mm."

    Sounds like it should be fine.

  8. #8
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    I called Niner to ask them and the guy was hesitant to say it was ok citing B.B. drop and being like a stink bug. I couldnít imagine 10mm making that much of a difference if the goal is to make the Jet more XC friendly.

  9. #9
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    Canít the Fox 34 be changed between 120mm and 150mm by swapping out the air shaft? I changed mine from 130mm to 140mm. Cost me 50 bucks.

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