Jet 9 Alloy -> 27.5+...Good idea?-
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  1. #1
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    Reputation: ColinD's Avatar
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    Aug 2015

    Jet 9 Alloy -> 27.5+...Good idea?

    I have been having a great time on my 2017 Jet 9 Alloy since I bought it several months ago. Great bike. Other than taking 10mm off the bars and adding a dropper it is still stock
    I am 5'7" @ 165-170.
    I ride in and around Austin Tx. (limestone rocks and rocky ledges with some flowy single track...mostly blue trails.
    The frame is a medium, a tiny bit large for me. That's the thing. As I get more confident on this rig the wheels just feel big under me. I am not a "big air"guy but I do leave earth from time to time and I feel like I am wrestling 29s back down. I hope to demo a med RDO soon to confirm my suspicions but I feel the 27+ option might be good for me.

    My questions;
    1. Has anyone done this mod?
    2. 15mm Lower cup change -or- extend the travel on the Yari fork?
    3. What is the smallest dia. tire I can use and still keep BB clearance?
    4. What important question(s) an I not asking?

    Thanks in advance!

  2. #2
    Reputation: UPSed's Avatar
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    Dec 2010
    I have a '17 Jet 9 RDO and I go back and forth between both wheelsets. I actually prefer the 29" wheels for most of my riding. That being said if you try the 27.5+ make sure they are at least as light as your 29" wheelset or you won't feel much difference.

  3. #3
    Chilling out
    Reputation: bear's Avatar
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    Feb 2004

    Have you read this article on this subject by Sonya Looney? Seems relevant to you.

    I have a '17 RIP9RDO and both size wheelsets (Stan's Baron S1 rims for 27.5 and Flow Mk3 for 29).

    I've run tires on the 29er from 2.2 (Maxxis Ardent) through 2.6 (Schwalbe Nobby Nic) girth, my two favorites so far as the Continental 2.4" Trail King/der Baron/der Kaiser "projekt / apex" type (very heavy duty, like 1100g each) and the current 2.6" Addix Nobby Nic (about 970g each).

    I've run tires on the 27.5 from 2.8 (Maxxis Ikon+/Rekon+) to 3.2 (Vee Trax Fatty I think it was) girth. My go-to is Rekon+ 3c front and 2c rear, so far.

    There's about 1/2" of BB drop on my 27.5 vs 29er setup. When swapping the only accommodation I make is a slight change of fork PSI to increase sag a little when running 29er, by no more than 10mm. I have an MRP Ramp Control cartridge in my fork so I don't need to do any internal fiddling to increase progression if I feel the urge.

    ASSUMING your frame and fork will clear the 2.8" tires ...

    To guess if your frame will fit the 2.8" tire setup ... on my bike the Rekon+ on my rims measures 70mm at widest point and about 80mm on the outermost point vs the inner spoke bed - the ERD measurement. So about 644mm diameter based upon the Baron S1 ERD of 564mm.

    Changing the wheel/tire size will also change 'trail' a bit which alters feeling a bit more than just tire rotational weight impact, see S.Looney's writeup please ... I could totally agree with her on that but I'm very adapted to 29er so it's a mostly non issue for me.

    What rims and tires are you running now?

    ... all that spew stated I'd go with increasing the fork travel to adjust the head angle vs fork trail change when going down in wheel size You gain the advantage of more overall fork tuning options, maybe.


    I've found the "feel" of the 29er wheel based bike is so heavily dependent upon the tire/rim choices and how rigid (or not) they are, and how much rolling resistance the tires have. Maybe more so than a smaller wheeled bike. Changing to easier rolling or lighter tires may change things a lot for you.

    Of course, doing that in Austin can be dangerous to your rims. Been there, banged that. :^)

    Good luck.

  4. #4
    mtbr member
    Reputation: ColinD's Avatar
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    Aug 2015
    Thanks for the quick and detailed replies! I read the article and lots of the comments...definitely helped me define my "issue"

    Here in Austin there is a lot of trail that favor a 29" but there is also a growing number of tight, technical, and jumpy options that I really enjoy. This is where my current set up feels cumbersome.
    I have not run the cost on the components for the Yari travel adjustment but I agree, this would be better than the lower cup. I would use the extra travel for sure!
    I am on a married man's budget so I don't really have the luxury of $1000+ wheel sets and going through all kinds of tire options so I really appreciate you (Bear) taking the time to share your preferences. Lots to think about.
    Seems like getting on a 27" medium demo is the next step


  5. #5
    mtbr member
    Reputation: ColinD's Avatar
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    Aug 2015
    Bear, I finally had a moment to give a proper read to your reply...

    My current set up is stock Niner alloy wheels; 110x15 / 148x12 with Maxxis Ardent F60 SC EXO rubber; 2.4 F, 2.25 R
    This is also stock.
    I am a bit of a newbie and don't have a lot of exposure to different set ups but this set up seems to roll well (?) I grew up on BMX (I am pushing 50 yrs old) and I surfed in hawaii my whole adult life (read; In pretty good shape) so I am getting better and more confident pretty quickly. I do notice what seems to be wheel flex when pushing this bike hard.
    Is it maybe my BMX backgroung making these wheels feel big under me? I had an Airborne Goblin hard tail for a year or so before moving to my Niner. It was a 29" and also felt cumbersome at tmes.
    Maybe I am trying to put square blocks in round holes here but this set up does not seem to be taking my riding where I want it to go -or- I need to embrace the benefits of a 29" trail bike and explore that progression....hmmm?
    Here is a short video I made when I first got my Airborne...

    You can see I am already fighting the set up instead of riding the bike in the way it was designed.
    Thank again

  6. #6
    Chilling out
    Reputation: bear's Avatar
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    Feb 2004
    The Ardent tires tend to roll ok, but the Ardent Race rolls better, and the Ikon and Small Block 8 a LOT better, in my experience.

    I'm sure your history of BMX will make the wheels feel big, I know that I always have a bit of adjustment to go through riding my DH or DJ bikes as they're both 26er and I had some adaptation going from 26er to 29er back in 2012. :^)

    I'm not surprised if you feel wheel flex, it's not uncommon for the machine built wheels to not have the highest spoke tension / stiffest build, and again this feeling would be aggravated by your experience on BMX as the smaller radii wheels can be inherently more perceptibly stiff.

    I don't know which specific rims and spokes are on the Niner wheels BUT I would be surprised if they were high-tension spoked Stan's Flow Mk3 or Arch Mk3 rims. ;^)

    No matter what else you do I'd suggest you get with your local wheel guy and have them check the true and tension to make sure you're not getting anything needless from that. If the wheels are still in good shape that should be like a 15 or 30 minute job. If you've the right tools you could do it yourself, hopefully the rims have a sticker describing the max spoke tension they allow.

    If you can find someone with a set of 29er rims/wheels to test (ideally with same tires, with something akin to Flow Mk3 - IMO) that are built more robust (e.g. good even/high spoke tension) you may try them out just because it's an easy swap in and more direct comparison to what you have now. Gotta be somebody in Austin that would work with you on this, just get on bikemojo and holler out (along with the customary beer offering of course).

    I know I never feel like my Flow Mk3 wheels are letting me down, and they've dealt with some hard stuff, I'd throw them against ATX trails any day. ;^)

    Swapping in 27.5 WILL bag notable reduction in the wheels feeling big, even going with 2.8" or 3.0" tires so long as you don't get dirtbag tires, but they WILL also drop the bottom bracket notably as you've noticed. IMO don't even think about using less than a 2.8" tire in that size ... but see if you can try a better built set of 29er wheels first.

    Bottom Line Remote Advice (take as you will)...

    If you want your JET to be ridden more like what you shared in your Goblin video and you can deal with the BB drop (even with fork adjustment one way or the other there will be some) a 27.5 wheelset with ~35mm ID (like the Stan's Baron) and 2.8" tires will probably serve you well. The front of the bike is still going to be feel long for a while just because it is, but it's longer than what you had before. :^) Still, decent rims and spokes and a good build will work well. I hammered the crap out of my 27.5 wheels fall '17 in CO and UT and all over NE PA/NJ/NY and nary an issue (Stan's Baron S1 rims on I9 hubs).

    I do think that for a more wide usage pattern though you'd be best served by the right 29er wheelset, and something hand-built within Flow Mk3 (great durability/weight tradeoff) would be a good example.

    Again, good luck.

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