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  1. #1
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    New question here. Chain ring Upgrade - 28T to 34T for SRAM NX

    Hello MTBR members!

    I have a question about my speeding up my ride. Recently I purchased a bike (a Giant Fathom 29er 1 to be exact) after having my previous precious Giant 2008 Yukon stolen.

    I often go riding in the bush but most of the time I use it to commute to work. I realised that it goes pretty slow on the road, topping and spinning out at 27 km/hr (16.78 mph) which is pretty kinda slow.

    The Yukon I rode in the past can easily achieve 45 km/hr (27 mph) on flat ground in which I struggle with the Fathom 1.

    I went to the bike store which is located (1 hour away from my home) to quote to change the chain ring to 34T (currently 28T). Over the phone, he told me that I need to change to a:
    - SRAM X-Sync BB30 34T
    - SRAM X-Sync Spider 104PCD


    I do not have a clue what goes with what. And apparently I also need to change the chain. The total charge will be around $250.

    I have three questions (for now):
    1. Which parts are they referring to? Can someone link me the item that will suit my bike?
    2. Which one is the chain for the 34T recommended?
    3. What kind of tools will I need to buy to replace it myself?

    Thanks in advance!

    Chain ring Upgrade - 28T to 34T for SRAM NX-img_20170705_171752.jpgChain ring Upgrade - 28T to 34T for SRAM NX-fathom-29-1-blue.jpg
    D.Xenotime

  2. #2
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    You spin out at 80 rpm? A 34 tooth chainring will have you going 33-34 km/hr at the same 80 rpm. You won't get the same range with your current 1x setup as your previous 3x drivetrain on your old bike. Switching to 34 might be worth it to you, but keep in mind your low gear won't be as low either. It will be 21% higher than before.

    It looks like that OEM SRAM NX crankset, unlike the aftermarket ones, uses a direct mount chainring. Unless I'm missing something, you should be able to just get a SRAM direct mount chainring and just directly swap that out:

    https://www.sram.com/sram/mountain/p...8ws81lzpssuyz8

    Take a close look at the mounting pattern of your current chainring, looking from the back side of the cranset. If it matches he chainrings in that link I provided, that's what you need. The bike shop is suggesting that you buy a chainring that bolts onto a 104 mm bolt circle diameter 4-arm spider, plus a 4-arm spider that fits onto that SRAM direct mount. That would work, but staying with the direct mount ring would be better and cheaper.

    There's no special chain for 34 tooth chainrings. You need a new chain only because the chain will be too short after you switch chainrings from 28 tooth to 34 tooth.

  3. #3
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    Add: The Giant website says you have a GXP bottom bracket, so you'll probably need a direct mount chainring for a 24 mm spindle rather than a 30 mm spindle (which is the BB30 type). That note from your bike shop for BB30 confuses me. Make sure you figure out what you have. There's also 2 different chainlines. Pretty sure you have standard chainline, as opposed to BOOST.

    https://sram-cdn-pull-zone-gsdesign....ity_160111.pdf

    Tools needed are just hex wrenches or hex bits along with a torque wrench.

  4. #4
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    https://www.sram.com/sram/mountain/p...qcpn4djgguyqfq
    It looks to me like that crankset uses direct mount chainrings. A spider is a mounting piece for the chainring, which direct mount don't use. BB30 is a bottom bracket I believe, which I don't think you need.
    It looks like you should just need a new chainring and the labor to swap it out. I would go to youtube and try searching for "how to swap out sram chainrings". It is likely very easy and cheaper to just buy the tools and do it yourself if you feel like you are at all handy with tools.
    Around 30 bucks for the chainring, plus the tools.

  5. #5
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    I'm not saying that you shouldn't get a bigger chainring but if you really want to go faster you should work on your cadence because you should easily be able to average over 20mph with the gearing you have @ 90-100rpm, which is pretty much optimal efficiency.

    When I say easily I mean cadence wise though, very few people are strong enough to average 20mph on a mountain bike (flat ground) no matter what size chainring they have.
    I brake for stinkbugs

  6. #6
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    I brake for stinkbugs

  7. #7
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    If you can easily achieve 27mph on an mtb on flat ground, you could probably go as big as 38 or 39 up front. You should be racing too, you would do well.
    I would look at a new crank/chainring combo on ebay. Look at your bottom bracket markings for what type you have, and the crank, to check compatibility.
    Yes, you would need a new chain; the old chain would likely not be long enough for the big gear in back, with the bigger gear in front.
    carry clippers! cut something off the trail every time you ride.

  8. #8
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    readjust your meter from 26 to 29 in?
    switch tire?
    usually 32 is enough

  9. #9
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    Quote Originally Posted by Len Baird View Post
    ...it looks like you should just need a new chainring and the labor to swap it out. I would go to youtube and try searching for "how to swap out sram chainrings"...
    Thank you so much LenBaird~ I did a Google search as you recommended and landed on this Youtube which I find it very informative. What about chains? Which model of chain should I purchase to go along with the 34T version? Many thanks for the advice. https://www.youtube.com/watch?v=bO5SaLkRhO0

    Quote Originally Posted by xcandrew View Post
    Add: The Giant website says you have a GXP bottom bracket, so you'll probably need a direct mount chainring for a 24 mm spindle..
    Thank you XCAndrew for the response. Can you explain to me more about what is the 24 mm Spindle you talking about? I am not too familiar with this term or which parts you referring to.

    Quote Originally Posted by J.B. Weld View Post
    … you should work on your cadence because you should easily be able to average over 20mph with the gearing you have @ 90-100rpm, which is pretty much optimal efficiency. When I say easily I mean cadence wise though, very few people are strong enough to average 20mph on a mountain bike (flat ground) no matter what size chainring they have.
    Hello J.B. Weld. Sorry for the late response. I was fairly busy with work and did not have a time to look into detail with the responses I got. I do not have a cadence speed meter thus unable to measure how fast I was pedalling. My need is basically to ride faster. Back on my Yukon, it was not ‘spinning’ out when I was riding on the road and I could cruise perfectly without spinning out at 21 mph (around 35 km/hr). Since the new bike has less teeth, this is what prompt me to ask what parts I need to buy.
    D.Xenotime

  10. #10
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    Quote Originally Posted by 33red View Post
    readjust your meter from 26 to 29 in?
    switch tire? ... usually 32 is enough
    I double checked my Cateye bike computer to make sure that it is at the correct settings. It is as checked set on a 29" wheel.

    I am not sure what unit is your 32 referring to. I am trying to achieve 32 km/hr cruise ride without spinning out which I am right now on 28T chainring.
    D.Xenotime

  11. #11
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    Quote Originally Posted by Xenotime View Post
    I double checked my Cateye bike computer to make sure that it is at the correct settings. It is as checked set on a 29" wheel.

    I am not sure what unit is your 32 referring to. I am trying to achieve 32 km/hr cruise ride without spinning out which I am right now on 28T chainring.
    My 32 was the teeth number for your chain ring, well i am on 11 speeds SRAM 10-42 maybe you are on Shimano with an 11 teeth,, i only have a 9$ watch but it has a stopwatch, i can count 15 or 20 sec times my right pedal is down, multiply by 4 or 3 and know my cadence wich is RPM or rotation per minute, practice about 90 and about 100. We are all different for me spinning is easy(fast cadence) so occasionally i train max effort about 55 RPM but i guess you are better than me on the power side, my strong natural side is endurance.

  12. #12
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    Just putting this out there... But have you thought about a more road oriented bike if your upgrading purely for commuting? I mean your trying to change a 1x setup MTB for faster flat road use?

    For a few hundred more than the shop is charging, you could grab a cheap urban flat bar style bike. Such as a trek urban/hybrid or even gravel style road bike with 32mm tires which will be comfortable and fine on gravel. It will cruise better, be lighter, have road tires and be better geared for cruising at ~ 30kmh. Then just use your MTB offroad.

    I have something like that to get me to the station as part of my commute then I'm not wearing my MTB tires out of road surfaces. Just food for thought :-)

  13. #13
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    Quote Originally Posted by wired00 View Post
    ...For a few hundred more than the shop is charging, you could grab a cheap urban flat bar style bike. Such as a trek urban/hybrid or even gravel style road bike with 32mm tires which will be comfortable and fine on gravel. It will cruise better, be lighter, have road tires and be better geared for cruising at ~ 30kmh. Then just use your MTB offroad...Just food for thought :-)
    I appreciate this though. I am kinda jungling between wallet vs space in my apartment. I would absolutely love to have the space to buy and store two bikes~!
    D.Xenotime

  14. #14
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    Quote Originally Posted by Xenotime View Post
    I appreciate this though. I am kinda jungling between wallet vs space in my apartment. I would absolutely love to have the space to buy and store two bikes~!
    Ahh yep completely understand :-)

  15. #15
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    I have the spider with 32T X-Sync chainring that originally came with a GX1400 crankset, and isn't serving any purpose. It was used for maybe 50 miles, since I almost immediately replaced it with a direct mount oval. If that'll work with this crankset...well, just PM me your mailing address.

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