How do I select the appropriate Gears for a build?- Mtbr.com
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  1. #1
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    How do I select the appropriate Gears for a build?

    I'm building a fat bike off of a Gravity Knockout 14" Frame that my nephew can ride as well as friends/family when they come over and want to go for a ride with the us.

    anyhow; I bought an FSA Platinum DH BB and a Crankset that was a new/takeoff from an origin8 Crawler off ebay.

    The Cranks are 170mm with a 32tooth chain ring.

    I've already got the wheelsets completed, but now I need to figure out what cassette to buy for the rear wheel and have NO idea what I'm doing. It's for sure going to be a 1x? drivetrain; but for simple cruising around on flat terrain and riding down the beach, how to I figure out what will be an easy to ride set of gears? I think I'm limited to a 7 speed cassette, but I'm not sure of that either.

    What needs to be my first step in selecting a cassette?

  2. #2
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    Based on chain ring and hub figure out how many speeds you can have. Then buy a cassette with that number of speeds with the largest number of teeth possible.
    For sand crawling with people who don't bike much the lower the gear the better.
    So basically if you have an 11-32 option or 11-34.. Go with the 34

  3. #3
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    The wheels are the same wheels that J&B Use on their Sun Crushers/Baja Cruisers and are 80mm wide.

    I had my LBS lace them up with Origin8 hubs. I'm entirely new to doing anything like this; so please excuse my complete ignorance. I'm trying to learn as I go further with the build w/o making mistakes such as ordering incompatible hardware.


  4. #4
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    For sure get a cassette with the biggest rear cog. You can get a 12-36 9 speed cassette relatively cheaply. Even if you have to put a thin spacer behind it, and leave one of the smaller cogs off, its probably your best bet. Especially on a loaner bike, where the rider will need to low gears.

  5. #5
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    The Orgin8 fat bike hubs are 8-9-10 speed compatible - not a 7 speed hub. 9 speeds gives you lots of cassette and shifter options without breaking the bank. 8 speed stuff is hard to find anymore. :-)

  6. #6
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    7 speed cassette would probably need a spacer. 8 speed still uses a cheap chain and, well, cheap everything. You should be able to do 32 or 34 teeth in low which will really help.

  7. #7
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    If it's 8-9-10 speed compatible then either nine or ten. I have built both recently with a 1x and honestly you don't save much by going 9.
    SRAM x5 or shimano deore level cassette and shifter/ derailer can probably be done for $100 or under with an 11-34 or 11-36, I can't remember if they m make 11-36 though.

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    30x19.

  9. #9
    beer thief
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    simple1 has the right idea. Most of you guys seem to have missed the "cruising around on flat terrain and riding down the beach" part of the post. Even riding in soft sand does not require very low gears. A 30 or 32 chain ring with a cassette up to 32 tooth should work fine for anyone in the terrain described.

  10. #10
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    Ya'll have been a tremendous help thus far...

    so I'm currently looking at the:

    SRAM X9 Type 2 Long Cage Derailleur (Or possibly one of the X0's that I'm watching on ebay)

    SRAM X9 Trigger Shifter

    SRAM PG-1050 (either then 11-32 or the 12-36 as I'm not sure yet)


    (I upgraded my Origin8 Cralwer to Avid Titanium levers and I'm going to use the stock Avid Speed Dial 7s on this bike. I also ordered a set of BB7 calipers & 160mm rotor for the rear and 180mm rotor for the front.)

  11. #11
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    Right on the main page of the site this morning there was a sponsor ad for a SLX groupset. Many retailers offer this. If you're not sure the compatibility, ordering a complete drivetrain box of parts might best. At a minimum you can read the specs of the bits included to build your own.

    To keep it simple the first time around you should use same brand shifters and derailleurs. Other than that the rest of the components can be mixed across brands.

  12. #12
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    Quote Originally Posted by radair View Post
    simple1 has the right idea. Most of you guys seem to have missed the "cruising around on flat terrain and riding down the beach" part of the post. Even riding in soft sand does not require very low gears. A 30 or 32 chain ring with a cassette up to 32 tooth should work fine for anyone in the terrain described.
    Some people riding the bike might have no biking experience. If you're going to have an 11-32, why not just get an 11-36 when that might help someone who isn't strong or fit?

  13. #13
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    why long cage?

    I'm trying to figure out which bike you're trying to equip for this post. I agree that for a cruiser bike, you don't need a huge range in gearing. I agree that 32t max cassette would be more than adequate. Exactly what rear hub do you have? If you're talking about the middle bike in that pic, it looks to me like a freewheel hub and not a cassette hub.

    Better pics and links to exact components would be helpful.

  14. #14
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    How do I select the appropriate Gears for a build?

    I've looked at some of those group sets and I've found them to be cost prohibitive based on having items I don't need, all I need is a cassette, rear derailuer, and shifter.
    The hub on the rear is a Origin8 170mm hub that J&B laced into that wheel (my LBS coordinated getting it done)


    The bike I'm building is the center one. It's a Gravity Knockout frame ( $150 from bike island) and I've used my spare parts and upgraded takeoffs from that Crusher & Crawler.

    My goal has been to build it up with better than average parts (many from Amazon Warehouse Deals) keeping as cheap as possible but better quality than a big box fat bike.

  15. #15
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    Here's a few pics I just took of what I've got so far.

    This is the hub, an Origin8 170mm Hub



    Chainline (which I have NO way of measuring to know what'll fit and what wont fit).








    Bottom Bracket is an FSA Platinum DH (same BB that is on my Origin8 Crawler)




    Crankset are new takeoff's that I scored off ebay for like 25 dollars that came off an Origin8 Crawler as well.







    And I'm going with these Origin8 Captiv8or UL 26x3.5 tires..they're TIGHT on clearance in this picture, but they'll roll w/o hitting the chain stays.


  16. #16
    Two Headed Boy
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    I was considering building one up for my son, would a 3.8 knard clear in the back?
    tSETFREEBYLOVEt

  17. #17
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    Quote Originally Posted by Trower View Post
    I was considering building one up for my son, would a 3.8 knard clear in the back?
    nope....the 3.5 BARELY clears....the only way a 3.8 *MAY* clear would be to use narrower wheels...but no way on 80mm wheels like i've got on this frame.

  18. #18
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    How do I select the appropriate Gears for a build?

    The bike is coming along


    Is there a big difference between an 11 & 12 tooth gears when using a 32tooth up front?


    I can't figure out wether to go 32 or 36 tooth for the big sprocket either.

  19. #19
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    Quote Originally Posted by shank3r View Post
    The bike is coming along


    Is there a big difference between an 11 & 12 tooth gears when using a 32tooth up front?


    I can't figure out wether to go 32 or 36 tooth for the big sprocket either.
    11 will give you a slightly higher gear. Maybe useful if you have to ride to/from the beach on the road very far.
    Some people like 12 because they don't care about having a faster top gear, but it makes the progression from cog to cog slightly smoother.
    32 or 36 is preference.
    36 will give you a much lower low.
    36 will also give you bigger jumps on some of the gear changes though, which can occasionally be annoying.

  20. #20
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    I ended up getting a:
    SRAM X7 type 2.1 dérailleur
    SRAM X9 trigger shifter
    SRAM PG1050 12-27 cassette with a KMC X10.93 chain

    Even though I don't have brakes yet (I scored an Elixir 9 trail with 203mm rotor off Amazon Warehouse deals for cheap but missing a few items) I put my seat & pedals off my Crawler on it and went for a ride. I have a feeling that the 12-27 cassette will suit the needs of this bike nicely on our flat terrain. I kinda like the fact that it has a narrow gear selection and the 27T cog on the low end should be plenty for the very small climbing around here now my wife should be able to go on distance rides with me. (She has a Sun Crusher single speed and it's not quite up to the task of keeping up with me on my Crawler when I go for long rides)...but her Sun Crusher is the ULTIMATE cruiser..its buttery smooth and an easy going kind of bike.

    The known defect of these bikes is that the chain rubs the dropout on the smallest cog. I think I can put a 2-3mm spacer between the hub/dropout and fix that w/o a problem.


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