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bmx cog on full sized bike

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bmx cog on full sized bike

Old 10-23-08, 01:02 PM
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.jrmyrmx
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bmx cog on full sized bike

i come from a bmx scene and i like like look of a really small chainring/cog. could i weld an 8 tooth driver on my fixie hub and use a really small chainring (keeping the same ratio). would there be any problems with doing this?

thanks,
jeremy
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Old 10-23-08, 01:06 PM
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gestalt assault
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just get a 13t cog...it'll look tiny with a 700c wheel...12t and the chain will be resting on the lockring already...
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Old 10-23-08, 01:07 PM
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blamire
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yep the cog will be too wide
that's why flip flop hubs are dished on the freewheel side.

EDIT: are we talking fixed sprocket or free wheel?
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Old 10-23-08, 01:18 PM
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its a fixed gear hub. ill examine the hub when i get home, ive got an 8t driver on my bmx bike so ill compare it and see how small i can go. if i keep the ratio the same will the ride be the same?
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Old 10-23-08, 01:21 PM
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no because of how geometrically different a fixed gear is to a bmx.
a freewheel will not fit on a fixed gear hub.
slap me if it does.
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Old 10-23-08, 01:25 PM
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a 1:1 ratio is basically like walking...your rear wheel spins at exactly the same speed your legs spin...artistic bikes are set up this way...you wouldn't go very fast on flatland...and if you ever go downhill your legs would look like the Roadrunner's...but if you're making a bike that's strictly for flatland tricks you'll be fine...
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Old 10-23-08, 01:38 PM
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.jrmyrmx
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if i make the cog smaller and then make the chainring smaller by the same increment it will ride the same way as when it was bigger. the only problem would be fitting the cog on the hub and chain rub.
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Old 10-23-08, 01:45 PM
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i think i get what you're saying...you mean do you get the same number of gear inches if you shrink the ratio by the same number of teeth (i.e. 48x16 to a 47x15)...

the answer is no...read the Gearing Primer https://www.bikeforums.net/singlespeed-fixed-gear/468351-gearing-primer.html
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Old 10-23-08, 01:48 PM
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.jrmyrmx
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i dont know the technicalities but i know that a bmx bike with a 8t driver and a really small chainwheel can ride exactly like one with a giant chainwheel if you get the right numbers
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Old 10-23-08, 01:55 PM
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wait...are we talking about making a fixed gear bmx bike here or are you talking about putting a bmx cog on a track bike?
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Old 10-23-08, 01:57 PM
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not a fixed gear bmx, a small bmx like cog on a track bike so i can use a small (26-32t) chainring.
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Old 10-23-08, 02:15 PM
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i guarantee that if you get a 32t chainring and a 12t track cog that you won't be able to see the cog at all...it'll be completely covered by the chain and the lockring...it'll look like the chain is driving the hub itself except for the few teeth poking out the front of the cog where there is no chain...even 39t chainrings look tiny to me on track bikes...plus it'll save you the trouble of welding a cog and ruining a perfectly good track hub...
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Old 10-23-08, 02:31 PM
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I put a bmx cog on one of my mtb's that I made into a ss.
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Old 10-23-08, 02:35 PM
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keep in mind that the larger tire will repuire a different gear ration to get the same gear inches as you have on the bmx
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Old 10-23-08, 03:58 PM
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It's incredibly difficult (I've heard impossible, but I DOUBT it's that) to weld aluminum to steel (or titanium, as might be the case with your 8t DRIVER (Note: drivers and cogs are not the same).

It won't work UNLESS you have a Profile cassette hub and one of the new Profile 1 piece drivers that are both RHD and LHD compatible. If that's the case, you can just flip two of the pawls to LHD while keeping two at RHD, and thereby "fixing" the 8t driver. Doing this will probably work for a time, but will almost definitely cause your engagement ring (LOLOLOLOL) to undo itself from the shell, unless it's a press fit engagement ring, in which case I have no idea what happens. Keep in mind that Profile hubs are spaced 110mm, not 120mm like your fixed hub is spaced, so you'll have to use washers on the inside of the dropouts accordingly.

Try it and tell us what happens?

Last edited by Slavic; 10-23-08 at 04:03 PM.
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Old 10-23-08, 07:29 PM
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god, BMX kids are stupid.
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Old 10-23-08, 07:33 PM
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Originally Posted by jitensha! View Post
god, BMX kids are stupid.
ain't that the truth! gb2/bmx forums
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Old 10-23-08, 09:54 PM
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whatever man, at least im not spending $1500 on a single speed bike like many others on here.

ill probably go with a 12t cog to make it easy.
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Old 10-23-08, 10:16 PM
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Originally Posted by .jrmyrmx View Post
whatever man, at least im not spending $1500 on a single speed bike like many others on here.

ill probably go with a 12t cog to make it easy.
how old are you man? there's nothing wrong with spending your hard earned disposable income and indulging in a one of a kind custom bike...plus it helps support independent frame builders...
sure it's satisfying to ride a bike that you personally built...but it's just as, if not more satisfying to ride a bike that was custom tailored to your specifications by a person who has mastered the art of frame building...
it's like in Kill Bill where Uma Thurman goes to Hattori Hanzo to make her a katana...
now $800 for a mass produced Langster...that's just stupid...lol...
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Old 10-24-08, 04:57 AM
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Originally Posted by gestalt assault View Post
now $800 for a mass produced Langster...that's just stupid...lol...
what if you only paid $130 for your mass produced langster?
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Old 10-25-08, 03:35 PM
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Originally Posted by .jrmyrmx View Post
whatever man, at least im not spending $1500 on a single speed bike like many others on here.

ill probably go with a 12t cog to make it easy.
i know dudes with $1000 BMX'ers. my track bike cost about half that.
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Old 10-25-08, 04:27 PM
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Holy mother of god. BMX cog = SS freewheel kthnnx bye fixie fixie fixie fixie fixie fixie fixie fixie fixie fixie fixie fixie fixie fixie fixie fixie fixie fixie fixie fixie fixie fixie fixie fixie fixie fixiev
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Old 10-26-08, 09:14 AM
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Old 10-26-08, 11:08 AM
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Originally Posted by K_phomma View Post
Holy mother of god. BMX cog = SS freewheel kthnnx bye
Wrong.

SS splined cassette cog
thread on freewheel
BMX one piece drive cog (what the OP wanted to 'weld' to a hub)

Three different things.
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Old 10-26-08, 01:56 PM
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Originally Posted by .jrmyrmx View Post
i come from a bmx scene and i like like look of a really small chainring/cog. could i weld an 8 tooth driver on my fixie hub and use a really small chainring (keeping the same ratio). would there be any problems with doing this?

thanks,
jeremy
if your cog and hub are both the same material (aluminum or steel) you could probably weld them together somehow.

however, using an 8t cog is a pretty bad idea. a low number of engaged teeth / severe curve of the chain will reduce drivetrain efficiency, and the cog will also wear much faster with the stress concentrated on such a small cog. then once you've quickly worn out your welded-on cog, you'll have a bit of trouble replacing it.
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