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Old 09-26-05, 11:08 PM   #1
LubbockIsFlat
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BMX Conversions

I recently acquired an old BMX bike from a friend, and I really wanted to try and adapt the gear system of an old mountain bike(the hub, derailers, and chainwheel) to fit it. Unfortuantely, I am new at bike tinkering, so I am asking you guys for some direction. By new, I mean have never done it before.
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Old 09-26-05, 11:22 PM   #2
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You need to adapt/make some kind of derailleur hanger, and you'll need some cable stops. Also, the hub spacing will not be the same.
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Old 09-27-05, 08:22 AM   #3
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You'll need to fit some sort of guide above the chainwheel to stop the chain coming off all the time. It's probably easier (if you can find one) to get a hub gear like a Shimano Nexus, Sturmey Archer or Sram Spectro. Then spread the seatstays wide enough to slot it in and badda-bing you're speeding along with up to 8 gears...

(A bit like my Raleigh Twenty (link below) Not a bmx but principle and wheel size is same...)
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Old 09-27-05, 12:27 PM   #4
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Thanks for the help guys, but I still have a few questions:
Could I perhaps sacrifice changing gears at my chain wheel and just static mount the front derailer to hold the chain on?
Also, would it be easier or cheaper to try and put an internal gear system in?
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Old 09-27-05, 02:25 PM   #5
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Easier to use an internal hub, perhaps cheaper in the long run. A Nexus 7 can be had on ebay for about $125, if you're lucky. Parts and labor on a derailleur system would probably be more. A fixed front derailleur would just be friction, for what you suggest. The problem is the chainline going from a single chainring across several cogs on a frame with short chainstays. Maybe a narrow 5 speed?
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Old 09-29-05, 03:13 PM   #6
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Stingray guys do it all the time. If the frame is mild steel it's very easy to spread the rear triangle to accept a wide hub. Most serious bmx bikes are
4130 at the least, and it gets difficult to bend these frames. I have a few old BMX frames, and I have thought of having an old Shimano 333/3CC laced into the back rim. No frame stretching, and multiple speeds. IE the best of both worlds. What you do with all that speed on a bmx bike is a matter of concern though, lol. It would make one hell of a board and brick ramp jumper, lol. Here's a Stingray I converted to five speed. Eventually I plan to make the front sprocket shift as well. A Nexus 7 speed bmx?? Wicked idea!!!

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Old 09-29-05, 03:19 PM   #7
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I am running the larger chainring, a 50 cog. No problems with the chain staying on?
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Old 10-25-05, 10:00 AM   #8
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I need to tell someone who will see this so i posted it here...I have a new trick, its a combo trick you start out doing a tailwhip then when the bike gets to your right side spin your body with your left foot on the front peg to the left so that the front tire is straight with the back of the bike and put your right hand on the seat with your left still on the handel bar grip and push the front tire with your right foot to get going and ride it like this as long as you can... i have never been able to get back to the seat from this trick i just get off and turn the bars back around and get back on.

have fun trying this trick
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Old 10-25-05, 10:30 AM   #9
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Kind of a crappy pic, but here you can see the grip shifter on the BMX cruiser I built for my girl.



I used a Sram T3 hub, with no internal brake. The spacing was perfect.
The only tricky part was machining a cable stop that bolted to the chainstay brace.

The speeds are normal 44/16 ratio for 2nd gear, and + or - 30% of that for 1st and 3rd.
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Old 10-25-05, 11:01 AM   #10
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New@It,just get started!If you have the old M/B start taking off what you want and bolt it up to the BMX.Worst that can happen is it doesn't work right--not the first time that's happened to me.But just by trying you'll gain the knowlage to get it right(next time).Take a look at the Stingray photos as well.
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Old 01-02-08, 11:10 AM   #11
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I put a 5 speed deraileur system onto a Raleigh Wild Cat BMX.

I got a single speed shopper bike rear wheel...was a skinny 20 X 1 3/8" wheel.
I took the axle out. It had spacers on both sides. I swapped them around.
I managed to get the 5 speed freewheel on there.
The only frame mod I did was to file down the the bottom of the drop out.
The frame DID NOT need widened. But only cause of the wheel I was using.
That was so the rear deraileur, could mount correctly.
It had a claw that mounts under the rear wheel nut, I took it off the mech.
Then I turned it round, as the drop outs faced backwards
Ran a full length outer casing. Would recomend proper SIS gear outer casing.
Its much less flexable, better gear shifting
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