Folding Bikes - Not quite: Cheap BMX flip flop to fixed gear conversion

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geo8rge
05-19-07, 05:39 PM
If you remember I claimed you could convert a BMX flip flop to a fixed gear with the Surly Dingle sprocket. I retract that and apologize if I misled anyone.

I finally built my wheel. While the Surly Dingle does thread on the Freewheel threads there are some problems:

It still needs a lockring because if you pedal backwards it unscrews (why didn't I see that?). This was not a problem for me as the Harris flip flop hub is threaded for both freewheels and fixed gear lockrings.

I do not think there are lock rings threaded like freewheels. You might be able to "jerry rig" something. I do not think that on a freewheel only threaded hub, there will be any threads extending beyond the spocket to thread a lockring on anyway. Maybe you can solve some of these problems, but I doubt there is an off the shelf solution.

Possible thoughts: Thread it on with the strongest loctite glue, but I have trouble believing it will hold, who knows. It might be possible to drill where the hub and sprocket treads meet and put in set screws, could work. I think the Surly sprocket is steel so welding would be complicated.

Parts I used:

Harris flip flop hub
http://sheldonbrown.com/harris/fixed-hubs.html

Surly "Dingle" Two-speed Fixed-Gear Sprockets...Click Here!
http://sheldonbrown.com/harris/fixed-sprockets.html#dingle

Rincewind8
05-19-07, 07:27 PM
I do not think there are lock rings threaded like freewheels.
A lock ring for a fixed gear hub requires threading that goes the opposite direction than the thread for the cog. However, a bottom bracket lock ring has the same threading as track cogs. So it can be used to make a "suicide" setup a little more secure. I still wouldn't apply back pressure with this setup or even use it as a brake.
juan162
05-19-07, 09:57 PM
geo8rge,
People do use bmx flip flops for conversions, but they are called "suicide" fixed gear conversions because if it gets undone, well, you know the rest! They use loctite, just like you said,
Juan

jur
05-20-07, 02:49 AM
Sheldon recommends the use of an old-fashioned BB lock ring which apparently has the same thread, to lock the cog in such a case.