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Singlespeed & Fixed Gear "I still feel that variable gears are only for people over forty-five. Isn't it better to triumph by the strength of your muscles than by the artifice of a derailer? We are getting soft...As for me, give me a fixed gear!"-- Henri Desgrange (31 January 1865 - 16 August 1940)

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Old 09-01-08, 10:25 AM   #1
TreeUnit
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BB Lockring as Fixed Gear Lockring

Several weeks ago, a visitor to the local bike co-op described to me a sort of suicide hub he was riding on. The hub consisted of a standard screw-on freewheel hub with a track cog screwed onto it, and a bottom bracket lockring screwed on the outside of the cog to hold it in place.

I decided to give it a try. After two weeks, I am happy to report that this variety of suicide hub has worked well for me. The cog is still securely in place, and I have not experienced any "slipping cog".

So what does the FG community think? If this setup proves to be effective on a widespread scale, any screw-on freewheel hub could become a fixed-gear hub, no need for a track hub or rear wheel.
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Old 09-01-08, 10:33 AM   #2
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Where you went wrong was getting ideas at a bike co-op.
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Old 09-01-08, 10:34 AM   #3
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I think there was a mis-communication somewhere in the description here. A track lockring has a significantly smaller diameter than a BB lockring, and so it is impossible to screw them both on the same threads. Plus, the track lockring threads are reverse.

I am pretty sure that what it was was a normal road hub (that had been redished and respaced probably) with a cog screwed on and then a BB ring screwed on after it. The BB ring will not be an actual lockring in this application since it threads in the same direction (and do not "lock together"). THe BB ring really only adds a few more threads of friction to resist it and the cog coming loose. It probably does add a bit, but not much.

Nothing necessarily wrong with this set-up, but it is probably not a good idea to try to skid stop with this set up.

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Old 09-01-08, 10:39 AM   #4
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i have a mavic wheel on an old maillard hub. both sides are fixed/fixed. and they both use bottom bracket lockrings. ive tried to screw on a track lockring, but the lockring was too small.
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Old 09-01-08, 10:58 AM   #5
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Originally Posted by jgedwa View Post

I am pretty sure that what it was was a normal road hub (that had been redished and respaced probably) with a cog screwed on and then a BB ring screwed on after it. The BB ring will not be an actual lockring in this application since it threads in the same direction (and do not "lock together"). THe BB ring really only adds a few more threads of friction to resist it and the cog coming loose. It probably does add a bit, but not much.

Nothing necessarily wrong with this set-up, but it is probably not a good idea to try to skid stop with this set up.

jim
That's exactly what I described. I have encountered no difficulties with skidding and stopping so far.
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Old 09-01-08, 11:24 AM   #6
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Whoops. So, you did. Somehow I read an extra "track lockring" into your original question. Sorry.

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Old 09-01-08, 11:27 AM   #7
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i have a mavic wheel on an old maillard hub. both sides are fixed/fixed. and they both use bottom bracket lockrings. ive tried to screw on a track lockring, but the lockring was too small.
At the risk of looking like a fool twice in the same thread: is this possible?

Is the cog not the normal size? Seems like the cog would have to have larger thread diameter to fit over the lockring threads.

Did the BB lockrings thread on the normal way, or reversed? If they go on the normal way (and the cog HAS to go on the normal way), then it is not really functioning as a lockring.

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Old 09-01-08, 11:33 AM   #8
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i have a mavic wheel on an old maillard hub. both sides are fixed/fixed. and they both use bottom bracket lockrings. ive tried to screw on a track lockring, but the lockring was too small.
that means the hub is free/free
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Old 09-01-08, 11:46 AM   #9
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"THe BB ring really only adds a few more threads of friction to resist it and the cog coming loose. It probably does add a bit, but not much."

It's a little different, right? It's like how a hub works- the nut that goes outside the cone nut doesn't just add more threads, it sort of fuses together with the cone nut. In terms of the physics I suppose it's the difference between static and kinetic friction. The static friction is higher and having the extra lock ring (though threaded in the same direction) adds an area of static friction, so that if the inner cog unscrews it becomes more difficult to continue unthreading once it hits the lock ring.
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Old 09-01-08, 11:55 AM   #10
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As near as I can tell, the cog and lockrign are held solidly in place because they push off of each other. This outward pushing in turn pushes their threads against the threads of the hub very, very hard. The cog thread/hub thread friction is so great, it can hold up even against skids.
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Old 09-01-08, 01:07 PM   #11
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Quote:
Originally Posted by samwell View Post
"THe BB ring really only adds a few more threads of friction to resist it and the cog coming loose. It probably does add a bit, but not much."

It's a little different, right? It's like how a hub works- the nut that goes outside the cone nut doesn't just add more threads, it sort of fuses together with the cone nut. In terms of the physics I suppose it's the difference between static and kinetic friction. The static friction is higher and having the extra lock ring (though threaded in the same direction) adds an area of static friction, so that if the inner cog unscrews it becomes more difficult to continue unthreading once it hits the lock ring.
But, consider that one does not generally tighten the cog and BB ring AGAINST each other. The cog is tightened against the shoulder of the hub and the ring is tightened against that. As I understand it, this just extends the thread area.

Don't get me wrong, I am not saying it is not a useful cobble. Nor am I saying that a BB ring does nothing. But it does not "lock" anything in place. I run a couple of bikes this way myself.

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Old 09-01-08, 01:22 PM   #12
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THe BB ring really only adds a few more threads of friction to resist it and the cog coming loose. It probably does add a bit, but not much.
It's acting in a manner similar to a jam nut, quite common and functional if done properly.
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Old 09-01-08, 01:52 PM   #13
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It's acting in a manner similar to a jam nut, quite common and functional if done properly.

In order to actually jam them together, one would have to tighten down the cog, tighten down the ring, and then put counterclockwise force on the cog and clockwise force on the ring. You sure you want to put any loosening force on that cog?

In any case, I think the "jamming" you are talking about is really not all that relevant in this high-torque application. The forces involved in a headset, and even in loose-ball axles are not like what we have here. And notice how poorly those hold there.

I think that tightening down the cog as tightly against the hub shoulder is the best bet. then maybe throw on the BB ring for good measure if you feel like it.

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