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tl;dr: tighten the cog a lot then tighten the lockring.

If this is a standard thread on cog (I'm not sure what "like the cog is slipping over the grooves on the hub") means, make sure you tighten the cog down with a chain whip before you tighten the lock ring. If you have any play in the cog, tightening the lock ring won't matter: pedaling hard will rotate the cog forward and then extra play will let it rotate back when skidding. The play can also slowly work the lockring loose. If you asked the shop to install the cog it should already be tight but if you just had them tighten the lockring they might not have checked the cog.

I doubt that a good hub, cog & lockring will slip when properly set up. I mean Chris Hoy is a pretty powerful rider and seems to get by. You shouldn't need locktite, in fact I'd recommend greasing the threads so you can get the cog back off.

I've had bad experiences with some cheap hubs: I stripped both lockring threads of a fixed-fixed IRO MTB hub (it may also have had something to do with the extra traction of a MTB tire). So you might want to upgrade your hub, cog and/or lockring.

If you're really worried about the cog slipping you can always re-space a front ISO disc hub and use a bolt-on cog. That's what Chris & Stik do for fixed gear MTB'ing and it seems to work pretty well.

Tighten them both with a chain whip; go climb a hill forcing yourself to crank as hard as you can on the cog; then tighten the lock ring before you skid. The idea of a lock ring is to tighten as the cog loosens. If there is any play in that scenario, it was never where it should have been.

Good advice ^^^^

Tighten the cog by pedaling up a large hill. then without back pedaling tighten the lockring with the correct tool.

Forgive me if I'm being Mr. Obvious here, but have you checked that there is not too much slack in the chain? If you occasionally here something like a ratcheting noise, it's possible that's the chain skipping on the cog, especially if it's a tiny cog. The chain should only move up and down about 1/2" at a point half way between the gears, but it also should not be guitar-string tight, either.

Also a cheap hub/locking/cog combo can be too narrow

and never actually be tight enough. Like the threads

are a bit too wide, the cog is a bit too narrow and

when you tighten down the lockring, you are actually

just tightening it down onto the threads, not the

cog. I would just buy all dura ace

What Steevo said too.

Tighten the cog, then the lockring. Cog, then lockring. Cog, then lockring.

You may want to try what is known as the "rotafix" method of using your frame and wheels as the chainwhip. It allows you to get the cog on way tighter than a chainwhip or riding up a hill (leverage my friend).

A properly installed fixed cog/lockring should work fine. Something isn't right if it is coming undone, it's not because of your incredible strength or anything.

does it happen only after you "do some hard pedal-braking?"

Thanks everyone for all the responses!

That was my first impulse too the first time this happened. So I took it apart, and discover that the cog itself is not a threaded part. Instead, it's got a scalloped inner diameter that mates with a similar shape on the hub. I'd never seen anything like this before, so I assumed is was some sort of standard fixie setup. I'm guessing that's not the case now.

I have a couple of photos, but don't know how to post them here...

So, when I crank down on the locking ring, there's nothing to lock it against, except for the cog itself, so I'm just cranking it against the hub. Seems like a faulty system to me.

you mean it's splined like regular cassette cogs?

Yes - splined is the word I was looking for. Couldn't figure out how to post photos here, so I put them on the brewery site...

http://eastendbrewing.com/node/881

Ah, one of those. Seen them, can't say I'm familiar. Some of the splined systems have a tendency to develop some play in them.

"does it happen only after you "do some hard pedal-braking?" "

Yes, that's what seems to loosen the lock ring. But for it to skip across the splines, it would have to be WAY looser than it is now. I would instead expect it to just feel sloppy.

Oh, and chain tension is very good, w/ less than 1/2" of deflection. Shop set it a little tighter than I did, but like I say, it still happened.

Yeah, a little play is what I might expect from a setup like this. It's when it gives way and I get a 1/2 a crank's revolution with suddenly no resistance... THAT'S what's going to throw me off the bike or onto the top tube. Or maybe just keep me from stopping.

yeah that setup looks ripe for wearing down and developing slippage/play. especially as rounded as the splines are. bizarre.

I think I just discovered something. The color difference shows up more in the photos than in real life: The part that's mates with the cog is not a part of the hub. It's a threaded on piece that can be tightened or loosened. (Maybe it's on there for quick cog size changes?)

Looks like I've been chasing the wrong union...

So I'm betting that the original "crank it down without braking, then tighten the lock ring" advice will still work here. Off to give it a try, and hopefully not land on the top tube!

I'll let you know how it works. Thanks everyone!

if it's a regular threaded hub you may want to just get a new cog altogether. that design just seems too flimsy to me for the heavy forces a fixed cog experiences

It does seem odd to cut the mating surface like that. Why not something more like right angles?

It's all brand new gear, so I think it needs to work, or I get some help from the manufacturer on it. Worst case, I flip the wheel.

With the continuous wave pattern, forces are distributed over a larger surface area. If you had something with right angles, all the force is concentrated on those points where your right angles meet.

You're onto it Scott.

You need to put the cog on the splined interface, tighten the carrier thing onto the hub as much as possible, and then tighten the lockring down on it. It looks like the lockring tightens against the face of the carrier to hold it in place and to hold the cog on the carrier as well.

Something to consider is what Steevo said though, it is possible that the splined carrier bit isn't as thick as it needs to be on your particular hub and thus you are tightening the lockring just against the hub body, doing not much at all. There are paper thin spacers out there that you could potentially place behind the splined carrier.

**I'm not sure about it, but it looks like the carrier and/or lockring might use the same tool that is used for Shimano style external bottom brackets. Not sure just from the images though, and I've not worked on one of those setups to know if it is a Sugino specific tool or not.

It looks like the lockring threads are right-handed. That means that the tremendous force created by back pedaling will force the cog to rub against the lockring in the same direction as you would turn it to unscrew it. In a typical track hub, the lockring threads are left handed. My fixed gear has an old hub from 1975 with no lockring and the cog was put on with a whip, but I am very aware of that whenever I need to stop quickly. I can only trust it to a point. It will come loose.

Thanks Brad. Appreciate the encouragement... and redirection to Steevo's word. I hauled it up a couple of steep hills tonight to try and set it tightly. Ready for the lockring now.

Steevo: Yes, that occurred to me too, as I have an angle grinder with the same design flaw, where the cutting wheel spins freely. There is a TINY bit of rotational slop in the cog before it's tightened down, but once tightened, it goes away. Based on this I dismissed the notion. But with all this on-and-off, I'd expect some wear on the face of the lock ring. And it still has it's factory finish black, un-scarred. So I'm suspicious. I'll dig up a spacer tomorrow at the brewery in the boneyard and give it a go.

Morningsider: It may be hard to see on that photo (especially with all the limestone powder from the trail), but the lock ring threads are indeed "backwards" or LHT on the hub. Or at least they are on this side of the hub. Too bad, it would have explained it nicely!

Thanks everyone. This has been VERY helpful.

I ran a Miche setup that was very similar to yours (splined cogs), and never had any issues with the cog/carrier interface wearing out. I reckon I put 15,000 miles on that hub. Cogs certainly got replaced over time, but the interface never wore to point of slippage.

This is probably a completely dumb question, but does it matter which way the lockring goes on? Is the "up" side in the picture the cog side?

No offense to your purchase, but what was wrong with

a traditional track cog setup that somebody was like

"yo lets do this new thing" ... and created a new

standard.

- says the dude with 2 sets of isis cranks.

I like that the lockring looks like it uses a outboard bearing bottom bracket tool. That is a smart design.

@ Scott:

To post a photo: the photo has to be on the internet somewhere already. so if it's a photo that you want to post, you need to put it on flickr, photobucket, your site or something first.

then, you get the photo's url-it usually ends in .jpg

on many computers, you can right click on the photo, and select "copy image location"

then type the html:

img src="http//www.yourphotourlhere.jpg"

except add the "<" ">" around it.

I had this set-up and I liked it a lot. It is nice because you only need one tool for cog removal/installation--an external bottom bracket cup tool. The only down side is you can't use a socket like the Park BBT-19 (iirc) to remove the carrier.

I never had any problems with the splines wearing. I think the cogs teeth would wear out way before splines would.