I've been riding and daily commuting the same set of wheels for a while now with no issues till this past week.

While coming up to a light I will apply backward pressure on the pedals and feel a 'slip' in the drive-train of about 1/10th of a pedal roatation. This generally happens when I am nearly at a complete stop and have a good amount of my weight on the rear facing pedal. I ride with two brakes and use them so it is only within the last few feet of stopping that I am coming out of the seat....not skid stops for me.

When I start pedaling again I get same amount of slip, but this time when pressure is on the forward pedal. I do most of my starts and stop while standing on the pedals.

What I don't get is that I keep my cog/lockring tight. When I took everything apart it looked and felt like all the threads were in good working order. I've tested the threading any way I know and all seem to be in working order.

Could the cog width be too narrow or my lockring be a piece of poop? I ride more aggressively now than I ever did in the past (good things happen when you get back into shape) so I am not sure what I am doing to cause this.

UPDATE: 07/11/11 Problem solved.

I decided to tackle the issue again tonight after not getting any progress with the bike over the last couple of days. I did all sorts of tests to see why I couldn't get the cog to tighten down properly. I even did the riding up a hill and walking back down to tighten the cog and then going to town on the lockring. Nothing seemed to help. I went to far as to take video at the level of the cog and when there was slippage I couldn't see the cog move at all.

I was about to give up when I caught where the movement was coming from.....it was my f***ing chain ring bolts that were loose. It was just loose enough to slip an 1/8th of an inch in one direction or another from the center. I tightened those down and the problem was solved.

That's what it feels like when the lockring isn't tight enough. What are you using to tighten it down? I was never able to get my lockrings tight enough with a standard lockring spanner, so I ended up getting a hozan lockring tool. Never had a lockring slip since.

You can tighten your lockring until your arm breaks but if your cog isn't properly tightened first, you're wasting your time and the cog will just keep slipping back and forth - eventually ruining your hub.

I'm using this....

Is it a track hub with the 2 different sizes? the cog may be too narrow and need a spacer for the cog to be far enough out to lock against it properly.

Maybe BB is loose?

i have had this problem before even using the tighten, ride, and tighten approach. My solution: I rotafixed my cog before tightening down my lockring. I know the method is frowned upon but i really havent had an issue since

How would that make your drivetrain slip?

It wouldn't. Another classic example of evil not knowing what the hell he's talking about.

Luls!

Common sense is certainly lacking, in a fixed gear drivetrain there is only one place there could be slipping.

Yeah...the bottom bracket, right?

I wish Adriano were here to reply to that one

If the slipping is coming from the BB, there are larger problems at hand, like breaking the laws of physics.

I heard your drivetrain will inadvertently slip at the BB if you only post non-driveside pics of your bike.

i've had a similar problem. i went on a ride to the beach and heard squeeling noises coming from my bottom bracket. then the crank just slipped forward when i applied pressure hard from a stop. it slipped almost a half turn. i dont know what the problem is exactly, but my lockring and cog should be properly tightened. i havent done anything to the cog since i originally got it, but i do check my lockring to make sure its tight from time to time. everything seems to be properly tightened so what might the problem be?

i looked at the markings on the bottom bracket and they dont change position at all, so i'm left to think it must be something with the spindle? the cranks are not stripped btw, they are also in good shape. any ideas?

UPDATE: Problem solved.

I decided to tackle the issue again tonight after not getting any progress with the bike over the last couple of days. I did all sorts of tests to see why I couldn't get the cog to tighten down properly. I even did the riding up a hill and walking back down to tighten the cog and then going to town on the lockring. Nothing seemed to help. I went to far as to take video at the level of the cog and when there was slippage I couldn't see the cog move at all.

I was about to give up when I caught where the movement was coming from.....it was my f***ing chain ring bolts that were loose. It was just loose enough to slip an 1/8th of an inch in one direction or another from the center. I tightened those down and the problem was solved.

See post #3.

Come on, lets use our brains here. If your cranks were slipping that much, your crank arms would no longer be opposite from each each other, which would probably be noticeable, and the spindle would have have be rounded out on one of your cranks, which would be pretty easy to see visually if you took the bolt out. Another way your crank arms could be slipping would be if the spindle broke in half, but then there would be no resistance on the left crank arm, which would also be noticeable. Both of these scenarios are very unlikely (I'm sure its happened at least once though), and if that really was your problem, I think you would be able to recognize it. Take your bike to the shop and have them properly tighten your cog and lockring before your strip your hub. If you really think about it that is the ONLY place a fixed gear drivetrain could be slipping.