Help Needed... Cranks slipping

Hi all,

Not having a good two weeks in terms of cycling. In under 150 miles of cycling i've had 4 puntures (and need a new tyre) and have somehow snapped two chains....anyway

My fixed is now up and running, but after 10 miles or so of riding it seems to have a problem when brakeing.

When i 'leg' brake, the cranks slip back/forward about 2-3 inches and the wheel does not lock. I have checked the cog and lockring and they seem to be tightened as much as they can be. The BB has no movement side to side and the cranks are in good nick.

Ive recently put on a 39T chainring and had a new chain fitted (its a 15T euroasia cog btw).

Any ideas?

although the cog feels tight, it will probably be that it is not tight enough. If it was the cranks slipping then they will be ruined, it could possibly be the chainring if you have it the wrong way round and the chainring bolts are not falling flush into the recessed bit, that can cause movement when decelerating and accelerating. but i would guess its the cog, needs to be nipped up.

right, ill have another look at the cog this evening then

Yep sounds like it's the cog/lockring, put the cog on, find a hill to go up, get to the top and put the lockring on nice and tight, should do the job.

Have removed cog/locking

Tightened cog with chain whip and then lockring has been tightened properly with a lockring tool. Is skidding fine now...will test it on a 50mile ride tomorrow

Just out of interest, was it a new cog? When i've changed mine it's needed tightening a few seperate times before it's settled.

woohoo, forum success.

Its a pretty new cog (under 100 miles done iirc)

I would also check chain tension is sufficient, and the chain for roller wear depending on how old it is.

Bike is fine, rode beautifully over the commute today.

Regarding punctures, i checked the tyre inside and out thoroughly after each punture. I think its just bad luck to be honest. 2 on the fixed, a slashed tyre on the road bike and another punture on the mtb