lock ring jumping threads?
 

i just put together my fixy commuter with an IRO flip flop hub, soma cog and lockring (all purchased from IRO). I was going down a pedestrian overpass, and my lockring felt like it jumped a thread, because the cog unscrewed itself about a quarter turn. The cog pulled itself tight again when I hit flat ground, but i checked the lockring and it was a quarter turn or so loose. Does anyone know why this happens? Am I just applying too much pressure, or is the hub or lockring defective? I got all the parts brand new and rode it for the first time today. Any help would be greatly appreciated!

my guess is that you didn't have the cog cinched down as tight as it could go. when you rode up the overpass the cog got tightened down all the way, leaving a gap between it and the lockring, and when you put backpressure on the pedals to slow down, the cog unthreaded until it hit the lockring.

go ride up a hill, and then tighten the lockring down at the top.

do you have a whip? or did you just thread the cog on by hand?

This method, the 'rotofixa' method, is really quite effective at tightening cogs. I don't own a chain whip, so I either use the 'old chain in a vice grip' method, or the rotofixa method. I don't buy their, "don't need a lockring!" argument, but the ability to tighten and loosen cogs very effectively without a tool is a handy one to have.

http://204.73.203.34/fisso/eng/schpignone.htm

Tighten your cog this way, and then tighten the lockring down on it with a lockring wrench. That should do it for you.

peace,
sam