EAI cog, Pista, & stripped hub
 

Hey fellow fixed gear riders--

Long story short, 3 months ago I swapped a SOMA cog for an EAI onto my Pista Via Condotti. A few nights ago while skidding my cog slipped about a quarter turn backwards into my lockring. I walked the bike home and when I popped the wheel off I noticed shards of metal sticking out from under the lock ring. Like it had been through a steel lathe. No bueno.

The threads on inner stepped hub (for the lock ring) are gone. As in, seriously stripped. The lockring will just spin endlessly against the cog.

I did some googling and Phil Wood recommends against using EAI cogs for this reason; apparently there are ~1.25 more turns in an EAI cog than others, meaning that the fatter cog can't get properly seated in the thread. With enough force I suppose it backs itself out, punches into the lockring, and because the lockring spins the opposite direction, it just pushes the lock ring out and takes the threads with it.

So the hub is done for. It definitely needs to be replaced. I'm wondering if anyone has any experience with EAI cogs on Pistas doing this (I didn't see anything), and further if Bianchi is at all helpful (bike's still under warranty, I believe) or if I'm SOL.
All the parts were correctly installed and torqued. I haven't found any warnings from Bianchi about this issue.

Thanks.

Was the EAI cog the cog that came on the bike from the factory? I highly doubt Bianchi will warrantee anything since you have "modified" your bike from the factory condition. If anything, i'd hit up EAI to see what they say.

Sucks man!

If that's true, you wouldn't be here posting a thread about having a stripped hub.

There's absolutely nothing wrong with the hub, cog or bike. If you're going to ride a fixed gear bike, you should learn how to properly install a cog and lockring.

It may have been correctly torqued the day you installed it but things do loosen. You're supposed to keep an eye on it over time as you ride.

Also, it's especially important that you retighten the lockring after the 1st ride with a new cog. Reason being, the torque from you pedaling is by no means replicable by a chainwhip and the final settling/ tightening of the cog under your pedaling will cause your lockring to no longer hug the cog and subject to loosening with road vibrations.

"With enough force I suppose it backs itself out, punches into the lockring, and because the lockring spins the opposite direction, it just pushes the lock ring out and takes the threads with it."

Say that again?

First, that would require a ton of torque. I'm sure someone could do the math but 2000 ft lbs might do it. But frankly, I'm not sure you predict the correct result from that much force. I think the locking would not move - that the cog would strip its hub-threads. Or maybe the hub would blow out the spoke holes. Or maybe the pedal spindle would go first? Perhaps the chain stays would crumple. Or the chain would break.

Thread hijack - what's the weak point in this mechanical transaction. Assuming someone's going forward on a bicycle and can exert enough reverse force on the pedals to make something break. What breaks? Let's assume that the bicycle can't skid and can't go backwards.

the chain

Two things were done wrong here. The drivetrain wasn't installed properly, and you were skidding. Learn how to properly service your bike and get at least a front brake.