how would you compare the quality of EAI cogs to soma cogs?

go with eai.

I've heard great things about EAI cogs....but my EAI cog and Izumi chain are noisy. I still like it better than my Surly cog, however. I've never tried a Soma cog.

i have eai cogs, but soma says there's are cro-moly sumtin sumtin, so then they should be strong?

They're cogs. Neither is cheap (as in bad), and other than finishes, they look a lot alike. Pick whatever company you like more and be happy with your choice.

I just put a soma cog on my bike when i switched to a 1/8th drivetrain and its terrible. It has a weird tooth profile that catches the chain and causes all sorts of bad noises and rough spots in the crank rotation. I switched it out for an EAI and it's nice and smooth now. I'll never touch the somas again.

Just out of curiosity, was the chain and soma cog new. What you are describing sounds like a new chain on a worn cog.

I use & like Soma cogs, 1/8", but haven't used EAI. The Somas are quiet, long-wearing, and function at least as well as the Miches I had before...

soma vs. EAI right here: https://www.bikeforums.net/singlespeed-fixed-gear/117522-eai-round.html

There are at least some Soma and Surly cogs that are made with narrow gullets (the gap between the teeth). With certain chains, the chain roller is slightly wider than the gullet, so the chain actually jams into the gullet and has to be yanked out by your pedaling action. At best it sounds noisy, at worst it locks the chain up in the cog and you just start skidding or you pull the wheel in the stay ends. I don't see the problem all the time, but this last year we've had too-frequent problems at the track with these cogs. It got to where we had a couple Dura Ace or EAI cogs around just for those who showed up with bum cogs.

Another issue is the quality and type of threading on the cogs. The incidence of stripped hubs goes up with cogs other than EAI, Dura Ace, Suntour, Sugino, and Phil. There are two different cog threadings available -- ISO and British -- and they are almost but not quite compatible. You can force one onto a hub threaded with the other, but you're eroding the threads on the hub and shortening the life of the hub. Sooner or later, with enough changes and/or enough force applied, you'll simply strip the hub. So you want to keep an eye on the choice of cogs and hubs. Even if they're made of a decent grade of steel, you have other considerations in the cog you pick.

yeah, i had to force a EAI cog onto my miche hub, it works,but how long will it last before threads are shot.

The chain, chainring and cog were all brand new. It was a wipperman 152 chain, and vuelta chainring. My problem sounds exactly like what 11.4 described. Its possible that, with a different chain, the problem wouldn't have occurred.

EDIT: Actually, rereading 11.4's post, that wasn't quite the problem I had. The problem that i had was the tooth profile on the cog had a ridge that would catch on the ends of the narrow links of the chain when the tooth was in the wide link. this would lift the chain until the tension built up, the snap the chain back onto the cog. It was worse when I put backpressure on the chain. I blame gravity for that.

I had a similar problem with a NEW Izumi chain and a USED Surly cog (both 1/8")....I assumed that it was because the cog was worn. It turns out that that the Surly cog is worn, but I got it to work semi-smoothly with a new KMC chain. However, it is just utterly incompatable with the Izumi chain and it made horrible rough grinding noises very similar to what you are describing.