I have a Sugino RD crankset and need to pick up a new cog. The crankset is 165mm and 48t but I'm not sure if they are 1/8" or 3/32" - any ideas? the stock cog is 3/32" but I suspect the cog could be incorrect not because the stock listing says the bike comes with 19t and a Surly cog - but it's actually 17t and no name/generic.
The Sugino RD chainring is 1/8 inch, so if you're getting a new cog, get a 1/8". Make sure you get a 1/8" chain too. The number of teeth is up to you. I have the same crankset and run a Euro Asia 17t cog and I find the ratio to be ideal. I had 16t rear for a few years, and recently changed. Adding one tooth in the rear has made my knees much happier.
Gios Compact Pro , Gios fixed gear, Pedal Force RS2, CAAD5 single speed.
I run an 8 speed 3/32 chain on my sugino rd, a 48, with an 18 fixed cog, and a 19 ss freewheel. It is windy today and I flipped the rear wheel over and rode the 19 freewheel for the first time - I always rode fixed - and it was real fun. Makes the intersections a little less interesting when you can coast.