Originally Posted by Carcosa

I'm guessing your riding fixed right? Seems like it, just want to make sure.

I ran 46x16 for a long time in a flat city. Now that I live in a pretty hilly city, I switched to 46-15 and love it.

The one tooth change shouldn't seem like a big jumb but it's a 5 gear inch change. Definitely not nothing. It was enough for me to be able to get the downhill speed I wanted, even though I'm still spinning a pretty fast cadence. There are two 10 percent plus grades in town I've found that were the only things I had to walk up. But they start after 90 degree turns so you can't carry any speed into them. Luckily they aren't on any normal route.

For what it's worth my city is hillier than most of Brooklyn I've seen. Imagine Prospect Park all over.

Also, the LBS guy might not be leading you too far astray. A 15 isn't going to break, but I've read that you don't want to go much smaller than a 15 in the rear on a freewheel since the smaller cog can easier lead to throwing your chain. If you are riding fixed it shouldn't be an issue since you will more than likely be running a little less chain slack than a freewheel and the tension of constantly pedaling keeps the chain in place.

Finally, changing your chainring doesn't have any greater effect on spinning that changing your cog would do.