I used to run 48/16. This was great on the flats, hill sucked tho. I went to 48/18 and it's like a diff bike. Sometimes I wish I still had the 16t cog on, but when I come to a hill Im glad I have the 18t. I am pretty new to biking (started 2.5 months ago) and I can already tell my legs arent the same. You live in north bay? Depending where your at you def might want to go for mid to high 60's. You live in North Bay? Depending where your at it can get pretty hilly. Cog's are pretty cheap, if what you have dose not feel good try a dif one. To calculate how far one spin will take you divide the chain ring by the cog and multiply it by the diameter (in inches) of your wheel.

16/48 = 3. 3 x 27 (700c) = 81 gear inches.

I could be wrong but I think this is accurate.