Its pretty much accepted by cyclists that cars will pass you with the same clearance you give the curb. Hug the curb, and cars will shave past you. Ride more assetively, about 2-3ft wide, and cars will give you a wider berth. The faster you go, the wider you ride. If there is not sufficient room to overtake you, you can take the whole lane by riding in the middle. You have to control the traffic around you.
Curbs are dangerous places, they are full of broken glass and drainage features. Cars turning into your road are looking for vehicles in the middle of the lane, not the edge. Pedestrians stepping off the curb are not looking at you. When you pass parked cars, you have to swerve out into the traffic, and risk getting hit by opening car doors.

All of this apparently arcane knowledge is distilled into the Effective Cycling course and book by John Forrester. To us experienced cyclists, EC is just plain common sense, but for newbies, there is nothing common about it. Read the book, do the course.