How are rims measured?
 

Older civics have fourteen-inch rims. That is the rim itself, not the lip, right? So when we measure a car based on the wheels, we are off slightly, correct?

Well, I will keep measuring incorrectly, and remember that detail, but not try to compensate for it.

"Most cars come with horrible narrow little tyres and 13 inch rims. More recently the manufacturers have come to their senses and started putting decent combinations on factory cars so that's not so much of a problem any more."

The easy way to do this is to remember that 14" tires only fit on 14" rims - and 14" rims only take 14" tires. No other combination works. So if a tire is mounted on the wheel, look at the tire size.

The wheels are usually marked on the back side. It might be in code like 14X6J - which means 14" diameter, 6" width with a J type flange.

And lastly, every vehicle has a vehicle tire placard that tells what the original tire size was and the specified inflation pressure for that size. The vehicle tire placard is usually located on a doorframe or in the glove box, but sometimes it is in the trunk or on the fuel filler door.

My link shows a diagram of the lip and other goodness, I think its all you need to figure it out.

The only time this matters is on those blasted 16.5" rims

I always have to chuckle when I see DO NOT MOUNT ON 16.5 RIM on the side of a 16'' tire.

Well ... it's not good ,though, as a lot of people got hurt doing that.