Originally Posted by
noglider
Actually, the second measurement is not the width of the tire as measured directly. It is the effective width, which is calculated by spreading the tire out, measuring the distance between the beads, and dividing by 2.5. This is what I remember from reading the Sutherland's manual in 1983, so I could be remembering wrong.
OK, this may be the exact definition of tire width but to us ordinary users it is very closely approximated by measuring the outside width of the tire as mounted on a rim of standard width for the application.