To ensure correct fit between a tire and rim, all manufacturers of wheels and tires comply with standard dimensions, as recommended by tire and rim associations.
The width of the rim is the distance across the rim flanges, at the bead seat. Its diameter is the distance across the center of the rim from bead seat to bead seat.
The shape of well-based rims is provided by a letter code, such as J, K, JJ, and KK.
The width of the rim and the diameter is traditionally stated in inches.
A rim designated 7 JJ by 14 would refer to a rim measuring 7 inches across the rim flanges, and 14 inches in diameter from bead seat to bead seat, with the profile conforming to a JJ code.
The rim width and diameter can also be stated in millimeters. Metric rims are not interchangeable with Imperial rims.
The tire must be an exact fit on the rim, to fulfill a number of functions.
