A tire rim's width is measured starting from one tire bead seat area and ending at the opposite tire bead seat area. The diameter of the tire rim is measured using the same method.
The width of a tire is influenced by the width of the tire rim. There is a standard rim width recommended for every size tire and for the proper fit and most comfortable and safe ride, those recommendations should always be used.
It is important to understand the size, design and offset of the tire before changing options on any vehicle that are not factory. The wheel diameter is front to measured across the center, and the wheel width is measured across the barrel from the front to the rear.
The bolt pattern is determined by the arrangement of the lug holes, the number of lugs and the distance between the lugs and across the wheel's center.
The offset of the wheel is measured from the centerline of the rim to the hub mounting surface. A positive offset brings the tire and the wheel closer to the frame with movement, while a negative offset moves the tire and wheel farther away from the frame with movement.
Tires are clearly marked with codes that display their measurements, aspect ratio and durability.