Wheel width is the distance between the tire seat areas that span the rim (not the distance from the outer edge of the wheel to the relative edge). The wheel width partially increases in response to the increased tire width. However, the most important consideration for wheel width is that it is the proper size of the tyre to be mounted. Each tire manufacturer assigns a series of rim widths for each tire size; Even within this range, the mounting width of the tire will vary.

After installation, the actual width of the tire increases by nearly an inch in some cases when the narrowest to widest rims allow it. That may not sound like much, but it can be crucial when choosing tires and wheel kits. A tire mounted on a narrower rim within this range may fit the vehicle, but the same tire mounted on a wider rim may not fit.