Terminology

Pilot: Nominal diameter of center hole that fits over the hub or axle.

Rim Diameter: Nominal Diameter measured from bead seat.

Non-Reversible: Wheel will mount on one side of disk face only.

Chamfer: Breaks the sharp edges of mounting holes to assist in assembly.

Rim Width: Nominal width measured between rim flanges.

Bead Seat: Position where tire rests on rim and seals.

Centerline: 1/2 of rim width.

Click here for visual description of terms.

Bolt Circle (Pattern): The diameter of an imaginary circle drawn through the center of each lug hole or stud. Illustration on right.

Also called rear spacing. Distance from extreme back edge of the rim, not bead seat, to the mounting pad.  See Illustration. Lay a straight edge across the back of the rim and measure down to the mounting pad.  Nearly all custom wheels use this measurement method to indicate the location of the mounting pad in relation to the rim.