Rim/Wheel Glossary

APPROVED RIM WIDTH - Rim width sizes approved by The Tire & Rim Association for use with the tire.

BALANCED WHEEL - A wheel that is within 30 inch-ounces of balance.

BEAD SEAT - Surface of a rim that contacts the tire bead. The bead seat angle is usually 5° for tube-type tires and 15° for tubeless tires.

BOLT CIRCLE - The diameter of the circle which traces through the center line of the bolt holes. It defines the bolt hole spacing around the disc in a wheel.

BOLT HOLES - The holes in the disc of a wheel through which the bolts or the studs pass. For stud mount wheels, the bolt holes are chamfered and used to center the wheels.

BORE - The center hole (pilot) of the wheel. With hub mount wheels, it is used to center the wheel.

BUTT WELD - Transverse weld in a rim.

CAPACITY - Demountable rim or disc wheel maximum carrying load. Expressed in load (lbs.) and inflation pressure (psi) cold.

DESIGN RIM WIDTH - Nominal rim width. Rim width on which a tire performs best. It is approximately 75% as wide as the tire width designation.

DEMOUNTABLE RIM - A rim with valve locaters which is used with a cast spoke wheel to provide the method of attaching tires to the vehicle.

DISC WHEEL - A permanent assembly of a disc and a rim.

DOUBLE CAP NUT - The inner and outer nuts used to secure stud-mount wheels to a vehicle. The inner dual wheel is attached by an inner cap nut with a spherical radius and the outer dual wheel is attached by an outer cap nut with a spherical radius.

DUAL SPACING - Lateral distance from wheel centerline to wheel centerline in a dual wheel arrangement. It is determined by adding two offsets (disc wheels) or two offsets plus one spacer band width (demountable rims).

HALF DUAL SPACING - See “Wheel Offset.”

HAND HOLE - Opening in the disc area of a wheel for the purpose of valve stem access to inside dual tire and chain application.

HUB MOUNT WHEEL - Wheels that are designed to center on the hub at the bore of the wheel. These wheels generally have straight through bolt holes, since the bolt holes only supply clearance for the stud. Hub mount wheels are used with two piece flange nuts.

INSET - The lateral distance from the rim centerline to the mounting surface of the disc. Inset places the rim center inboard of the mounting surface.

LOCK RING - Third piece of a three-piece rim assembly which locks the side ring to the rim base.

LONG SIDE - The side of the rim which has a ledge.

MINIMUM DUAL SPACING - The minimum allowable distance between the wheel centerlines in a dual arrangement.

MULTI-PIECE RIM - A rim consisting of more than one part. Usually two pieces (rim base and side ring), or three pieces (rim base, side ring, and lock ring).

OFFSET - See “Rim Offset” or “Wheel Offset.”

OUTSET - The lateral distance from the rim centerline to the mounting surface of the disc. Outset places the rim center outboard of the hub surface.

RIM (also see "Demountable Rim") - The item that supports the tire. It may consist of one piece (tubeless drop center type) or two or three piece (tube-type).

RIM BASE - The major piece of a multi-piece rim assembly. It supports the tire bead on one side, and provides a locking mechanism for the side ring or lock ring and a bevel surface for attaching to a spoke wheel.

RIM OFFSET - The lateral distance from the rim surface that contacts the spacer band to the rim centerline.

SHORT SIDE - The side of the rim which does not have a ledge.

SIDE RING - A removable piece of a multi-piece rim assembly which provides lateral support for one tire bead.

SPACER BAND - Band of steel which separates two demountable rims on spoke wheels (also called “spacers”).

SPOKE WHEEL - A casting with three, five, or six spokes that attaches to the axle and provides a means of attaching a demountable rim to a vehicle. Also called “Cast Spoke Wheel.”

STUD MOUNT WHEELS - Wheels that are designed to center on the studs of a hub. These wheels have chamfers at the bolt holes into which a ball seat or conical nut is installed to center the wheel. The center bore of the wheel is only for clearance of the axle end.

TWO-PIECE FLANGE NUT - A nut attached to a washer that is used to secure hub-mount wheels to a vehicle.

VALVE HOLE - The hole in the rim into which a valve is installed to inflate or deflate the tire/rim assembly.

VALVE LOCATERS - The guides located on either side of the demountable rim valve slot or valve hole to properly locate the tire valve between spokes. Sometimes called “drivers,” “rim drivers,” “locating lugs,” etc.; they are either indented or welded on.

VALVE SLOT - Opening in a tube-type rim to receive the tire tube valve stem.

WHEEL - See “Spoke Wheel” or “Disc Wheel.”

WHEEL OFFSET - The lateral distance from the disc mating surface (surface between the wheels as a dual assembly) to the rim centerline.