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 centerline 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-piloted 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 (Ibs) and inflation pressure (psi) cold.
DESIGN RIM WIDTH – Nominal rim width. Rim width on
which a tire performs best. Approximately 75 percent as wide
as the tire width designation.
DEMOUNTABLE RIM – A rim with valve locators 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-piloted 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 bandwidth (demountable rims).
HALF DUAL SPACING – See “Wheel Offset.”
HAND HOLE – Opening in the disc area of a wheel for the
purpose of the valve stem access to inside dual tire and chain
application.
HUB-PILOTED 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-piloted 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 line
inboard of the mounting surface.
LOCK RING – Third piece of a 3-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).
OUTSET – The lateral distance from the rim centerline to the
mounting surface of the disc. Outset places the rim centerline
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 pieces (tube-type).
RIM BASE – The major piece of a multi-piece rim assembly.
It supports the tire bead on one side, provides a locking
mechanism for the side ring or lock ring, and provides 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 (Demountable
Rim see page 43).
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 that separates two
demountable rims on spoke wheels (also called “spacers”).
SPOKE WHEEL – A casting with 3, 5, or 6 spokes that attaches
to the axle and provides a means of attaching a demountable
rim to a vehicle. Also called “Cast Spoke Wheel.”
STUD-PILOTED 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.
SUPER SINGLE – Single wide base wheel.
TWO-PIECE FLANGE NUT – A nut attached to a washer that is
used to secure hub-piloted 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 stems.
VENT HOLE – Opening in the disc area of a wheel for the
purpose of air ventilation.
WHEEL OFFSET – The lateral distance from the disc mating
surface (surface between the wheels as a dual assembly) to the
rim centerline.
