The weight of a truck and trailer combination and its entire contents.

Gross train weight. Same as GCW.

Total weight of fully equipped truck and payload.

The number of revolutions of a driving gear required to turn a driven gear through one full revolution. For a pair of gears the ratio is found by dividing the number of teeth on the driven gear by the number of teeth on the driving gear. Changing tire size will change the effective gear ratio. An increase in loaded radius will increase ratio, increase speed and reduce power.

A separable mechanical connector used to join air line hoses when combination vehicles are coupled together.

The complete rubber/fabric/steel just before being cured.

The channel between ribs in the tread of a tire.

The cutting of a tread design into tread rubber where a design does not already exist. Also altering an original design, i.e. cross-grooving to increase traction.

Splitting or cracking of the rubber (undertread) at the base of the grooves, between tread ribs. Primarily caused by growth in textile casings.

The stretching of textile tire cord materials due to heat and loss of strength, resulting in the casing increasing in size.

See rim terms.

Uneven wear of tread blocks on a tire. The trailing edge of the block often tends to wear at a faster rate that the leading edge.

Additional spring device permitting greater load on axle

The base having studs protruding from its face upon which the wheel is mounted to the vehicle.

A register showing miles traveled by vehicle mounted directly on the axle hub. It is popular to record mileage for leasing of vehicles or tires particularly on trailers, since there is no other odometer present.

To inflate with water in place of air. (Also see liquid ballast).

Loss of road contact due to the buildup of water between tire tread and road surface. It occurs when factors, including speed, water depth, tread depth and inflation pressure, so combine that lifting force is exerted under the tire.

The energy lost and not returned, when tire materials are subjected to stress in any direction. Lost energy is converted to heat through molecular interaction, and since rubber has poor thermal conductivity, internal temperatures of a tire can build up rapidly under repeated flexing.

Rupture to a tire resulting from shock of striking a chuck-hole, rock curb, etc. and not caused by cutting.

The sum of the camber and kingpin inclination angles. This angle is designed into the steering knuckle and must remain constant

One wheel position can move vertically without imposing any corresponding movement on the other wheel on an axle. The straight axle had been eliminated and replaced with upper and lower A-Frames (control arms) that pivot at the individual wheel position.

Heavy duty tires, for use on forklifts, lowbed trailers, etc.
Industrial solid-A non-pneumatic tire, used most often on forklifts where flats are a constant problem.

The tendency of a body at rest to remain at rest and a body in motion to persist in motion.

See dual mountings.

A tire shaped air chamber, containing a valve and placed inside the tire casing. It seals in the air which supports the load, but is not capable of supporting the load without the strength of a tire and rim surrounding it.

Gear device equally dividing power between axles and compensates for unequal tire diameters.

Mechanical, hydraulic, or pneumatic lifting device to raise chassis for repairs or tire changes.

The trailer over-turns the tractor, pushing the tractor drive wheels sideways, forcing the combination into a V-shaped attitude, resulting in a complete loss of control with no possibility of recovery.

See balance, static.

The intermittent contact of tires in dual as they flex; caused by inadequate dual spacing or by overload.

See gross vehicle weight (GVW).

The load; the freight in a vehicle

Smallest distance laterally between the tire and the nearest fixed point of the vehicle.

A tire assembly that does not run true to its plane; i.e., a damaged wheel moving in a wobbling, side to side manner.

Limiting side movement.

Used in calculating load distribution; it is the distance between the center of the rear axle (or center between tandem axles) and the center of payload.
Negative load base
If center of payload is behind the rear axle, it is negative and takes load off the front axle.

(Distribution of load on truck or trailer chassis.) The relationship of the gross load on the front and rear axles to the total gross load.

Payload on the front axle is equal to the total payload multiplied by the load base (in inches) and divided by the wheelbase (in inches).

FORMULA: Payload front axle =	Payload x Load base
	Wheelbase

To complete the calculation of load per axle, it is necessary to obtain the unladen weight of the vehicle and estimate its breakdown by axle.

A chart in the tire manufacturer's data book listing the carrying capacity of a tire at each of several air pressure increments from the lowest range of practical usage to its maximum capacity.

An index of tire strength which replaces the ply rating system and its predecessor which listed the actual number of plies.

Old	Recent	New
4 plies	4 ply rating (1-2 plies)	Load range B.
12 plies	12 ply rating (1-12 plies)	Load range F.

2,240 Ibs. Also called gross ton.

A low platform trailer for heavy equipment hauling, usually on 15" diameter tires.

Larger cross-section tires for operation at lower pressure. Increased air capacity permits lower pressure.

A unit or combination of units which provides a visible or audible warning signal, whenever the system pressure is below a predetermined value.

Refers to the aspect ratio of a tire; section height is smaller than section width.

Thorough coating of the beads with a vegetable base lubricant is necessary to prevent bead damage and allow for proper bead seating when mounting a tire. Petroleum base lubricants must never be used.