Ball mount - The part of the hitch system that supports the hitch ball and connects it to the trailer coupler. Ball mounts are available in load-carrying and weight-distributing configurations. An adjustable ball mount allows a hitch ball to be raised, lowered and tilted in small increments to allow fine tuning of the spring bar setup and to compensate for tow vehicle "squat," which occurs after the trailer coupler is lowered onto the ball.

Base Curb Weight (BCW) - BCW is the weight of a vehicle with standard equipment and a full tank of fuel. It does not include passengers, cargo or optional equipment.

BCW  see above

Brake controller - A control unit mounted inside your RV that allows electric trailer brakes to become activated in harmony with the braking of the tow vehicle. This device can be used to adjust trailer brake intensity, or to manually activate the trailer brakes.

Breakaway switch - A safety device that activates the trailer brakes in the event the trailer becomes accidentally disconnected from the hitch while traveling.

Cargo Weight (CW) - The cargo weight includes all the weight added to the Base Curb Weight (BCW), including the passengers, the cargo and any optional equipment. When towing, the trailer tongue weight also has to be included in the cargo weight.

Class A motorhome - An RV with the living accommodations built on or as an integral part of a self-propelled motor vehicle. Models range from 24 to 40 feet long.

Class B motorhome - Also known as a camping van conversion. These RVs are built within the dimensions of a van, but with a raised roof to provide additional headroom. Basic living accommodations inside are ideal for short vacations or weekend trips. Models usually range from 16 to 21 feet.

Class C motorhome - An RV with the living accommodations built on a cutaway van chassis. A full-size bed in the "cabover" section allows for ample seating, galley and bathroom facilities in the coach. Also called a "mini-motorhome" or "mini." Lengths range from approximately 16 to 32 feet.

Coupler - The part of a trailer A-frame that attaches to the hitch ball.

Curb Weight (CW) - Also known as Net Weight. The weight of the RV as it is sitting on the lot, without the personal load you will be adding.

CW   see Cargo Weight  or Curb Weight

Dinghy - A vehicle towed behind a motorhome, sometimes with two wheels on a special trailer called a tow dolly, but often with all four wheels on the ground.

Dry Weight (DW) - The weight of the RV without adding fuel, water, propane, supplies and passengers. The manufacturers UVW will not include any dealer-installed options. Also known as Unloaded Vehicle Weight.

Dually - A pickup truck, or light-duty tow vehicle, with four tires on one rear axle.

Dullies - Dual Tires.

DW   See Dry Weight

Engine oil cooler - A heat exchanger, similar to a small radiator, through which engine oil passes and is cooled by airflow.

Fifth-wheel trailers - Fifth-wheel trailers are trailers designed to be coupled to a special hitch that is mounted over the rear axle in the bed of a pickup truck. These trailers can have one, two or three axles and are the largest type of trailer built. Because of their special hitch requirements, fifth-wheel trailers can only be towed by trucks or specialized vehicles prepared for fifth-wheel trailer compatibility.

Frame-mount hitch - Class II and higher hitches are designed to be bolted to the vehicle frame or cross members. This type of hitch may have a permanent ball mount, or may have a square-tube receiver into which a removable hitch bar or shank is installed.

GAW   See Gross Axle Weight

GAWR   See Gross Axle Weight Rating

GCW   See Gross Combined Weight

GCWR  See Gross Combination Weight Rating

GTW  See Gross Trailer Weight

GVW   See Gross Vehicle Weight

GVWR   See Gross Vehicle Weight Rating

Gross Axle Weight (GAW) - The total weight supported by each vehicle's axle (front or rear). To obtain this number, you have to weigh the vehicle and the trailer on a scale.

Gross Axle Weight Rating (GAWR) - The manufacturer's rating for the maximum allowable weight that an axle is designed to carry. GAWR applies to tow vehicle, trailer, fifth-wheel and motorhome axles.

Gross Combined Weight (GCW) - The actual weight of a vehicle and trailer combined. To obtain this number, you have to weigh the vehicle and the trailer together on a scale.

Gross Combination Weight Rating (GCWR) - The maximum allowable weight of the combination of tow vehicle and trailer/fifth-wheel, or motorhome and dinghy. It includes the weight of the vehicle, trailer/fifth-wheel (or dinghy), cargo, passengers and a full load of fluids (fresh water, propane, fuel, etc.).

Gross Trailer Weight (GTW) - Gross trailer weight is the weight of the trailer fully loaded in its actual towing condition. GTW is measured by placing the fully loaded trailer on a vehicle scale. The entire weight of the trailer should be supported on the scale.

Gross Vehicle Weight (GVW) - The actual weight of a vehicle when fully loaded. (Base Curb Weight + Cargo Weight)

Gross Vehicle Weight Rating (GVWR) - The total allowable weight of a vehicle, including passengers, cargo, fluids and hitch weight.

Hitch ratings - Hitches are rated by the manufacturers according to the maximum amount of weight they are engineered to handle. Class I travel trailer hitches are rated for towing as much as 2,000 pounds. Class II units are for loads up to 3,500 pounds. Class III has a rating of 7,500 pounds, and Class IV is for loads of up to 10,000 pounds. Class V hitches are designed for towing loads up to 14,000 pounds. These ratings may vary depending on the manufacturer. Fifth-wheel ratings range to 25,000 pounds. The weight rating refers to the total weight of the trailer/fifth-wheel, with freshwater tank full, propane tanks full, all supplies on-board and ready to travel.

Hitch weight - The amount of weight imposed on the hitch when the trailer is coupled. Also referred to as "tongue weight". Hitch weight for a travel trailer can be 10-15 percent of overall weight; fifth-wheel hitch weight is usually 18-20 percent of the overall weight.

Light Weight RV - RVs that are designed to be easily towed behind most Minivans, light-duty trucks and cars! The most common being a pop-up trailer.

Maximum Loaded Trailer Weight - The maximum allowable fully loaded weight of a trailer. (GCWR - GVW).

Net Carrying Capacity (NCC) - The amount of cargo, passenger and fluid weight that can be added to an RV without exceeding its GVWR. The NCC label in an RV may not include the weight of dealer installed or factory installed options already on the vehicle. Subtract UVW from the GVWR and the result is what can be added to the factory weight.

Receiver - The portion of a hitch that permits a hitch bar or shank to be inserted. The receiver may be either 11/2-, 15/8- or 2-inch square; the smallest being termed a mini-hitch.

Safety chains - A set of chains that are attached to the trailer A-frame and connected to the tow vehicle while towing. Safety chains are intended to keep the trailer attached to the tow vehicle in the event of hitch failure, preventing the trailer from complete separation. They should be installed using an X-pattern (criss-crossed) so the coupler is held off the road in the event of a separation.

Shank - Also called a hitch bar or stinger. A shank is a removable portion of the hitch system that carries the ball or adjustable ball mount, and slides into the receiver.

Spring bar - Component parts of a weight-distributing hitch system. The spring bars are installed and tensioned in such a manner as to distribute a portion of the trailer's hitch weight to the front axle of the tow vehicle and to the axles of the trailer.

Sway - Refers to the "fish-tailing" action of a trailer caused by external forces that set the trailer's mass into a lateral (side-to-side) motion. The trailer's wheels serve as the axis or pivot point. . Also known as "yaw".

Sway control - Devices designed to damp the swaying (fish-tailing) action of a trailer, either through a friction system or a "cam action" system that slows and absorbs the pivotal articulating action between tow vehicle and trailer. The most common device in use is a "sway bar".

Tail swing - All motorhomes built on chassis with short wheelbases and long overhangs behind the rear axle are susceptible to "tail swing" when turning sharply. As the motorhome moves in reverse or turns a corner, its extreme rear can move horizontally and strike objects nearby (typically road signs and walls). Drivers need to be aware of the amount of "tail swing" in order to prevent accidents.

Tongue Weight (TW) - The amount of weight imposed on the hitch when the trailer is coupled. Also referred to as "hitch weight". Tongue weight for a travel trailer can be 10-15 percent of overall weight; fifth-wheel hitch weight is usually 18-20 percent of the overall weight.

Tow bar - A device used for connecting a dinghy vehicle to the motorhome when it's towed with all four wheels on the ground.

Tow rating - The manufacturer's rating of the maximum weight limit that can safely be towed by a particular vehicle. Tow ratings are related to overall trailer weight, not trailer size, in most cases. However, some tow ratings impose limits as to frontal area of the trailer and overall length. Tow ratings are determined by the vehicle manufacturer according to several criteria, including engine size, transmission, axle ratio, brakes, chassis, cooling systems and other special equipment.

Trailer brakes - Brakes that are built into the trailer axle systems and are activated either by electric impulse or by a surge mechanism. The overwhelming majority of RVs utilize electric trailer brakes that are actuated when the tow vehicle's brakes are operated, or when a brake controller is manually activated. Surge brakes utilize a mechanism positioned at the coupler that detects when the tow vehicle is slowing or stopping and activates the trailer brakes via a hydraulic system.

Transmission cooler - A heat exchanger similar to a small radiator through which automatic transmission fluid passes and is cooled by airflow.

Travel trailer - Also referred to as "conventional trailers" these types of trailers have an A-frame and coupler and are attached to a ball mount on the tow vehicle. Travel trailers are available with one, two or three axles.

Umbilical cord - The wiring harness that connects the tow vehicle to the trailer, supplying electricity to the trailer's clearance and brake lights, electric brakes and a 12-volt DC power line (to charge the trailer's batteries).

Unloaded Vehicle Weight (UVW) - The weight of the RV without adding fuel, water, propane, supplies and passengers. The manufacturers UVW will not include any dealer-installed options. Also known as Dry Weight.

Weight carrying hitch - Also known as a "dead-weight" hitch, this category includes any system that accepts the entire hitch weight of the trailer. In the strictest sense, even a weight-distributing hitch can act as a load-carrying hitch if the spring bars are not installed and placed under tension.

Weight distributing hitch - Also known as an "equalizing" hitch, this category includes hitch systems that utilize spring bars that can be placed under tension to distribute a portion of the trailer's hitch weight to the tow vehicle's front axle and the trailer's axles.

Wet weight - The weight of the vehicle with the fuel, freshwater and propane tanks full.

Wheelbase - The distance between the center lines of the primary axles of a vehicle. If a motorhome includes a "tag" axle, the distance is measured from the front axle to the center point between the drive and "tag" axle.

Yaw - Refers to the "fish-tailing" action of a trailer caused by external forces that set the trailer's mass into a lateral (side-to-side) motion. The trailer's wheels serve as the axis or pivot point. Also known as "sway".