Truck Trailer Glossary
AXLE-The shaft that attaches wheels to trailer. One, two, and three axles are sometimes referred to as single, tandem, and triple axle set-ups respectively.
BALL- the trailer ball is what attaches the trailer to the hitch. Ball sizes vary as do capacities by manufacturer. Balls also come in many different finishes. For simplicity, we only use chrome finish balls, except for the heat treated balls which have a raw finish.
1-7/8" ball with 3/4" or 1" shank: 2000# Capacity
50mm ball with 19mm shank: (European applications only)
2" ball with 3/4" shank: 3500 or 5000# capacity
2" ball with 1" shank: 5000 or 6000# capacity
2" ball with 1-1/4" shank: 6000, 7500 or 8000# capacity
2-5/16" ball with 1" shank: 6000# capacity
2-5/16" ball with 1-1/4" shank: 10,000# capacity
2-5/16" ball with 1-1/4" shank(heat treated): 14,000, 24,000, or 30,000# capacity
3" ball with 2" shank (gooseneck only): 30,000# capacity
BRAKE CONTROLLER -- A control unit mounted inside the vehicle 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.
BUMPER-MOUNT HITCH -- This type of hitch is available in two configurations: A bracket with a ball mounted to the bumper or a ball is attached to the bumper (typically on pickup trucks). These hitches have very limited RV applications.
Chassis -- The main structure or frame of the vehicle. Other parts get attached to the chassis i.e. truck fenders and a truck cab or a trailer enclosure attaches to the chassis.
CLASS 1 -- A trailer Hitch with capacity of up to 2000# gross trailer weight and 200# tongue weight.
CLASS 2 -- A trailer hitch with capacity of up to 3500# gross weight and 350# tongue weight.
CLASS 3 -- A trailer hitch with capacity of up to 5000# gross and 500# tongue weight. Also sometimes refers to a hitch with a 2" receiver regardless of rating.
CLASS 4 -- A trailer hitch with capacity of up to 10000# gross trailer weight and 1000-1400# tongue weight. Although many times any hitch with a capacity greater than 5000# gross weight is referred to as a Class 4.
Class 5 -- A Trailer hitch with capacity greater than 10000# gross trailer weight and 1000-1200# tongue weight. Usually a 2.5" receiver or in some special cases a 2" receiver.
-- Often a bumper like a "V" to lower the step surface in the center and lower the hitch height. See Nixon.
DW -- Dry weight. The manufacturer's listing of the approximate weight of the RV with no supplies, water, fuel or passengers.
EQUALIZER -- A colloquialism for a Weight Distributing Hitch
FIFTH-WHEEL TRAILERS -- Fifth-wheel trailers are 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.
GAWR (Gross Axle Weight Rating) -- 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.
GCWR (Gross Combination Weight Rating) -- 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.). GTWR (Gross Trailer Weight Rating) -- Maximum allowable weight of a trailer, fully loaded with cargo and fluids.
GOOSENECK TRAILER -- The gooseneck trailer employs a pivoted coupling arm which attaches to a ball mounted in the bed of a pickup truck. The coupling arm connects to the hitch mounted over the rear axle in the truck bed.
HITCH RATINGS -- Hitches are rated by the manufacturer 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 based on class category 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/fifth-wheel is coupled. Sometimes referred to as conventional trailer "tongue weight." Hitch weight for a travel trailer can be 10-15 percent of overall weight; fifth-wheel hitch weight is usually 18 to 20 percent of the overall weight.
JACK KNIFE --To place the trailer at a very sharp angle to the tractor.
KINGPIN -- Anchor pin at the center of a semitrailer's upper coupler which is captured by the locking jaws of a tractor's fifth wheel to attach the tractor to the semitrailer.
LIFT AXLE -- Extra, unpowered axle needed only when the vehicle is loaded, allowing it to meet federal and state vehicle weight standards. The lift axle is mounted to an air spring suspension that raises the axle when it is not required.
LOWBOY -- An open flat-bed trailer with a deck height very low to the ground, used to haul construction equipment or heavy loads.
PAYLOAD CAPACITY -- The maximum allowable weight that can be placed in or on a vehicle, including cargo, passengers, fluids and fifth-wheel or conventional hitch loads.
RETARDER -- Device used to assist brakes in slowing the vehicle. The most common type of retarder on over-the-road trucks manipulates the engine's valves to create engine drag. (This type is commonly referred to as "Jake Brake" because the predominant manufacturer is Jacobs Vehicle Equipment Co.) Other types of retarders include exhaust retarders, transmission-mounted hydraulic retarders and axle-mounted electromagnetic retarders.
SAFETY CHAINS -- A set of chains that are attached to the trailer A-frame and must be 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, so the coupler is held off the road in the event of a separation.
SHANK -- Also called a hitch bar or stinger, the 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.
STINGER -- See shank.
SWAY -- Fishtailing action of the 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 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.
TAG-A-LONG TRAILER -- A trailer that is pulled behind a vehicle with a chassis mounted trailer hitch as opposed to a Fifth-Wheel or Gooseneck.
TAIL SWING -- 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, the extreme rear of the coach 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.
TANDEM AXLE -- A two axle trailer also known as dual axle.
TONGUE WEIGHT -- The amount of weight imposed on the hitch when the trailer is coupled. See "hitch 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 that is positioned at the coupler, that detects when the tow vehicle is slowing or stopping, and activates the trailer brakes via a hydraulic system (typically used on boats).
TRAVEL TRAILER -- Also referred to as "conventional trailers," these types of rigs 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. Depending upon tow ratings, conventional trailers can be towed by trucks, cars or sport-utility vehicles.
UVW (Unloaded Vehicle Weight) -- Weight of the vehicle without manufacturer's or dealer-installed options and before adding fuel, water or supplies.
UTQGL (Uniform Tire Quality Grade Labeling) -- A program that is directed by the government to provide consumers with information about three characteristics of the tire: tread wear, traction and temperature. Following government prescribed test procedures, tire manufacturers perform their own evaluations for these characteristics. Each manufacturer then labels the tire, according to grade.
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.
YAW -- Fishtailing action of the 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."
Truck Trailer Glossary 8/02/05