Ohio CDL Combination cheat sheet

Combination Vehicle Knowledge (Ohio CDL)

• A combination vehicle's pivot point is the rear axle of the tractor; the trailer's wheels off-track inward during a turn, so the trailer cuts the corner - swing wide and watch the trailer tires in the mirrors.

• The tractor protection valve closes and cuts air to the trailer when trailer air pressure drops below roughly 20-45 psi, or when the trailer-supply (emergency) line separates, applying the trailer spring brakes.

• Coupling order: inspect the fifth wheel and kingpin, back under with the trailer brakes locked, listen for the click, tug-test twice, visually confirm the jaws closed around the kingpin, then connect air lines and electrical cord.

• The trailer-supply line is the emergency line (often red); the service line (often blue) carries the brake-application signal. Crossed lines leave trailer brakes released or dragging - always check with the hand valve after coupling.

• Uncoupling: park on level ground, chock the trailer wheels, lower the landing gear to firm ground, disconnect lines and cord, release the fifth-wheel locking lever, then pull the tractor slowly forward.

• Off-tracking means the rear wheels of the trailer follow a path inside the tractor's front wheels; the longer the wheelbase and the sharper the turn, the greater the off-track and the more room needed.

• Total stopping distance equals perception distance plus reaction distance plus brake lag plus effective braking distance - air brakes add lag time, and a loaded combination needs far more distance than a bobtail.

• Rearward amplification causes the last trailer in a multi-trailer set to swing wider than the tractor during quick lane changes; steer smoothly and avoid abrupt maneuvers at speed.

• When backing a combination, hold the bottom of the steering wheel and turn toward the side you want the trailer to go; use a spotter and GOAL (get out and look) when unsure.