Doubles and Triples
The extra challenge
Pulling two or three trailers amplifies every handling problem: more off-tracking, more sway, and more brake imbalance.
Concepts to master
- Converter dolly: Connects the first trailer to the second. It has its own air lines and must be coupled correctly.
- Rearward amplification: The last trailer swings widest in a turn; the effect grows with speed.
- Brake synchronization: Trailers must be braked so they do not push the tractor. Check that all air lines are connected and the trailer brakes work.
- Crack-the-whip effect: Sudden steering or braking can make the rear trailer swing out.
- Coupling order: Secure the dolly, connect the air lines, and test the brakes before moving.
- Backing: Doubles and triples should be backed only in a straight line, and only when necessary.
Traps
Questions ask which trailer swings widest (the last one), or whether you should back up a set of doubles (avoid it). Another trap: a dolly converter must be secured with its own safety chains or locking device.
Worked example
You are pulling two 28-foot trailers through a right turn. The second trailer's rear wheels track inside the first trailer's path by several feet. You must swing wider than you would with a single trailer, and slow to well below the posted limit to keep the rear trailer from swinging into the adjacent lane.
Rule of thumb
With doubles and triples, drive slower, turn wider, and never back up unless you have no other choice.