The phrase "to drop a gear" means changing to a lower gear while driving, usually to increase speed or power.
Sentences with «to drop a gear»
Surely, though, no one will miss the six because this car is quick off the line and quick to drop gears with that dual - clutch transmission. (autoweek.com)
On the downhill sections, the tow / haul mode really helped by dropping gears to slow the load. (autoweek.com)
You can, however, use paddles behind the steering wheel to drop gears manually to improve acceleration. (carbuyer.co.uk)