On cars with manual transmissions, when in low gear (typically 1 or 2), why does accelerating and then taking your foot off the gas make the car lurch forward with that uneven, jerking motion?

Question

Why wouldn’t the car just decelerate smoothly when you take your foot off the gas? And why does it often continue even if you step on the gas again?

In: Engineering

Answer 1

In all transmissions, a clutch connects and disconnects the engine (power) from the gearbox (shifter) and drivetrain (wheels). In automatic transmissions, a computer makes that connection and disconnection very smooth when shifting into other gears, so it’s hard to notice any jerk because it won’t stay in the same gear longer than it should. If you put an automatic transmission into low gear (L or 2), you’ll feel similar jerkiness. If you press the clutch pedal in a manual transmission at the right times, it will feel smooth too.