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

Think of it this way: when you are giving an engine gas, it has the torque necessary to overcome the numerous fricton losses between different parts. When you don’t give it gas, the engine itself becomes the biggest parasite of the potential power/momentum of the vehicle, and the compound effect of all the other friction losses get stronger and stronger. As for why it continues even after reapplying the gas, you need to know a bit about power bands. Engines typically do not make their maximum power until they hit a certain RPM. When you have had your foot off the gas, and the vehicle has slowed the engine, it takes some time to get the engine back up to the right RPM.