Mass

Mass is the weight of the vehicle. Mass gives you an advantage to plow through heavy traffic and other obstacles. Larger vehicles are massive and durable.

Overview
It is measured in a unit known as the gross vehicle weight rating (GVWR), or gross vehicle mass (GVM) is the maximum operating weight/mass of a vehicle as specified by the manufacturer including the vehicle's chassis, body, engine, engine fluids, fuel, accessories, driver, passengers and cargo but excluding that of any trailers.

The vehicle's mass can affect the car's handling, durability, and speed. If the mass of a car is lighter, then it has a weaker durability and it could effect handling as well. One of the lightest cars in the game is the Panoz GTR-1. Its weight is 2,130 lbs.