Dimensions in GTA 3 & Vice City Handling

There are three settings in the handling.cfg file for GTA 3 and GTA Vice City which are used to set the vehicle’s dimensions:

Official Name Description
c Dimensions.x Width of the vehicle in metres, used for aerodynamic and motion effects.
d Dimensions.y Length of the vehicle in metres, used for aerodynamic and motion effects.
e Dimensions.z Height of the vehicle in metres, used for aerodynamic and motion effects.

I used to think that these did not actually do anything, or that their effect was negligable. However, I have since discovered that the dimension settings have a huge influence on how the vehicle behaves in all circumstances.

What The Settings Do

Using meters as the measurement unit, these three settings draw an invisible box around the vehicle. The dimensions are the full distance for that side rather than being measured outwards in both directions from the middle of the vehicle. The box is used by the game engine to calculate how much resistance the vehicle should have to straight line motion and also to rotation.

If you make all three settings simply 1.0 for any vehicle, you will find that it feels like the car has turned into a beach ball. This is because a small box means there is little resistance to rotation. Also, a small box reduces the friction against straight line movement, allowing a higher top speed.

How to use the Settings

Because the dimensions are in meters, you should try to make them roughly match the real dimensions of the vehicle. This will give a stable starting point for the game to calculate the aerodynamic friction for straight movement and the resistance to rotation. Settings like the centre of mass and the traction bias also have a big effect on how the vehicle will turn but you should normally use the correct dimensions.

The dimensions do not need to exactly match the size of the vehicle and sometimes it can be a good idea to use wrong values on purpose. As shown by my GTA 3 & GTA Vice City Handling: Detailed Acceleration study, a larger mass makes cars reach a higher top speed when the acceleration value remains the same. This means that very light and wide exotic vehicles can end up with a slower top speed than old muscle cars. By using slightly larger settings on the Dimensions.x and Dimensions.y of the off-road vehicle, as well as a slightly smaller value for the Dimensions.z of the exotic vehicle, you can reverse the effect slightly.

Since dimensions also effect the cornering, this technique should be used carefully.