How the handling works
The car is a bicycle model, the same idea most racing games use under the hood. The front and rear tyres each have a slip angle: the difference between where the tyre points and where it is actually going. A tyre pushes back harder as its slip angle grows, up to the limit of its grip, and then it slides. When the front runs out of grip first the car understeers and runs wide. When the rear runs out first the car oversteers and the back swings out. That is a drift.
What each setting does
Top speed, acceleration and brakes set the straight line numbers, shown below the drive view as a 0 to 100 km/h time, a top speed and a 100 to 0 braking distance. Steering angle is how far the front wheels turn at low speed. It shrinks as the car goes faster, like in most games, so the car stays stable on a straight. Steering speed is how fast the wheels get there. Front and rear grip set where the limit is on each end. Drift sets how much the handbrake and full throttle cut the rear grip. Weight makes the car slower to rotate and softer on its tyres. Slide assist turns the front wheels into a slide for you and pulls the nose back past about 30 degrees, so a player can hold a drift without spinning.
Testing it
The drift pad is an open square with cones, good for donuts and figure 8s. The test track is a short loop with fast and slow corners. My track loads the last track you made in the Racing Track Builder, and that tool drives with the car you save here. Change the surface to see the same car on dirt, snow or ice. Switch to 3D to drive from a chase camera with body roll, smoke and skid marks, and press C for a closer or wider view. Arrows or WASD drive, Space or Shift is the handbrake for drifting. Skid marks show where each tyre slides, the graph shows speed and slip angle for the last ten seconds, and the drift score counts how long, how fast and how sideways you hold a slide.
Using it in your game
The JSON file holds your settings and works with any engine. The Pro kit has the handling maths as a small class for Godot 4 and for Unity, plus a controller for a 2D top-down car and for a 3D car on each engine. The controllers read the arrow keys or the default input axes, use the engine's own collisions for walls, and feed the result back into the model, so the car feels the same as it does here.
Can I use it commercially?
Yes. Your settings and the exported scripts are yours to use in free and commercial games.