A few more things/notes I have noticed since experimenting pretty heavily. There may be ways around these "missing" features, but I'm not seeing them. Perhaps you can clear some other things up too :)
1 - Since braking/reverse is a single action, and there is no negative for "speed" of the object (IE, a reverse speed) it's difficult to set maximum speed for reverse while still allowing braking above the desired maximum reverse speed. Any chance of either separating the brake/reverse actions, or applying a negative to a reverse speed?
2 - Moving the car "body" or "chassis" as I have called it, on start of layout, causes some crazy effects. If I want the car to start on a random position and angle on the layout, what's the best way to do this? I have tried setting the X,Y, and Angle of the "chassis" and all of the "wheels" on start. The front wheels seem to be fine, but the rear wheels are usually not present, and come 'flying' in to the car from some random position in the layout.
This also applies some pretty heavy physics forces to the car, sending it driving/spinning away. Setting the chassis to 'immovable' temporarily fixes this problem, but stops the vehicle from appearing at a random X,Y (though the angle is still random).
I have tried ordering when the "carphysics created" from your behaviour takes effect, but it still causes the problem. Any hints/tips?
3 - What does the "topdown car settings - specific settings for topdown car behaviour" option do? I can figure out the rest of the behaviour options, more or less, but that one has me stumped.
4 - Is there a way to 'set' the speed of the vehicle directly? I know you can do a speed comparison (for making shifting gears, etc) but I can't seem to 'set' the speed without applying forces via physics. When the car hits an object, it seems to maintain it's forward momentum, even when it's hard up against a wall or other obstacle. It then takes a while (depending how fast you're driving) until it will reverse, (or go forwards if you've hit the obstacle in reverse). I'd like to be able to do something like "car hits obstacle -> set speed to current.speed - X" in order to quickly scrub off a percentage of the speed.
Again, awesome addition. Hopefully I can figure out some of these minor issues :)