The text below is JPS's guide to understanding the collision points in Vehicle's VEH files, originally posted in the Speedsims Forums. It appears after JPS granted permission.
Some people have been asking what the Coll_All, Coll_Player and Coll_Top entries are for in the VEH file.
The 3 sets of entries are coordinates that form 3 shapes around the car. Each shape has 4 corners, thus there are 4 entries for each of the 3 shapes.
A picture is definitely needed here:
* In these pictures the points have been placed in exagerated positions so you can see them better, you would certainly want your collision points to be placed better than shown here.
When one of these points is calculated to be in collision with a solid surface (wall, car, whatever) it is deemed a collision and appropriate damage is calculated (if any) and the physics engine applies the required force against the car and the object the car is colliding with (cone, another car, whatever).
It should be obvious to you at this point that all these coordinates need to be in the correct places otherwise the car will experience collisions when it is not really touching anything yet (point(s) placed too far from the sheet metal) or will experience collisions too late (point(s) place too far inside the sheet metal). Don't ask me how to calculate exactly where these points should be placed for any given car, I'm not that smart, so I just keep tweaking them until all the corners and sides of the car touch against a wall just right.
Coll_Top really comes into play the most when the car flips over or rolls, if this shape is not positioned appropriately then the car might act very strange in a roll and when it's upside down.