So, I recently watched Nerd3's video about Carmageddon, and it blew my mind how hilarious he made it. Alas, some of the questions and theories he uttered during the video are unanswered and a tad off, so I'll now let you in on the mechanics behind the Carmageddon mod.
Many of you know that the Carmageddon mod is simply setting the friction bias on the tires to -9 (or equivalent) for all the cars. There's nothing more I've done to the game than this specifically. Thing is, this makes for some extraordinary results when the game runs, as the friction bias is a value used by the game to tweak the base friction of the tires by a certain amount given certain conditions. This is mostly speculation and reverse-engineering at hand, so do correct me if I am wrong at some point.
The stock values are usually 0.46 and 0.47 (if I remember correctly), and they do not differ a whole lot from each other. Set the bias to 0, and the cars slide around like they're on ice. set it to above 1, and they also slide around like on ice. Set it to a negative value, and the tires push the car onwards instead of slowing them down. The higher the number, the harder they push, obviously, but what people don't know is that the cars gain more speed the faster they go. This has an interesting effect when they reach Bullet's (the physics engine in the game) clamping limits on the real-time calculation (e.g. where the game decides to do a sloppy job to keep the framerate high instead of prioritizing physics quality), and the cars go through walls, the ground, and in the air, as if they were still driving on road. The exact specifics regarding this I am unsure of, but it's one of the little quirks that makes Carmageddon such a messy chaos, and I hope it carries on to GTAV.
On to the difference between cars, bikes and helicopters: Cars are easy. All cars in the game are eligible for Carmageddoning, as are bikes and helicopters (sorta). All three vehicle types have the bias value, but helicopters (as far as I know) do not use it because none of the copters in the game has wheels (just struts), yet the values for tire traction is in the handling.dat for them as well. Applying Carmageddon to bikes is boring. Extremely boring; they just tip over, and that's it. Nothing more. They are unrideable, and just tip over given any possible opportunity, and just lie there, completely uninteresting. Thus, I have not enforced Carmageddon upon them.
Contrary to popular beliefs, the cars are not scripted to home in towards the player. That's just you being (un)lucky. And standing on an overturned car's tires won't do anything, since the tires' friction is towards geometric faces (i.e. everything NOT people and weapons lying on the ground). Yes, this means they can, and will (gleefully) "drive" on the side of buildings.
I defined which cars are affected by Carmageddon and which ones are not quite some time ago, and I can only remember excluding the GT and the Infernus from the mass. I excluded some others as well, possibly 5 or 6 in total, but I don't remember which. I'm a lazy ass, but I believe I wrote it in the readme that comes with Carmageddon.
Hope that clears some of the facts up (except for the speculation part). It's too late at night here for me to proof-read this and realize how excessively messy it is at the moment.