Originally Posted by Piobaire
If you want to say that your initial statements were incomplete, and you meant to differentiate between total potential traction vs. usuable traction, I'll agree.
Sorry about that. It's easy to fall into shorthand.
This way it can be seen that an AWD vehicle will have 100% more traction available than a 2WD vehicle, all other things being equal.
It isn't clear what you mean by all other things being equal. To me, it means you are placing two identical cars on identical road surfaces, and the only thing you're changing is the drive system, in which case what you say is false. Consider 3 cases: 1. The trivial one: your front tires have a smaller contact patch than the rears. 2. Your rear tires are on ice, and your front tires are on dry asphalt. Consider the reverse too. 3. One side of your car is on ice while the other side is on dry asphalt. In none of those cases will AWD have 100 percent more traction than 2WD. In all cases, your traction is limited by your tires.
Note the three things, two related, one the opposite. The middle one, stoppage, is about braking, which as I've already pointed out is a red herring in this conversation over transmission type efficacy. "Traction" has as a component of its definition the ability to transfer power that causes movement, in the relevant portion of this discussion.
Tires transmit force to the ground by their traction. "Force" is used in the physics, F=ma sense. That force can be effected by three things in a car: 1. Pressing the gas pedal. 2. Pressing the brake pedal. 3. Turning the steering wheel. From a physical standpoint, it's basically the same phenomena, just in different directions. There's nothing particularly special about one or the other. It is the ground's reaction to that force (Newton's 3rd law) that causes a car to move forward, slow down, or rotate. Having said that, I still don't understand why braking is a red herring. It was claimed that AWD is better and safer in snow, and all else being equal it is, but I wanted to remind everyone not to forget about the other things you have to do while driving. Too often, people think that AWD is the most important thing to get when driving in snow, when really it's the tires, and the reason is because AWD can't help you brake better or turn in better.
Further, all situations are "traction-limited situations" since the total amount of traction is always going to be finite.
Sorry about the shorthand again. When I say "traction-limited" I mean those situations in which you are operating close to the traction limits of the tires --- when you have more power than traction, for example. --Andre