No, grip is NOT equal. That's the point. I am sure that Rob would agree that with his aged ATs against me with new Lerma's and equal power and weight, I would surely pull him backwards. You could alter the challenge and just see how far up a bank we could all drive. Grip is the key. OK being able to capitalise on the grip is important, so having super tyres but a one litre engine - you going to lose, but that isn't the case here. We would all have a pretty comparable power to weight ratio.
OK there are all sorts of forces at work here Sam, but where they tyre meets the ground is just about the most critical.
Chris