I think each player can set up their own driving assists to their liking, you don't have to use the same settings. Or is that just in split-screen?
Either way, playing without Tire Sim is pointless, especially on 50% and 100% races. One of biggest changes in 2011 is introduction of Pirelli tires which wear out much faster then in 2010, so you'd be missing out on a big (and essential) part of the game.