Mud actually dries
Dirt cakes your car as you tear through the mud and even this behaves realistically. In the sun it all begins to harden and turns to flaky dust and, if you then splash through a puddle of water, it will actually wash off. Purely aesthetic, yes, but a beautiful touch.
Wheel life physics
Thanks again to those real world physics, your car's wheels bob and swivel realistically among the muddy tracks you've made. This makes the race tougher, but can also cause tactical bother for the racers behind you. If you make a track near some water, the liquid will actually begin to seep into your tire marks. It's this incredible attention to detail that makes Sega Rally so much more sophisticated than MotorStorm in terms of mud physics.
