Compared with "", graphics are greatly improved with more detail on cars and tracks (despite running on the same PlayStation 2 hardware). The physics are also greatly improved, with the major upgrade that cars now experience body movement, such as pitching (forwards and backwards rolling) under braking. Barriers have considerably more friction to slow down the cars in GT4 (in an attempt to stop the use of "wall riding"), but there is minimal friction between cars, so the advantage obtained by running into the side of another car (instead of braking) is still present. Each of the Driving Missions and Special Conditions events give a 5-second penalty for hitting the walls or opponents' cars in this way, where the car's speed is restricted to 50 km/h (31 mph) until the timer disappears when it reaches zero.