Cars can't make it up steep hills in grassy areas, even in 1st gear. Cars can't make it up dirt roads if there is a steep hill, even with a run up of 40 mph and driving in a low gear. Driving up hills on main tarmac roads can be slow but manageable, however the dirt/mud track roads cars cannot make it up the hills at all. Maybe cars would be better with a boost, give the cars a bit more power in low gears or more traction with the ground on dirt roads and grass so they can move slow but can still move and are not completely stuck.