$40 saves u punching a hole through your case thats if your worried about it i have heard a few big rocks hit the motor on our bikes even the missus has heard it aswell so it doesnt matter wether u ride like a sissy or flat out
in the bush its cause from alot of people using the same lines also 4wd's make alot of ruts on sloppy days after there has been alot of rain and the water needs to run somewhere as the water runs down hills it follows the same path washing away the soil leaving ruts once its started they only get bigger and deeper here in sydney "menai" there are some ruts from rain and 4wd's that can swollow your mini bike