Bike obstacles
Within the cource of the Pokémon generations there have been many bike-exclusive areas and obstacles to surpass.
Obstacles
Cracked floor-This can only be surpassed with a fast bike. If you slow down or walk you will fall through the floor. These only have appeared in generation 3
Muddy slope-This can only be passed with a fast bike.If you attempt to walk up or use a slow bike you will just slide back down. You will also slide down if you stop on the slope before you go all the way up. These are found in both generation 3 and 4.
Bike bridge-These vary between generation 3 and 4. In generation 3 you could only use a slow bike to get accross because you would need to do a side hop trick. Because the trick option was eleminated in gen. 4 both speeds would work.
Ramp-You can only get accross this with a fast bike. If you bike into this from a distance you will be shot a distance. These are only found in gen. 4.
Bikeless areas
There are many places in the Pokémon games where you aren't allowed to use bikes.
Extra tall grass
Snow
Mud
Muddy grass
Buildings
water
Bike only areas
There are some areas in the games wnere you can only use bikes.
cycling road