Not really big news... and this game is kinda of old so I don't even know if people will care............ but.
If you are on the bicycle, bunny hop on to a car. About 1/10 times you will do it correctly and be in a position where you will not fall off when the driver starts to drive away. When the driver starts to drive away your distance traveled on bicycle will increase and eventually your bike skill will as well.
So bunny hop on to a car, make sure your not falling off and go blaze up a blunt.... when you get back you'll have full bike skill.
Sorry if this has been posted before, just something I thought of the other day.