Is there any manga about skateboarding?
Or bycicles and skates..
I've searched for quite some time and never found any.

There's 8, it's about an misterious skate event named "Thirteen Night" and a group of underdogs.Unfortunately it is quite unknown, but it's really good.

It's not exactly skateboarding, but Air Gear is sort of close to roller-blading. Air Treks (the skates) have small engines that give you lift though, coming close to actually flying.

I don't know about any with skateboarding in particular. 8 is the only one that comes up in a search for the word "skateboarding".

If you've ever thought or said "Nice Guys finish last" and really meant it, then you should probably read this LJ post by DivaLion. It's incredibly insightful whether you're male or female.

From a bumper sticker I like:
"If you're gonna ride my ass, at least pull my hair."