How the crap do I get top times in all the courses???? Some of them seem IMPOSSIBLE!!!!! Any bike upgrade/handling tips???

Get all the bike upgrades from the bike guy. Then you'll be able to top some bike missions, and by doing that you'll be awared new bike parts to make you able to complete the other bike missions.
Otherwise just practice taking shorter corners and fewer turns to lower your time.

you can find bike parts in some areas but its compleatly random just try your luck and see what happens

Making a complete U-Turn on certain maps can save you a large amount time. Once you get a King Chim during certain courses, map a complete U-Turn, which be turning around and going the way you came. This type of tactic good for certain maps, just looking at a map, you can which maps this tactic is good for.

There's 10 courses, to my knowledge, total. The easiest of the bunch tend to be the courses in the desert. Defeating those courses aren't too difficult. Then just keep upgrading your bike. If you're not on Volume 3, it's advised to finish the bike courses as soon as possible, then you can receive good items earlier than usual.

Or you could use the cheap way to do it and press O when your about to hit a King Chim Chim, which is a sort of glitch which makes you automatically beat the course. I did this for the bike missions, just cause they were too much of a hasstle.