General hints:

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Manual gear shift is the best way to use the advantage of full engine controll e.g.  using the engine brake by shifting down to drive turns easier. You have to get used to it but soon you won't be able to drive without it.
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You shouldn't forget that you can use your brake. In front of a turn you should brake and shift down at the same time. That way you can drive sharp turns
very fast without leaving the road.
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You can charge your cannon by holding down the fire key. If you fire and hit, your enemy will loose half of its energy with only a single shot.
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Almost every track has more than one shortcut. Often you can jump over a long distance saving a large amount of time.
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If your car is headed "wrong way" drive off the track maybe even down a cliff to save time turning around.

Championship:

To receive continues you have to win every track with the first place or your team must win the team ranking at the end of a season. You shouldn't use continues during the first seasons, later ( in the Titan class ) it is very important to have as many continues as possible.

You shouldn't kill the drivers of your team. They don't shoot at you and you can get a continue if your team wins the team ranking.

Sometimes it's more clever to kill an enemy than to overtake him.

Cheats:

Press and hold Shift + Ctrl + C on the main screen to open the CHEATS option. On the Cheats Screen, type one of the following:

GLOBAL
all tracks are selectable
DEV 6
all cars are selectable
RACE CORPS
all seasons are selectable in Championship Mode
TATSU MAKI
higher fire frequency
PEP!
all powerups are nitros
H-PLUS
undistructable