Do you know why you won't see a truck on a racetrack?
The answer is pretty simple since they are way too big for the racetrack. Another possible explanation is that it would cause too much damage since there are many racers getting an accident and the sponsors can't afford an accident. Imagine the chaos the trucks would bring if the driver can't handle it anymore. And this is possible since a truck is much more difficult to maneuver compared to a regular vehicle. They might have the power and the speed, but such speed would only bring chaos on the road.
Drive your truck as fast as you can till you reach the finish line. There are other vehicles on the road, which means that there would be lots of potential accident if you collide with the other vehicles. Fortunately, that is not this game is created and you can drive your vehicle as safely as you want it to be. This game is just concern about speed, so drive your truck as fast as you can. Perform some stunts while you are up on the air. Try to fulfill the requirement of each level. You will earn after every level and you can use it to buy some upgrades or buy a better vehicle.