Simplify the following text for a Grade 5 native English-speaking person.
Original: Depending on the rules of the class , many types of open-wheelers have wings at the front and rear of the vehicle , as well as a very low and virtually flat undertray that helps achieve additional aerodynamic downforce pushing the car on to the road .
Simplified: Depending on the rules of the class , many types of open-wheelers have spoilers or wings . They are very low and have an almost flat bottom .