So in the real world there is air. Air acts as drag for vehicles, and so the cars are curved to be as fuel efficient as possible. Adding a aerodynamics tester in the game will allow users to improve their overall aerodynamics for the vehicle to go more faster and have more faster acceleration. And will allow to see which parts are the least aerodynamic and parts that are super aerodynamic. Adding a drag coefficient would be beneficial to the game itself also. Adding fluid physics would make it more challenging for people to make a very fast vehicle.
Here are examples of what i mean with this very insane suggestion as an addict to aerodynamics:
A person gets a truck and attaches a booster to it and expects it to be 300-500MPH fast. But he realizes he only gets 235MPH because of his very brick front aerodynamics. So he later curves it and makes it more angled and then he manages to hit 450MPH.
A person who is willing to challenge himself will use the aerodynamics tester to get the most curviest car in the game to have the fastest acceleration and get a very top speed.