Why do sports cars want low weight but high down force? It seems contradictory
In: Engineering
Weight is one way to get downforce, but it’s a bad way, because it *also* increases momentum — making it harder to accelerate and harder to decelerate.
Weight is a measurement of mass. It just happens to be “down” on earth. The mass is a component of momentum which you to be as low as possible to allow for improved acceleration.
The lighter the car, then the more acceleration you get with the same force. Also the easier to slow the car (negative acceleration) which is also important in performance vehicles.
Downforce is required because fast vehicles are made aerodynamic by necessity. Going fast and being aerodynamic are the recipe for a wing. If you get lift from the shape of the car then you’re getting less traction, which means you get less forward force from the energy you’re putting into the tires. It’s also dangerous for turning.
Make sense?
The lighter the car, the less energy required to move it. This means you can get more speed out of the same engine if your car is lighter. High down force just means that the car is pressed against the ground, which both prevents the car from flying off the ground due to wind at high speed, but also gives the wheels better traction, which gives the driver more control over the car.
More weight equals less speed. High downforce keeps you from flying off the road when you are going extremely fast. Obviously, it’s a Race, So you want to go as fast as possible. Hence a light car that is held down to the road by air currents.
Downforce caused by aerodynamics is a function of your speed. The faster you go, the more downforce the car experiences. That means at low speeds your car has a lot less downforce – which is fine, you’re not going fast enough to need it.
On the other hand, weight is a function of mass and doesn’t change. The car weighs the same regardless of how fast it’s going*.
So when the car is going 200mph and you need that downforce to get more traction for the turn, you’re not worried so much about accelerating because you’re already going 200mph. Maintaining speed is a lot less costly in energy than accelerating. But when you’re coming out of pit road and need to go fast, having a light car means you can get going very quickly.
At a standstill there is no downforce but also very low air resistance. Getting the car moving quickly depends entirely on power to weight ratio and grip. At speed, drag is he main limiting factor. A little extra weight won’t reduce top speed very much, because t it will make the car take longer to get there. Another big limit is wheels and tires. Cars from the likes of Koenigsegg and Bugatti are pushing g the limits of the speeds we can get a road tire to handle without catastrophically failing. In general making components lighter and stronger lets us push them faster without breaking.
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