Physics: What Affects Speed in Vehicles?

Note: The following article was written by Ritesh Arunkumar Y9.

People love fast cars, including me, but what actually makes these cars go fast is a topic that only a few know properly. People think it's just all about the engine, but the magic is all about how the whole car works together, like the San Antonio Spurs, who won the NBA championship in 2014, with the main reason being that they worked together better than anyone else.

1. The Shape and Body

The shape of the vehicle affects speed greatly, as based on the shape, the airflow moves differently around the car, creating more or less of the pushback effect, which is when a car moves, it has to push the air particles out of the way, creating an opposing force known as drag. The boxier or taller a car is, the more drag it has, so it has to move more air particles, which causes a bigger opposing force, making the car slower. This is where a car's body can be more aerodynamic to reduce the opposing force by creating a sleeker design. That is why most fast cars have wings and are quite short. The body can also be lighter, which means there is less weight that the car needs to move. Things like wings, spoilers and splitters help push the car down by creating downforce, but to access the absolute maximum speed, you want the least amount of drag.

2. The Powertrain

This is where the main teamwork happens, with many components, including the engine, gearbox, driveshaft and more. It has two main parts, with the engine and electric motor generating the power while the drivetrain uses the power to move the car. The main part of the drivetrain that affects speed is the transmission, which has gears that you can change between, but the limit is that the engine can only rotate safely within a specific range. This is measured in RPM (revolutions per minute), which means how many times it rotates per minute. But to reduce this limitation, cars have different gears that act differently. For example, low gears make use of pulling power (torque), as the engine spins quickly, but the wheels still move slowly. This is a big part of moving from a dead stop. Higher gears allow the wheels to spin very quickly but reduce the RPM of the engine to be more fuel-efficient. The whole drivetrain affects speed as it changes the speed of the engine and how it reaches the wheels, and the whole powertrain affects it, as the more power it generates, the faster the speed will be.

3. Other Effects

Many other things affect the speed of a vehicle, some more than others. Tyres play a big role, as if you have a great powertrain but the wheels lack grip, you will spin your tyres and not reach the maximum speed. Wide tyres provide lots of grip but cause more friction, which could reduce some top speed. A main example is the power-to-weight ratio. It is well known, as it shows why the engine is not the only thing that matters, as a light car with a normal engine could be faster than a big SUV with a V8. But the heavier certain parts are, the more the speed is affected, as the things the car has to spin, like tyres, can affect the speed more than if the body is heavier, as it needs more power to spin the tyres enough to get up to speed. An effect that is quite small but can hugely affect speed results is the environmental conditions, as wet or icy conditions create less grip, and the air can affect it, as cold air is denser than warm air, which means the engine can burn more fuel, generating more power, but can create a bit more drag. And if the air is thinner, the engine takes in less oxygen, which means it won't generate as much power, losing potential extra speed.

Conclusion

Overall, I feel as though, as important as the engine can be, it needs the rest of the car to extract all of the speed possible. The power-to-weight ratio and environmental conditions will always affect it, and it may be impossible to find 100% of the top speed of a vehicle, as getting everything perfectly right to the best ability and having the best conditions to run in has a tiny probability of occurring. Some factors may affect speed more than others, but everything still affects the speed, so don't overlook a small detail, as even that could alter the result you get.