Fast, fun to drive and intimidating. Those are the characteristics sports car owners expect when spending their hard earned money. However, what are the basics of vehicle architecture that ensure these characteristics?
Designing a sports car
Building a car is like bringing together several attributes and then compromising to get them all to fit. Most people will agree that the Holy Grail of sports car design is achieving optimal vehicle architecture and the best compromise between power vs. weight (power/weight ratio). However, aerodynamics aside, the most important factor when looking at the performance of a sports car is weight. Lightweight not only makes the car go faster, it saves fuel, it submits the vehicle to lower loads, it simplifies and optimises suspension design and it simply delivers a great driving experience.
Naturally, the idea is to position the masses on the car vertically, as low as possible and as close to the middle on the longitudinal direction. The weight transfer during cornering and acceleration is proportional to the centre of gravity (CG) height of the car. Sometimes, manufacturers decide to make their sports cars more challenging to drive by biasing the weight rearwards (e.g. 40:60 weight distribution) .
When the vehicle is under cornering the grip on the tyres will be reduced and uneven. The higher the CG, the longer it will take the vehicle to return to the optimum position and recover grip. This is why sports cars are always low.
Vehicle drivetrain design – a vehicle architecture fundamental
In summary, there are four types of drivetrain design you will find in typical vehicle architecture (not considering all wheel drive): front engine + front wheel drive, front engine + rear wheel drive, mid engine + real wheel drive and rear engine + real wheel drive. Nowadays, as much as technology allows engineers to correct the flaws of each configuration, you can’t fight physics.
Front engine + front wheel drive
When a vehicle is under acceleration, its inertial forces will see weight transferred to the rear. That topic could easily be the subject of another article on its own, but when a tyre is submitted to higher loads it increases its grip capacity. In this case, more load on the rear tyres means more acceleration capacity on the rear tyres. Therefore, a front wheel drive vehicle architecture means wasting the tyres acceleration capability.
So why is this configuration of vehicle architecture often used? Mounting the engine, transmission and driveshaft in the front presents not only the cheapest solution but it allows for a much greater space for occupants and simplifies the design of the car.
Front engine + rear wheel drive
Mounting the engine on the front and driving the rear wheels is a good compromise between performance and practicability. This design allows engineers to take advantage of the better performance of rear wheel drive while maintaining a good space for occupants and their luggage. Since this configuration requires a driveshaft across the whole body of the car, the disadvantages are an increase in complexity, added weight and cost. Although a weight distribution of 50:50 is easily achievable, the vehicle has significantly more mass on the rear axle. This leads the car to a common instability effect on tight corners (oversteer).
Mid engine + Rear wheel drive
This is the type of vehicle architecture you will find on most supercars (also mid engine + all wheel drive). It applies the higher masses of the car between front and rear axles, placing the CG of the car where it is supposed to be. This offers great agility and control since there is not much weight on the extremities (which force the car away when cornering). While this is physically the best way of designing a car, this configuration takes all the useable space of the car and this is why it’s only really used for two seater sports cars.
Rear engine + Rear wheel drive
This vehicle architecture helped make Porsche cars famous for their unique driving experience, mounting the engine behind the rear axle, which provides enhanced acceleration. However, since the higher masses of the car are on the rear, the vehicles have a tendency to flick out their back end when cornering. This can make the vehicle rather unpredictable and harder to drive. It is not the best configuration for a race car, but it sure can be fun!