Motorcycle aerodynamics have entered a completely new era in recent years, with MotoGP teams developing increasingly complex and effective solutions to increase speed. But the latest innovation comes from a company that is not involved in the MotoGP world championship, BMW.
While most aerodynamic innovations in motorcycling aim to increase downforce, or at least counteract lift, to push the tires into the asphalt, BMW is taking a different route and trying to use airflow to counteract centrifugal forces, reducing the work the tires have to do and increasing cornering speed.
The Bavarian company has filed a patent application for a ducting system that collects air from one side of the bike and routes it to the opposite side, where it is expelled through jet-shaped outlets. The single image accompanying the patent shows a simplified view of the underside of a motorcycle equipped with the system and demonstrates the path the air takes. The bike in the illustration is moving from right to left, so the widest section of the fairing is facing forward.
You’re probably thinking that the two air ducts and their corresponding jets must surely neutralize each other? The patent explains that, when the bike is traveling in a straight line, this is true: the air on each side of the bike moves at the same speed, so the two ducts cancel each other out. But all that changes when the bike leans into a bend.
This is the clever bit. When you’re making a turn (for example, turning left), the airflow on the opposite side (the right) can separate from the fairing, reducing the pressure on that side. Meanwhile, the pressure on the side closest to the ground (the left in our example) increases. Essentially, it’s as if the road surface and the side of the fairing act together to become a wider and wider channel for the duct on that side, compressing the air towards the intake. As the ducts intersect, this means that the “jet” outlet on the opposite side releases more air, at a higher pressure, pushing the tire to the ground and the bike into the corner.
BMW’s patent goes on to explain that by making the inlet larger than the outlet and giving the outlet a nozzle-like design, it is possible to increase the speed of the air coming out of the “jet”. The document gives the example of an inlet of 5,000 mm2 (7.75 square inches) and an outlet of 1,000-2,000 mm2 (1.55 to 3.1 square inches).
Since BMW doesn’t compete in MotoGP, where an idea like this could be applied to a purely prototype machine, it’s possible that the company is considering using the technology in a road-going sports bike. The M 1000 RR would be the logical machine to adopt it, since it is a circuit-oriented bike that competes in WSBK.