Aerodynamic Innovation in Motocross

Aerodynamics have been making headlines in MotoGP for the last few years, and whether you love the adoption of new technology or despise the appendages sprouting all over the latest generation of racers it’s very clear that honed aero is just as important as a powerful engine or agile chassis in the 2020s. Winglets have already spread to streetbikes, and engineers are inevitably starting to explore whether there’s an advantage to be had from wind-tunnel testing when it comes to off-road competition as well.

We’re not talking about the pursuit of downforce in motocross, at least not yet, but Yamaha has recently filed a patent application in Japan that gives an insight into the sort of work that’s being undertaken in the depths of the R&D department. It shows how future MXers could feature long aerodynamic extensions on the back sides of their forks.

Unlike the very visible aero developments on the latest generation of MotoGP machines, the extended shape of the Yamaha fork isn’t intended to reduce overall drag or to harness the air to create downforce. Instead it’s all about cooling and an opportunity to make bikes smaller, lighter, and less vulnerable to damage, all by tweaking the direction of airflow.

One of the areas where off-road bikes diverge from the norms of streetbike design is in the radiator position. While a streetbike or a supersport racer’s cooling demands are best served by a large unit directly behind the front wheel, mounted relatively low, the same solution would be disastrous off-road. The cooler would be pelted with rocks and clogged with mud in moments. Hence, the normal arrangement is two radiators, one on each side and mounted as high as possible. There’s little point in using a full-width radiator—airflow to the middle would be blocked by the front fender—but the twin radiator setup adds width and weight, particularly as they’re partially obscured by the bike’s fork legs.

As Yamaha’s patent application explains, those fork legs make the flow into the radiators turbulent and inefficient, but the addition of extended sail panels—with a winglike cross section—on the rear edges of the fork legs can solve that problem. The panels, shown to be surprisingly large in the patent drawings, are the width of each fork leg at the front but taper to a sharp edge at the rear, cleanly channeling air into the radiators and simultaneously turning it toward the middle of the bike. That should mean the radiators can be moved closer together, reducing the bike’s width and making them less vulnerable to crash damage, while the efficiency gains should allow the radiators to be made smaller and lighter without any loss of cooling efficiency.

It’s worth noting that while the focus of the Yamaha patent application is firmly on the advantages that the design offers to off-road bikes, the document does include an illustration of a supermoto-style version with a low-mounted front fender. Of course, the design as suggested by Yamaha can only be used on bikes with inverted forks, as the sliding portion of right-way-up suspension would be in exactly the position where the air guides are mounted.