BMW Motorrad is rumored to be developing a new lightweight frame that will integrate with a three-cylinder engine for an upcoming motorcycle. 

According to Cycle World, the patent application shows a half-frame that directly bolts onto the engine using massive bolts that also connect the cylinder head to the block, resulting in a design that is lighter and more compact than conventional motorcycle chassis.

According to the patent images, the design features a conventional transverse engine, but instead of wrapping an aluminum or steel structure around it, a simple cast-alloy front chassis is attached directly to the engine. This provides a direct connection to the steering head, allowing the swingarm to pivot on the gearbox, with the engine serving as the stressed member. 

The design aims to minimize the bike’s width, a common issue for bikes with transverse-mounted inline engines. It also reduces the parts count and weight, making the design more efficient. BMW’s patent hints at using this new chassis design for a three-cylinder engine, which will further reduce the bike’s width, making it more aerodynamic and less complex than bikes with V-twin or V-4 engines.

BMW has had successful four-cylinder engines like the S 1000 RR, but a three-cylinder engine would be narrower, providing an opportunity for the company to create a narrower bike. BMW has explored the use of three-cylinder engines before, notably in its MotoGP project in the early 2000s. The project yielded a prototype that was later dropped due to technical issues, but it provided the company with the knowledge base needed to develop the S 1000 RR.

Since then, rumors have circulated about a three-cylinder BMW sportbike, with little evidence to support them. However, this patent application, with its specific mention of a three-cylinder engine, provides the first real indication that such a motorcycle is under development.

(source: Cycle World)