The motorcycle rumor making the rounds this week is that Kawasaki is working on a Ninja ZX-4R, a 400cc four-cylinder sportbike based on the ZX-25R currently offered in Asian markets.

The ZX-25R was revealed almost a year and a half ago, though like all things, it certainly feels longer thanks to the pandemic. The quarter-liter Ninja was created for markets like Indonesia and Japan, where insurance and licensing class structures create a demand for 250cc sportbikes. With most bikes in the class powered by Singles and Twins, the four-cylinder ZX-25R immediately stands out.

In other markets, however, the ZX-25R made little sense as it would be seen as being two small, and likely too expensive for its size. A 400cc version, however, would be a better fit, and could be sold at a price point that would meet market expectations. That’s what makes this week’s rumor of a ZX-4R version of the ZX-25R so appealing.

Like most rumors involving the Big Four, this one seems to have started with Young Machine, a Japanese publication known for its renderings of motorcycles that have not been officially revealed. YM’s post was speculative in nature, discussing the possibility of a ZX-4R and how that could be achieved. What it didn’t claim was any inside knowledge that confirms a ZX-4R was in development. That hasn’t stopped a number of publications from running with the story, turning speculation into rumor without a shred of proof.

Well, we’ve got that proof, in the form of a Kawasaki patent that confirms that the company has been working on a ZX-4R. The focus of the patent is a fairing design with an integrated duct to redirect air around the radiator and header pipes and directly to the engine itself.

The first illustration in the patent isn’t what you’d consider “detailed”, but you can see the general shape of the bodywork compared to the photo of the ZX-25R above.

The drawings in the patent depict a motorcycle that resembles the ZX-25R, and we can see the patent’s concepts at work with the side ducts in the sportbike’s fairing. According to the patent, this additional air cooling is needed because of the high-revving nature of the engine. The ZX-25R in particular has a high redline of 17,000 rpm, so the ducts would help provide more cooling without having to enlarge the radiator.

Subsequent diagrams in the patent are more detailed and show a clear relationship to the ZX-25R.

While the link between the patent and the ZX-25R is apparent, it’s the text that directly links it to a ZX-4R, saying “the present invention can be more preferably applied to a vehicle having four-cylinder 400 cc engine.” There is no mention at a 250cc version in the patent, so this tells us that the ZX-25R’s fairing was originally designed with a 400cc model in mind but adapted to the 250cc model. This kind of flips the narrative around, so instead of the ZX-4R being derived from the ZX-25R, it’s actually the other way around.

It remains to be seen whether Kawasaki will proceed with a ZX-4R, or if it will stay with a ZX-25R for Asian markets. The larger model would be a better fit for European and North American markets, but there would have to be a business case for it to potentially replace the Ninja 400.

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