Kawasaki’s Compact Superbike: Ninja ZX-4RR

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Kevin Cameron has been writing about motorcycles for nearly 50 years, first for <em>Cycle magazine</em> and, since 1992, for <em>Cycle World</em>. (Robert Martin/)

Except for one subtle giveaway, this new Kawasaki Ninja ZX-4RR KRT 400cc four looks just like a real superbike. It has twin discs with radial-mount calipers and in general all other visual identifiers of a race-bred sportbike. All I could see at first glance was the slenderness of the chassis upright supporting the right-hand end of its sculpted swingarm. I needn’t have worried: the upright (and the rest of its tubular chassis and its swingarm) are steel, which has three times the stiffness of that traditional sportbike chassis material, aluminum. We praised Honda when in 1987 it equipped its 600 Hurricane with a cost-saving steel chassis. How little we knew—within a few short years 600s became feature-loaded and expensive

As I’ve noted before, when 2008 gobbled up so many people’s disposable income, motorcycle sales crashed. Industry responded with a mechanical variety show as they tested the market with novelties like $13,000 electric scooters. Few takers.

Only when the manufacturers realized that the combo of high insurance premiums and empty pockets hadn’t changed popular taste all that much (people still want the traditional attributes of motorcycles, but are less able to pay $18,000 for them). The recent response has been the offering of highly capable but simplified motorcycles—many of them Twins—at prices people can more easily scratch up. And the trigger word “sportbike” that has sent the insurance industry quivering to its therapists has been carefully avoided.

Superbike Song at a Reduced Cost Means More Buyers

OK, we love the new mid-displacement twins and their new way of delivering performance via flat torque curves, lower weight, and mind-reading responsiveness. But what if we also love the high sweet song of the in-line four? What if sportbikes were our first and forever love? Let’s spec out a bike whose displacement is too small to frighten insurers, and then let’s see how much of the traditional full superbike look we can roll out at a price a lot of riders can pay.

A smaller, 400cc displacement could alleviate some of the insurance pitfalls that supersport and superbike owners experience. (Kawasaki/)

There’s another consideration here. There are already affordable bikes in the 300-400cc displacement slot, so anything that looks like a superbike will have to offer significantly greater performance. Our contemplated product must be “super” at least to that degree.

Although you’ve probably read advance info on this product, here are specs for the 2023 Kawasaki Ninja ZX-4RR KRT: a claimed 414.5-lb. curb weight (dry weight will be less), a short, quick-turning 54.3-in. wheelbase, and with proper sportbike steering geometry of 23.5-degrees rake and 3.8-inch trail. Compression ratio is 12.6-to-1. Coyly leaving out horsepower for the US market, the sheet tells us this 16-valve engine’s peak torque is 26.5 lb.-ft. @ 11,000 rpm, which translates to a horsepower at peak torque rpm of 55.5. If we use arithmetic to find BMEP at this rpm (BMEP is brake mean effective pressure, or stroke-averaged net combustion pressure) we get the quite un-sportbikish number of 164 psi, which is about 15 percent short of a full-boogie sportbike number. BMEP peaks where torque peaks, so if we imagine this engine’s torque to be flat as a board (i.e. the same at peak power as at peak torque), peak power at 13,500 can’t be over 68 hp. But we learned from the European press that claimed power from the Euro-market 400 is 77-78 hp. We’d like to resolve this conflict but for the moment we lack the info to do that.

Horsepower numbers for the US-market 2023 Ninja ZX-4RR have not been released by Kawasaki. (Kawasaki/)

There always has to be more to come next year. By offering this product with enough power to set it apart from the crowd (that word “super”), but not blowing the budget on unnecessary race track features, we pitch it to the largest possible number of buyers.

If this model succeeds in the marketplace, other makers will jump in and step up performance. If a little is good… But as we’ve seen in the dearly departed sportbike past, each year’s amazing up-bump of performance (forged pistons, finger followers, fracture-split titanium rods) came with a price increase. And the businesslike folks in the insurance offices were ready for us (“If you’ll just give me a check now…”).

What Is the Potential Power Output of the Ninja ZX-4RR?

What might such an engine be capable of? At a piston speed we’ve seen many times in the early years of this century, a similar engine filled with premium parts could peak at 17,500 rpm and get oh-so-close to 100 hp. Redline on this model is 16,000 rpm. But let’s not go there. We don’t need to go there, because the used market is filled with that stuff. We want to have a good time on an affordable, insurable bike with a warranty and traditional Superbike good looks.

As I’m sure you have expected, the electronic rider aid features once considered exotic have become mostly just a suburb on a ho-hum computer chip, so that they are now routine: we expect them.

And What About the KOVE 400R?

There are so many descriptions out there of wahoo Chinese-made motorcycles that many are tempted to just say, “When they open a dealership up the street from me and customers start rolling out on new bikes, then I might have a look. But otherwise? Vaporware, junk.”

Possibly not in that category is the Kove 400R, said to be “designed independently by Kove’s engineers.” It is in fact remarkably close in spec to the above new Kawasaki 400. As follows:

Its four cylinders are given bore and stroke of 59 X 36.5mm for a true sportbike bore/stroke ratio of 1.6 rather than the more conservative 1.46 of the Kawasaki. Compression ratio is a modern 13.0:1. Claimed power is 67 hp. @ 13,500 rpm (and a moderate BMEP of 162 psi). Peak torque is given a bit higher in the range than that of the Kaw: it is 26.6 lb.-ft. @ 12,000, which corresponds to almost 61 hp at that point. Weight is quoted as 160 kg (352.6 lb.).

Kawasaki isn’t the only one jumping into the 400cc inline-four game. (Kove Motorcycles/)

Top speed is given as 136 mph, digital fuel injection is by Bosch and steering geometry is given, somewhat unusually, as three numbers rather than the usual two. Rake angle is given at 25 degrees and steering angle is 28. Does this mean that the plane of the fork tubes is not parallel with the steering axis? Maybe. Trail is 3.87 inches.

There are few engine design secrets operating at this moderate performance level so don’t be surprised at the closeness of the numbers. New manufacturers constantly study the work of the established producers—they always have. Once a manufacturer has product lines making money it can afford an R&D department of good capability. That’s exactly what Mr. Honda was up to in the 1950s when he flew away grinning on all his tool-buying trips. He was making sure his engineers had the latest equipment with which they could discover the truth for themselves. Soon they were discovering things that no one else had; Honda took its first FIM world title (the 250) in 1961. There were many more to come.

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