2023 Kawasaki Ninja ZX

The junior four-cylinder, the Kawasaki Ninja ZX-4RR, is back in the hands of the company that made it famous.

Photography by Ryan Nitzen, Kevin Wing

You guys in America missed out because the 1990s were a golden era for little sports bikes:

Honda’s CBR250RR and CBR400, Yamaha’s FZR250 and 400, Suzuki’s GSX250 and GSX-R400, and of course, the Kawasaki ZXR400.

In my home ground of Australia, these things were ripping roads and ear drums apart in the ’90s, riders bouncing the little four-pots towards, in some cases, near 20,000 rpm redlines. As a sport bike-mad teen, all I wanted was a Honda CBR250RR (junior riders were limited to 250cc or less while they were classified as learners). I got a Yamaha SRV250 café racer, which wasn’t love at first sight but grew into love over time.

That was over 25 years ago, more than half my lifetime, but I can still remember those little screamers and lament that they have all but disappeared from the world’s roads.

But they haven’t disappeared entirely.

Kawasaki made noise a couple of years ago that they intended to build a 21st-century four-cylinder 400, and, what’s more, Kawasaki USA intended to homologate it and bring it to America. Typically, we are the last to get pretty much every cool model from the major manufacturers, but this time, we’ve jumped the queue to the front, and here it is. A bike teenage me would have done very questionable things to have it in my garage.

The 2023 Kawasaki ZX-4RR is a complete anomaly in modern sport biking. It’s especially confusing because Kawasaki has a firm hold on the junior sport bike market with their Ninja 400, which has sold more than enough across the globe to sink a couple of the container ships on which they left Japan.

The 4RR is all-new, but you could be forgiven for thinking the spec sheet reads something like the larger ZX-636. Items like ram air, fully adjustable suspension, four-piston monobloc brakes, quickshifter, and a screaming 16,000 rpm redline is normally reserved for race-spec 600s, but all of it can be found on the 4RR for under $10K at $9699 for this KRT Edition (there’s an extra base model for other markets that’s not coming to America).

The 4RR feels like it’s a Ninja 400 that’s spent too much time eating burgers and not enough time running, a bit like the guy writing this article. The chassis is a Ninja 400-style steel trellis number that runs the Horizontal Back-link and BFRC-lite shock directly off the swingarm, so you get an exceptional feel from the back end despite the settings being on the soft side straight out of the box.

The ride position is a near-perfect mix of sport bike and naked bike, with the clip-on handlebars mounted above the top triple-clamp. For a 6’1” tall rider like me, you can sit almost bolt upright on the freeways but still get behind the screen when you need to at your favorite backroad.

Because you’re only dealing with a claimed 414 pounds of curb weight, the little 4RR is exceptionally nimble. Running the 37mm inverted Big Piston Separate Function Inverted Fork, you can haul the 400 through corners with the kind of mid-corner speed 1000cc bikes could only dream of. It’s so light on its feet and such fun to exploit, but if you need to change settings, that’s simple enough as it’s fully adjustable with all the adjustment screws for compression and rebound damping and preload located at the top of the fork.

Although the Ninja 400 has a larger, conventionally mounted 41mm fork, the ZX-4RR’s greater piston size of the inverted Showa 41mm fork allows for less damping pressure compared to the regular cartridge fork of the 400 but with the same damping force. This, in turn, gives a smoother initial fork action at the top of the stroke and, thus, greater pitch control when the front brake lever is applied and the weight is transferred to the front tire.

The chassis provides a silky-smooth ride that handles rough potholed roads surprisingly well, but the real star of the game is that engine.

Like a teenager listening to Rage Against the Machine, the energy this little engine exudes is boundless. With 16,000 rpm to play with, you owe it to yourself to hold gears a while longer and just let the little 400 scream its lungs out between turns.

I know this fun can only last so long, so there’s got to be some performance on offer, which there is. As expected, there’s not a lot below 6000 rpm, but the internals are so light that it’ll rip past this marker way quicker than a 600. Get the engine spinning north of 9000 rpm, and that’s where the fun is.

You’ve got roughly 60 horsepower on tap in standard form (stick on a slip-on exhaust, and you’ll easily crack 70 horsepower at the wheel). There’re three riding modes, Sport, Road and Rain, and a manual Rider mode that allows you to program one of two power modes (Full and Low), plus the traction control level (1-3 plus Off) and the Kawasaki Quick Shift System (KQS) at your disposal. This is an excellent amount of tech for such a low-capacity machine, although given the price is just under $10K, you’d expect it so.

But with 60 horsepower on tap, I doubt many people will ride in anything other than Full power mode, as Low makes the 400 feel like a 250. You can be pretty rough with the ZX-4RR—rip back through the six-speed gearbox at high rpm, and the slipper clutch takes care of most of the rear wheel chatter (it can’t get rid of all of it)—it’s a very well-rounded package that almost any rider of any skill level will enjoy.

Although it was quick, I absolutely loved my time on the ZX-4RR. Hopefully, I’ll get a spin on the race bike that Chuck Graves is building, and that I’m sure will start populating various club race grids around the country soon—although my big hope is Kawasaki puts together a one-make MotoAmerica series for these bikes. Imagine 25 of these charging into turn one at Road Atlanta!

Given the price and the fact Kawasaki’s own Ninja 400 KRT is priced at almost half the MSRP at $5899, I don’t think Kawasaki has totally cannibalized its own market with the ZX-4RR, and I’m sure, side by side, these bikes can live harmoniously. But, if I had the coin, I know where I’d be heading, if only to hear the scream of that four-cylinder at 15,000 rpm.

Our location for the track test of the 2023 Kawasaki ZX-4RR was Thunderhill in Northern California. And it was the longer three-mile east track, so there was plenty of time to turn the screws on this little 400.

At 6’1” and 180 pounds, I felt immediately comfortable on the ZX-4RR. The bike did not have an overly aggressive riding position—the stock handlebar, seat, and foot position were comfy, and I didn’t feel like I was on a small bike.

The slim tank led to good control and helped the rider in the tucked position. Kawasaki utilized feedback directly from their KRT efforts in WorldSBK to construct the chassis, and the result was an outstanding balance that helped keep the bike planted.

Starting up the ZX-4RR for the first time, it has that sweet Kawasaki whirring sound that would be familiar to anyone who’s ridden a ZX-10R in the last 10 years.

The all-new 4.3-inch TFT color dash is easy to navigate through the bar controls where you can select between the three pre-set riding modes of Sport, Road of Rain, plus one of two power modes of Full or Low, to help manage throttle response, and you also have three traction control modes, plus that up and down quickshifter.

Heading out to the track for the first time, the base setting for the suspension felt good. I didn’t change any settings in either my first or second session, although this can easily be done as both ends are fully adjustable.

Getting on the throttle, you hear something a bit different coming from the engine. It almost sounds like a mini F1 car! The throttle response is strong, and you hear that sound of the inline four-cylinder screamer engine. Picking up the pace and getting into faster turns seven and eight, you hear the engine come to life. It rides very smoothly and likes to be in the higher revs. The 10-14,000 rpm mark is the sweet spot, but it took a few laps to find the right gears to utilize the power delivery.

Helping to control and smooth the gear change is a slipper clutch to help stop the rear tire from hopping or skidding into corners, which can be dangerous if you’re not comfortable with it, not to mention tiring.

The front brakes on the ZX-4RR feature a pair of 290mm semi-floating front discs mated to four-piston monobloc calipers; Kawasaki claims the dual caliper setup makes for smoother braking and is worth the extra weight.

It’s an exceptionally easy bike to get used to. The power delivery is smooth and usable, and the chassis gives loads of feedback. Finding the sweet spot with the quickshifter and throttle combination took a few sessions to get down, but once it was understood, the bike was so easy to manage through the gears. Only once did we get the rear end to step out after five sessions, but after a few tweaks of tire pressure and rear suspension settings, we were good to go again.

About 10 of us were on track at one time, and I swear I could hear the giggling and laughing at how much fun we were having on these little Kawasakis. If you are an experienced track rider/racer, there’s very little you need to do to make this an extremely fun machine. Likewise, if you’re a new rider looking to improve your skills and want room to grow as you gain speed and confidence, this is also an excellent option. CN