Smaller displacement four-cylinder motorcycles were almost extinct, but Kawasaki took a step back and launched a 399cc four-cylinder sport bike. Kawasaki Ninja ZX-4RR is capable of redlining at 16,000 rpm and its 16-valve engine produces 80 horsepower. It is a circuit-focused motorcycle that has a very specific class in its sights.

On the opposite side of the ring, we have our old and trusty Kawasaki Ninja ZX-6R capable of cranking 130 horsepower. ZX-6R is more powerful than Honda’s CBR600RR, Yamaha's YZF-R6, and Suzuki's GSX-R600. The 37cc larger engine of ZX-6R, combined with its ergonomics, chassis, and suspension make it one of the best supersports ever produced.

RELATED: 10 Reasons Why The Kawasaki ZX-6R Is The Best Ninja

10 Why We Love The New Kawasaki Ninja ZX-4RR: A Rare Small Displacement Inline-4

Green 2023 Kawasaki Ninja ZX-4RR KRT on the stand
Lime Green 2023 Kawasaki Ninja ZX-4RR KRT on the stand

It's not often you come across a 4-cylinder engine in a 399cc bike! Don't let the CCs fool you into underestimating the potential of this pocket rocket. The 2023 Kawasaki Ninja ZX-4RR KRT Edition packs a strong punch with its rare inline-4 DOHC 16-valve engine. It has big 57mm forged aluminum pistons with a stroke length of 39.16 mm. All of its cylinders displace around 100cc each to deliver a combined maximum power of 80 horsepower and 35.9 pound feet of torque with a top speed of around 150 mph. It has a 6-speed Transmission and a bidirectional quickshifter.

9 Why The Old ZX-6R Is Better: Trusty 600 Supersport

2022 Kawasaki Ninja ZX-6R on the track
2022 Kawasaki Ninja ZX-6R leaning into a curve on the track

The 636cc long-stroke engine of the Ninja ZX-6R offers riders a significant performance advantage for both everyday use and track racing. With 37cc more engine size than traditional 600cc bikes, it has much stronger low- and mid-range power, making it ideal for street riding and curvy canyons. It produces a massive 130 horsepower, which can be felt throughout the rev range and is especially helpful in making mid-corner power adjustments.

The ZX-6R engine is optimized for performance, allowing improved throttle response and precise throttle control. The DFI technology employs ultra-fine atomizing injectors and precise mapping that enhance the bike's throttle response and reduce emissions. This makes the bike quite lethal machine that can transition seamlessly from canyon carving to the racetrack.

8 Why We Love The New Kawasaki Ninja ZX-4RR: Plethora Of Rider Aids

Kawasaki Ninja ZX-4RR KRT Edition static shot
Kawasaki Ninja ZX-4RR KRT Edition on track, facing right

The ZX-4RR is a track-ready Kawasaki. It has got Kawasaki Traction Control (KTRC) that makes sport riding more fun and keeps rider safe when dealing with low-traction surfaces. This Ninja allows riders to choose from different riding modes, each with a different level of support from Kawasaki electronics. You can get maximum power for sport riding on the track in the first mode, the second option is more suited to normal riding to get a good balance between speed and safety. Rain and slippery roads are always unpredictable, so the third mode helps the rider deal with low-traction situations and restricts the power band. If you are looking for a mayhem mode, you can simply turn the system OFF, or if you love tinkering with electronics, you can also set up your own custom settings.

Related: The Manic Kawasaki Ninja ZX-4RR Just Went Faster Than A Yamaha R7!

7 Why The Old ZX-6R Is Better: Savvy Electronics

2022 Kawasaki ZX-6R Instrument Cluster
Shot of an integrated instrument cluster on the Kawasaki ZX-6R

Kawasaki ZX-6R also comes with the standard Kawasaki Traction Control (KTRC), giving the rider confidence and ability to tackle any road or track. It has three TC modes and two Power Modes, giving you plenty of combinations to choose from to get the most out of your ride. Mode 1 gives maximum power for racetrack performance, while mode 2 is for comfy street performance. Mode 3 - the rain mode - will help eliminate wheel spin and keep the bike straight in the wet. So you still get everything the new ZX-4RR has, just with an old fashion dash, which we happen to prefer.

6 Why We Love The New Kawasaki Ninja ZX-4RR: Chassis Designed By The Kawasaki Racing Team

2023 Kawasaki Ninja ZX-4RR Track
2023 Kawasaki Ninja ZX-4RR sets the racetrack ablaze

The 2023 Kawasaki Ninja ZX-4RR KRT Edition chassis was designed with input from the Kawasaki Racing Team (KRT) World Superbike program. Its trellis frame is made from high-tensile steel, making the frame rigid in the right places, and just the right amount of chassis flex in others. ZX-4RR has inherited key chassis dimensions from its big brother Ninja ZX-10RR, such as engine axis positions, the center of gravity position, the caster angle, and the swingarm pivot position.

5 Why The Old ZX-6R Is Better: Easy Suspension Adjustments

2022 Kawasaki Ninja ZX-6R on the track
2022 Kawasaki Ninja ZX-6R  rounding a curve on the track

The ZX-6R is fitted with the adjustable Showa Separate Function Fork - Big Piston (SFF-BP). It has adjustable spring preload, compression, and rebound damping, with easy access to adjusters at upper fork caps. This suspension can be fully adjusted for racetrack needs and keeps its composure while under hard braking or cornering. At a moment's notice, you can readjust the suspension from racetrack mode to a more comfortable city ride or canyon cruise.

4 Why We Love The New Kawasaki Ninja ZX-4RR: Impressive Stopping Power

Kawasaki Ninja ZX-4RR KRT Edition static shot
Kawasaki Ninja ZX-4RR KRT Edition in green, facing left

To bring the Ninja ZX-4RR KRT Edition to a stop, a pair of 290mm semi-floating front discs and 4-piston radial-mount monobloc calipers are used to provide a firm initial bite and a strong stopping power with control. The rear has a 220mm disc with a single-piston caliper. The Ninja ZX-4RR KRT Edition also features Nissin's latest ABS control unit, which is specifically designed for precise control. To contribute to the ZX-4RR’s lightweight and enhance its handling, star-pattern five-spoke wheels are used that are highly rigid. From the showroom, the bike is fitted with Dunlop Sportmax GPR-300 radial tires.

Related: A Closer Look At Brembo Brakes Used On MotoGP Bikes And What Makes Them Tick

3 Why The Old ZX-6R Is Better: Equally Powerful Brakes

2022 Kawasaki Ninja ZX-6R on the track
2022 Kawasaki Ninja ZX-6R doing a wheelie on the track

The Kawasaki Ninja ZX-6R model also comes with an ABS version powered by Kawasaki Intelligent Anti-lock Brake System (KIBS). On runtime, It analyzes wheel speed, engine RPM, clutch actuation, brake caliper pressure, gear selection, and throttle position to detect how to deal with every situation.

For instance, in a brake lock situation, it temporarily reduces brake-line pressure to help the wheel regain the required traction. Apart from its super hard and controlled braking, the ZX-6R also features little to no brake-lever kickback during ABS activation and employs rear-end lift suppression during hard braking.

2 Why We Love The New Kawasaki Ninja ZX-4RR: Racetrack Suspension

An overhead shot of the 2023 Kawasaki ZX-4RR KRT Edition
The 2023 Kawasaki ZX-4RR KRT Edition seen from above

The ZX-4RR is the first bike in the 400cc class to get an adjustable Showa SFF-BP suspension. It is equipped with 37mm inverted front forks with technology that balances racetrack performance with everyday usability. The large-diameter damping piston in the SFF-BP fork allows oil inside the fork to act on a much larger surface area and damping pressure to be reduced with the same damping force. This design offers a track-ready suspension feel with greater control, stability on the corner entry, and a planted feel when braking. It’s fully adjustable to accommodate a wide range of riding situations.

1 Why The Old ZX-6R Is Better: Better Value

2022 Kawasaki Ninja ZX-6R on the track
2022 Kawasaki Ninja ZX-6R on the straightaway on the track

Both these bikes are great on track and are capable on the street too. They have narrow, lightweight frames and aggressive sportbike riding positions. But the new kid on the block is a very specific tool for a very specific purpose, it is built to dominate the 400cc class on track, as it will quite literally blow anything in that class off the track. It is a fantastic bike, but with a price of very nearly $10,000, it only serves to underline what great value the sub $11,000 ZX-6R offers.