For 30 years, Kawasaki’s ZX-6R has ruled with its racetrack DNA—a 636cc inline-four born to scream at redline. Aprilia’s RS660, which stormed onto the scene in 2021, answers with a street-tuned parallel twin and tech-savvy agility. I’ve seen how their philosophies collide: raw power versus accessible innovation. I’ve cut through the specs and marketing fluff to check which bike truly rules the asphalt.
High-Rev Screamer vs. Torquey Twin
The Kawasaki ZX-6R packs a 636cc inline-four engine—a configuration beloved for its ear-splitting wail and explosive top-end power. For 2025, Kawasaki tweaked the camshafts and intake to boost low-to-midrange grunt, making it friendlier for city riding.
But let’s be real: this engine still lives for the redline. With 127 hp at 13,000 rpm, it’s a thrill to attack a canyon road, but around town, you’ll need to downshift constantly to stay in the powerband. One rider said, “The ZX-6R doesn’t wake up until you’re above 8,000 rpm—it’s like riding a coiled spring.”
Compared to the Aprilia RS660 and its 659cc parallel-twin. This engine is all about accessibility. With a 270-degree crank that mimics a V-twin’s punchy character, it serves up 105 hp and a flat torque curve peaking at 49.4 lb-ft by 8,500 rpm.
You get an instant throttle response without revving the guts out of it. Merging onto highways or blasting out of corners feels effortless, and the engine’s burbly exhaust note adds to the streetwise charm. “The RS660 pulls like a freight train from 4,000 rpm,” noted a test rider. For stoplight-to-stoplight riding, the Aprilia’s torque advantage is undeniable.
Verdict: The ZX-6R dominates if you crave top-end screams. The RS660 wins for usable, everyday power.
Precision vs. Practicality
Sportbikes need to carve corners, but street riders also demand stability and comfort.
The ZX-6R uses a Showa SFF-BP inverted fork and Uni-Trak rear suspension, both fully adjustable. On smooth roads, it’s razor-sharp—lean angles are limitless, and feedback through the bars is telepathic. But push it onto bumpy urban streets, and the stiff setup can feel punishing. “After an hour on rough pavement, my wrists and back were begging for mercy,” admitted one commuter.
The RS660 counters with a KYB inverted fork (adjustable for preload/rebound) and a monoshock rear. While firmer than a standard naked bike, it’s noticeably more compliant than the Kawasaki.
The Aprilia’s shorter wheelbase and lighter 403 lb curb weight (vs. the ZX-6R’s 436 lbs) make it feel flickable in traffic yet stable at highway speeds. Opt for the RS660 Factory model, and you’ll get Öhlins suspension for even smoother damping. “It’s the Goldilocks of sportbikes—agile but not twitchy,” praised a reviewer.
Verdict: The ZX-6R shines on pristine pavement; the RS660 balances agility with street-friendly comfort.
Race-Ready vs. Rider-Friendly
Sportbike ergonomics often sacrifice comfort for performance. But how much can you tolerate?
The ZX-6R’s posture is pure supersport: low clip-ons, high rear set pegs, and a committed lean. It’s fantastic for dragging knees but brutal in traffic. “My hips felt like they’d aged 20 years after a 90-minute ride,” joked a rider. That said, seasoned sportbike fans might find it manageable—the seat is slightly roomier than older 600cc rivals.
The RS660 takes a smarter approach. Its clip-ons sit higher, the seat is plusher, and the footpegs are lower. You sit in the bike, not on it, reducing strain on your wrists and back. Add standard cruise control—a rarity in this class—and the Aprilia becomes a legit touring companion. “I did a 200-mile day and stepped off feeling fresh,” raved an owner.
Verdict: The RS660 is the clear choice for daily comfort. The ZX-6R? Save it for short, spirited rides.
Tech & Safety
Modern riders expect electronics to enhance both fun and safety. Here, Aprilia flexes hard.
The ZX-6R offers KTRC traction control, power modes, and an optional quick shifter. Its new 4.3-inch TFT display with smartphone connectivity is slick, but the lack of an IMU (Inertial Measurement Unit) means no cornering ABS or wheelie control. “It’s competent but feels a generation behind,” shared a Kawasaki owner.
The RS660’s Aprilia Performance Ride Control (APRC) suite is a masterclass. Standard features include:
- Cornering ABS (with a 6-axis IMU)
- Bidirectional quick shifter
- Wheelie control
- Engine brake adjustment
- Cruise control
- Launch control
It’s like having a MotoGP engineer tweak your ride. “The electronics make you feel invincible, even in the rain,” said a test rider.
Verdict: The RS660’s tech package is unbeatable for street safety and versatility.
Where Does Your Money Go?
The ZX-6R starts at $11,399 (non−ABS) or $12,399 (ABS). The RS660 begins at $11,749, undercutting the Kawasaki’s ABS model. For that price, you get more advanced electronics, better components (like Brembo brakes), and Italian flair.
However, Kawasaki’s reputation for bulletproof reliability could save money in the long term, whereas early RS660 models had occasional issues.
Verdict: The RS660 offers more bang for your buck upfront, but the ZX-6R might cost less over time.
Which Bike Owns the Street?
If you’re a track-day regular who occasionally commutes, the Kawasaki ZX-6R delivers raw speed and razor-sharp handling. But for 90% of street riders, the Aprilia RS660 is the smarter pick. Its torquey engine, comfy ergonomics, and space-age tech make it a joy in real-world conditions—no compromises required.
