ZX-RR
One hurdle Kawasaki had to overcome in superbike racing was the question of homologation. Race rules required firms to keep certain parts on the racing superbikes to the same spec as on the road bikes. So, if your road bike had steel conrods or CV carburetors, that's what the racebike had to use too. Honda and Yamaha overcame this by making the roadbikes very flash to start with: The Yamaha FZR750R cost nearly $20,000, had titanium conrods and flatslide carbs, and was a super-limited edition (only 500 made in 1989).
Kawasaki took the other path - producing two different models. The basic ZX-7R used a steel tank, dual seat, and CV carbs, while the ZX-7RR had an alloy tank, single seat unit and flatslide carbs more suited to race use.
The 'RR' Ninja has appeared a couple of times since. When Kawasaki gave its ZX-6R a 636cc engine in 2003, it rendered the stock road bike ineligible for 600-class racing. So the firm released a special 599cc version for racing, and dubbed it the ZX-6RR. And when Kawasaki returned to the world of MotoGP racing, its 990cc inline-four racebike certainly deserved the Ninja name alongside its official 'ZX-RR' designation.
The Mini-Ninjas
While Kawasaki has traditionally reserved the Ninja moniker for its premium flagship sportbikes, it's also applied the name to some less awesome machinery.
The Ninja 250 is a great entry-level sportster for novice riders thanks to its 30 HP parallel twin motor and bodywork styled to look like its bigger brothers.
Similarly, the Ninja 500 looked and felt much the same, just with a larger capacity engine.
A Ninja 650 appeared in 2006, and its 650cc twin engine came along with easy handling, a smooth 70 HP and a full fairing. It's no supersport weapon, but as a first 'big' bike it makes a lot of sense for a lot of folks.
One highly sought-after version of the Ninja is the ZXR400. Though rare in America, the little Ninja was popular overseas where strict licensing made it much easier to belong to the Ninja club with a cool looking, great handling "mini-me" version of the ZX-7R.