Kawasaki Z 550F

Kawasaki Z500,Z550 and GPz550

"Announced in 1978, the Z500 was directly related to the Z650. The plain bearing four now had a hyvo cam-chain and six speed gearbox, and displaced 497cc through downsized, 55 x 52.4mm dimensions. In most other respects the whole bike was like the 650, only a bit smaller and lighter. Sitting on a 55 inch wheelbase and wheighing about 430lb ready to ride, it was an inch or two shorter and wheighed 60lb less than big bro.

From the start the 500 had three disc brakes and cast wheels. Styling was best described as "understated", which is a kind of way of saying fairly bland and unadventurous. Still, with 52bhp at 9000rpm it went quite well, in a characteristically revvy Kawasaki way.

BIKE magazines' reporter suggested that the 500 would fill the gap left by the much loved Honda CB400/4, but that didn't happen. It was too expensive for one thing. Part of the little Hondas' secret was a bargain-basement price (less than 900Pds when replaced by the 400T Dream twin in 1978). Making due allowance for inflation, the Z500 really occupied a different sector of the market. If your paying 1,250Pds, why not spend 400Pds more for a Z650, which wouldn't be too financially painful when spread over a three year HP agreement?

A year later, the engine grew another 3mm in the bore to become the Z550 (that's what it said on the side, although elsewhere it was KZ550, because Kawasaki seemed to have adopted the American model designation system). The standard roadster was joined by the LTD, with the expected fat 130/90-16 rear wheel, stepped seat, high handlebars, abbreviated mudguards and suspect handling. 

1981 was the year Kawasaki pulled a rabbit out of their hat, by launching the GPz series of sportbikes. (Incidentally the "z" was supposed to be lower case in the early days, and only started to become a "Z" in 1983, when the GPZ900R arrived on the scene.) Three GPz models were unveiled, having been in development since 1978. At entry level the target for the GPz550 was 120 mph and a 13 second standing quarter-mile. To boost power from 54bhp to 58bhp at 9000rpm, the compression was raised to 10:1 and the cams changed to give 0.7mm more valve lift ans 22 degrees longer duration. In real life the tuned engine gave about 15% more power than the ordinary four.

Tested by the American magazine MOTORCYCLIST, the result was a 12.5 7 second/104mph standing quarter, which seemed incredible. Or completely unbelievable, bearing in mind the claimed horsepower and 200kg weight. British road tests achieved less spectacular results, as usual, but the GPz550 was still substantially faster than the Z550, and effectively offered the same performance as the original Z650.
Nothing had changed on the chassis front. The forks were now air-assisted, a good-in-theory, bad in practice idea, because the legs weren't linked and the volume of air inside was so small that it was difficult to set the pressure at one side, let alone balance the two. "Infinite adjustability", Kawasaki claimed. They weren't joking.

Style was the GPzs' secret of success. Bright red paintwork, subtle graphics, black engine and exhausts, with polished alloy hightlites on the wheel rims and cylinder head. Everybody seemed to like the new look, and it was instantly identifiable, which is a marketing dream."

Classic Japanese Motorcycle Guide by ROD KER