Anticipated for five years as its development was an open secret, the /6 bikes from BMW were better than ever. Whereas a 750cc model, the R75/5, had been the largest-displacement engine, the R90/6 had an air-cooled, overhead-valve horizontally opposed 898cc twin. It had a bore and stroke of 90.0 x 70.6 mm and operated with a 9.0:1 compression ratio. A pair of 32mm Bing constant-velocity carburetors fed the combustion chambers, and output was 60hp at 6,500 rpm. An important and welcome upgrade was the new five-speed transmission.
Weighing in at 460 lb, the R90/6 was fleet enough to run the quarter-mile in 13.45 seconds and could reach 115 mph on a long straight. It was a conservatively handsome bike, with a neatly painted and striped 4.75-gallon tank. The “toaster tank” theme had been abandoned. A larger-capacity tank was available as an option, and because 45 mpg was easily achieved the range of the 1974 BMW R90/6 could exceed 200 miles. The width and comfort of the seat might have allowed the rider to stay aboard that long, too.
The tail section was bare, rather than enclosed as on the flagship R90S, and there was plenty of polished and plated metal. Completing the specifications list, the R90/6 adopted a 260mm front disc brake with single-piston caliper and frame-mounted, cable-actuated master cylinder. At $2,960, it wasn’t at all cheap, but the buyer got a remarkable motorcycle. “The R90/6 is very much at home on the highways and Interstates,” wrote Cycle Guide. “It is smooth, stable, and quiet at touring speeds but some of the concessions to comfort and ride, so valuable in a touring situation, limit it somewhat during hard cornering.”