Harley-Davidson KR
1963 KR at the Art of the Motorcycle Las Vegas
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| Manufacturer | Harley-Davidson |
|---|---|
| Also called | KR750 |
| Production | 1952–1969 |
| Predecessor | WLDR |
| Successor | XR-750 |
| Class | Track racing |
| Engine | 45.26 cu in (741.68 cc) air cooled side valve 4-stroke 45° V-twin, dry sump |
| Bore / stroke | 2.75 in × 3.81 in (69.85 mm × 96.77 mm) |
| Compression ratio | 6:1 or less |
| Top speed | 125 mph (201 km/h) |
| Power | 50–57 hp (37–43 kW) @ 6,000–7,000 rpm |
| Transmission | 4-speed, chain |
| Suspension | Front: Hydraulic fork Rear: swingarm |
| Brakes | none |
| Weight | 320 lb (150 kg) (dry) |
| Related | Model K |
| Successor | XRTT |
|---|---|
| Class | Road racing |
| Engine | 45.26 cu in (741.68 cc) air cooled side valve 4-stroke 45° V-twin, dry sump |
| Bore / stroke | 2.75 in × 3.81 in (70 mm × 97 mm) |
| Compression ratio | 6.3:1 |
| Top speed | 142 mph (229 km/h) |
| Power | 48 hp (36 kW) @ 6,800 rpm |
| Ignition type | Magneto |
| Transmission | Multi-disc dry clutch, 4-speed, chain |
| Frame type | Steel, tubular twin loop |
| Suspension | Front: telescopic fork Rear: swing arm |
| Brakes | Front & rear drum, 50.3 sq in (325 cm2) |
| Tires | Front: 3.00×19 Rear: 3.50×19 |
| Wheelbase | 56.0 in (1,420 mm) |
| Seat height | 30.0 in (760 mm) |
| Weight | 386 lb (175 kg) (wet) |
| Fuel capacity | 6.0 US gal (23 l; 5.0 imp gal) |
The Harley-Davidson KR or KR750 was a 45.26 cu in (741.68 cc) displacement V-twin engine racing motorcycle made by Harley-Davidson from 1952 through 1969 for flat track racing. It was also used in road racing in the KRTT faired version. In spite of technology that was generally obsolete even when the KR was first introduced, it dominated motorcycle racing in the United States due to favorable racing rules. In 1970 it was replaced by the similarly low-tech but long-lived and US race-winning Harley-Davidson XR-750.
American Motorcyclist Association (AMA) Class C racing was created in 1938 in response to low participation in racing and slow motorcycle sales during the decline in consumer disposable income of the Great Depression. The year before, Harley-Davidson was the only factory team to compete. That team had but one rider, Joe Petrali, who had swept every AMA national title in 1935, due in part to lack of competition, as well as his talent. With declining AMA rider membership, the two major factories, Harley-Davidson and , were left with greater influence over the organization, which they used to establish a uniform racing class with a low barrier to entry.
Unlike the many incompatible classes found in car racing, the new class would use the same bikes across many disciplines, including road racing and quarter-mile (short track), half-mile, and one-mile ovals, while leaving out the specialized motorcycles used in hillclimbing, and the large displacement (74 cu in (1,210 cm3) open-class bikes that competed in TT (or TT Steeplechase) racing.
The Class C rules were designed to make racing accessible to the wider public, and not only well-financed professional teams and factories.Homologation rules and bike inspection were used to ensure the amateur riders in the general public could buy the same bikes as the factory team, and buy from the factory's whole catalog of speed parts as well. The displacement formula allowed side valve (or flathead) engines of up to 45.8 cu in (750 cc), but an "equivalency rule" that limited more technically-advanced OHV engines, tantamount to the (primarily UK) import competition, to 500 cc (31 cu in). From the time Class C was established in 1938 until the 1952 KR, Harley-Davidson relied on the 27 hp (20 kW) WLDR, sold with lights, fenders and other equipment, intended to be ridden to the track by amateur racers, prepared by the rider and raced.
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