| Revision as of 20:25, 27 January 2016 editDennis Bratland (talk | contribs)Extended confirmed users61,245 edits →Achievements: chron order← Previous edit | Revision as of 09:05, 28 January 2016 edit undoSpacecowboy420 (talk | contribs)Extended confirmed users, Pending changes reviewers5,329 editsNo edit summaryNext edit → | ||
| Line 41: | Line 41: | ||
| The '''Harley-Davidson KR''' or '''KR750''' was a {{Convert|45.26|cuin|cc|abbr=on|2}} ] ] ] ] made by ] from 1952 through 1969 for ] racing. It was also used in ] in the '''KRTT''' ] 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 |
The '''Harley-Davidson KR''' or '''KR750''' was a {{Convert|45.26|cuin|cc|abbr=on|2}} ] ] ] ] made by ] from 1952 through 1969 for ] racing. It was also used in ] in the '''KRTT''' ] 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 ], which went on to win the most races in the history of ] (AMA) racing.. | ||
| ==Development== | ==Development== | ||
Revision as of 09:05, 28 January 2016
Type of motorcycle 1963 KR at the Art of the Motorcycle Las Vegas | |
| 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 |
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 Harley-Davidson XR-750, which went on to win the most races in the history of American Motorcyclist Association (AMA) racing..
Development
Development of the 883 cc (53.9 cu in) Model K street motorcycle began in 1950 in response to increased competition from UK brands Triumph, Norton, and BSA entering the US market in greater numbers due to post-World War II reductions in import duties, and the UK's need to boost exports. Technology found on the European imports, including a hydraulic fork front suspension, a rear swingarm, four-speed transmission, unit construction, and a hand, rather than foot, clutch control, were used on the new K and KR.
Alongside the Model K street bike, the KR racer was developed to compete in American Motorcyclist Association (AMA) Class C competition, which limited side valve (or flathead) engines to 45.8 cu in (750 cc), with an "equivalency rule" that limited more technically-advanced OHV engines, tantamount to the 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. The rules were designed to make racing accessible to the wider public, and not only well-financed professional teams and factories.
Motorcycling writer Kevin Cameron characterized Harley-Davidson as "outside the mainstream of engine development in general, to say nothing of the racing mainstream," noting that, for example, their first use of overhead valves (OHV) on a production motorcycle was one year after the last time a TT race was won by an OHV engine, overhead camshaft (OHC) becoming the only competitive technology in TT racing thereafter. American brands Harley-Davidson and Indian favored flathead engines because riders there rode far longer distances than Europeans, over much rougher roads, with lower octane fuel, and had greater need for low-RPM torque than the greater power offered at higher engine speed of OHV engines. Additionally, while the low-priced Ford Model T car dominated the US motor vehicle market ever since World War I and kept motorcycling in a recreational niche market, in Europe motorcycles were still mainstream, mass-market transportation, with sales and profits that justified ongoing technological investment. That changed after World War II, with lighter, faster, more utilitarian British imports pouring into the US as the UK was desperate for foreign currency to repay war debts, Harley-Davidson and Indian were forced to respond quickly to a newly-competitive and fast-changing market.
Indian chose to meet their competitors on their terms, imitating the OHV parallel-twin design favored by the British imports, but technical hurdles proved too great for the new engine to save the company from its demise by 1953. Harley-Davidson chose to play to their own strengths, creating a pushrod OHV engine that relied on the decades-old side-valve engine's bottom end while advancing more incrementally with new OHV heads and the new, for Harley-Davidson, unit construction, introduced on the 1957 883 cc Sportster.
KRTT road racer
Type of motorcycle| 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 cm) |
| 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) |
Cycle World road tested a 1963 KRTT (or KR-TT) alongside a Harley-Davidson Sprint TT racer. They recorded a top speed of 142 mph (229 km/h), and 0 to 60 mph (0 to 97 km/h) accleration of 5.8 seconds. The 0 to 1⁄4 mi (0.00 to 0.40 km) time was 14.1 seconds at 97 mph (156 km/h).
Achievements
In 1956, every Class C race was won by a Harley-Davidson KR. From 1955 through 1969, 12 of the 15 AMA Daytona 200 national championships were won by KRs. A 1957 KR appeared in the 1999 Guggenheim Museum's The Art of the Motorcycle exhibition in New York and a 1963 KR was in the in Las Vegas show. The AMA Motorcycle Hall of Fame Classic Bikes collection includes two Harley-Davidson KRs: a 1959 KR that is the last motorcycle raced by three-time AMA Grand National Champion Joe Leonard, and Mert Lawwill's 1969 KR750.
Notes
- ^ Gingerelli, Dain; Everitt, Charles; Michels, James Manning (2011), 365 Motorcycles You Must Ride, MBI Publishing Company, p. 99, ISBN 0-7603-3474-9, retrieved May 6, 2012
- Miller, Jim (August 1997), "Unlikely Champion; Quirky, crude, and obsolete from the outset, H-D's KR750 ushered in racing's modern age", Cycle World, pp. 50–54
- ^ Leffingwell, Randy; Guggenheim Museum Staff (1998), Krens, Thomas; Drutt, Matthew (eds.), The Art of the Motorcycle, Harry N. Abrams, p. 247, ISBN 0-8109-6912-2
- ^ Cameron, Kevin (2013), Classic Motorcycle Race Engines: Expert Technical Analysis of the World's Great Power Units, Haynes Publishing UK, pp. 97–99, ISBN 978-1-84425-994-6
- ^ Rafferty, Tod (1997), The Complete Harley-Davidson, Motorbooks International, pp. 52, 76, ISBN 9780760303269
- ^ "Road Tests: Harley-Davidson KR-TT and Sprint CR-TT", Cycle World, pp. 26–31, August 1963
- 1959 Harley-Davidson KR Flat Tracker; Restoring a Hall-of-Famer's ride, American Motorcyclist Association
- Mert Lawwill's 1969 Harley-Davidson KR750, American Motorcyclist Association
| Harley-Davidson model families | ||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Currently produced |
|  | ||||||||||||||||
| Historical |
| |||||||||||||||||
| Racing |
| |||||||||||||||||
| People | ||||||||||||||||||
