Harley Davidson Silver Art Bar 14 Oz 999 1970 Xr750
An XR-750, number xvi, through the grit at Scioto Downs, Ohio
The Harley-Davidson XR-750 is a racing motorcycle made by Harley-Davidson since 1970, primarily for dirt track racing, only likewise for road racing in the XRTT variant. The XR-750 was designed in response to a 1969 alter in AMA Grand National Championship rules that leveled the playing field for makes other than Harley-Davidson, allowing Japanese and British motorcycles to outperform the previously ascendant Harley-Davidson KR race bicycle.[1] The XR-750 went on to win the most races in the history of American Motorcyclist Association (AMA) racing.[2] [3] [4] [five]
The XR-750 is associated with the careers of racers Marker Brelsford, Cal Rayborn, and Jay Springsteen, and was the favorite motorcycle of stunt performer Evel Knievel.[6] Knievel used the wheel from December 1970 until his last bound in January 1977. An XR-750 was included in the 1998 The Art of the Motorbike exhibition, and one of Knievel's bikes is in the Smithsonian's National Museum of American History America on the Motion showroom.[1] [7]
Rule changes obsolete KR racers [edit]
 At the Barber Vintage Motorsports Museum. | |
| Also called | 70-XR-750 |
|---|---|
| Predecessor | Model KR |
| Class | Dirt track racing |
| Engine | 748 cc (45.6 cu in) air cooled V-twin, 2x 36 mm Mikuni carburetors |
| Diameter / stroke | 76 mm × 81 mm (three.0 in × 3.two in) (1970 iron head) 79 mm × 76 mm (3.1 in × iii.0 in) (alloy caput 1972– ) |
| Top speed | 115 mph (185 km/h)[1] |
| Ability | 82 hp (61 kW) @ vii,700 rpm[1] |
| Manual | Triple chain primary, 4-speed, chain last drive |
| Frame type | Steel twin loop full cradle |
| Intermission | Front: Ceriani telescopic fork Rear: 2x Girling shocks |
| Brakes | Front: none Rear: optional |
| Tires | Spoked wheels, aluminum rims. four in × nineteen in (100 mm × 480 mm) |
| Rake, trail | 26°, 3.44 in (87 mm) |
| Wheelbase | 56.75 in (ane,441 mm) |
| Seat pinnacle | 31 in (790 mm) |
| Weight | 295 lb (134 kg) (claimed) (dry) |
| Fuel capacity | 2.5 US gal (ix.5 l; ii.i imp gal) |
| Oil capacity | 2.75 The states qt (ii,600 ml) |
The AMA Grand National Championship Class C rules, introduced in 1933 and revised in 1954, had an equivalency formula limiting flathead, or sidevalve, engines to 750 cc (46 cu in) displacement, while more modern overhead valve (OHV) engines could be a maximum of only 500 cc (31 cu in).[8] Over time, this displacement reward kept the older flathead engineering science on the rails and discouraged a broader field of competitors. At to the lowest degree 200 homologated examples of a model had to be congenital and made available to the public.[8] The flathead Harley-Davidson KR series had dominated Course C racing, merely by the late 1960s BSA, Norton and Triumph had little market for 500 cc OHV motorcycles, and there was increasing pressure for a single displacement, without reference to valve configuration.[viii] The public was buying 650 cc (40 cu in) and larger deportation British bikes, and they would prove to be competitive, given the chance.[viii]
With the British marques gaining influence in the AMA, in 1969 new rules were established that there would be i maximum displacement for dirt track racing, 750 cc, with no regard for valve type, though the 500/750 OHV/sidevalve split was kept for the fourth dimension being in route racing. OHV engines began to dominate racing, in spite of Mert Lawwill's efforts to delay the inevitable on his flathead Harleys, and the KR bikes were a decade out of engagement and could no longer compete successfully.[eight]
Development [edit]
XR-750 c. 2015: Squad Latus
XR-750 c. 2015: Engine left
XR-750 c. 2015: Engine right
With express time and coin in 1969, Harley-Davidson's racing director Dick O'Brien and his squad used elements of existing designs to put together a new OHV racer, but rather than starting time from scratch they decided to modify their existing OHV racer: the Sportster-based 900 cc (55 cu in) XLR magneto-equipped race engine with a three.0000 in (vii.620 cm) bore and a 3.8125 in (9.684 cm) stroke. It was also large to exist legal, so a modified version was created using the aforementioned basic upper end parts (iron heads and cylinders) merely with a drastically shorter stroke and shorter connecting rods to reduce the displacement to the 750 cc (46 cu in) legal limit.
[viii] These fe head XR-750s of 1970–71 were prone to overheating (humorously called "waffle irons") equally well as having insufficient power. The engine was once again re-designed for 1972 with an all-aluminum head and cylinder package with bigger bore and shorter stroke for the aforementioned 750cc displacement. The frame and the running gear were held over from the KRTT racer, with a Ceriani front fork and 2 Girling rear shocks.[8] The fuel tank, fenders, and rear seat/fender combination were fiberglass, with a snap downward seat cover over a foam cushion.[8] [9] To comply with AMA homologation rules, two hundred examples were made and could exist had upon request at Harley-Davidson dealers, at a price of U.s.a.$3,200, which today with inflation would be about U.s.a.$ 22,329.[nine]
Not unlike other Harley-Davidson engines, the unit construction left and right engine cases split up vertically, and formed four cavities: a middle front end crankcase, a centre rear gearbox, a right side cavity gearcase for the timing train, where the four camshafts are housed, and a left cavity for the 3 row primary drive chain.[8] A row of four camshafts had also been used on the KR racers, inherited from the sidevalve Model WL, and even earlier Model D of 1929.[10] While the single camshaft of other Harley-Davidson designs was cheaper to manufacture, and quieter, four cams allowed meliorate performance, such as greater flexibility in adjusting the cam timing, and the brusk single camshafts are durable, and give the pushrods a straighter path to the rocker artillery.[11]
XRTT route racer [edit]
 | |
| Too chosen | XRTT-750 |
|---|---|
| Predecessor | KRTT |
| Course | Road racing |
| Engine | 748 cc (45.half-dozen cu in) air cooled V-twin, 2x 36 mm Mikuni carburetors |
| Bore / stroke | 79 mm × 76 mm (3.1 in × 3.0 in) |
| Power | Est. 70–100 hp (52–75 kW) (early-late)[ix] |
| Transmission | Triple chain chief, 4-speed, chain final drive |
| Frame type | Steel twin loop full cradle |
| Intermission | Front: Ceriani telescopic fork Rear: 2x Girling shocks |
| Brakes | Front end: 4 leading shoe drum Rear: single disc |
| Tires | Spoked wheels, aluminum rims. Forepart: 3 in × 18 in (76 mm × 457 mm) Rear: 3.v in × 18 in (89 mm × 457 mm) |
| Rake, trail | 24°, 3.63 in (92 mm) |
| Wheelbase | 54 in (1,400 mm) |
| Seat summit | 28 in (710 mm) |
| Weight | 324 lb (147 kg) (claimed) (dry) |
| Fuel chapters | 6 The states gal (23 fifty; 5 imp gal) |
| Oil capacity | 4 US qt (3,785 ml) |
The route racing version of the XR-750 used an aluminum oil tank, had a half dozen U.s. gal (23 l; v imp gal) fiberglass fuel tank, and a fiberglass fairing which included extra rut shielding to protect the rider's left leg when riding in a tuck position.[9] On the top center of the fuel tank was a leather pad with a round cutout for the left-side fuel filler cap.[9] Like the dirt tracker, information technology used a Ceriani fork and Girling shocks, two 36 mm Mikuni carburetors and tuned dual contrary cone exhaust.[ix] Instrumentation consisted of a Smiths tachometer.[9]
Unlike the clay tracker, it came with brakes: a rear disc brake, and in front, a Fontana four leading shoe drum restriction,[9] which is two twin leading drum brakes paired side by side in two drums.[12] The XRTT is the last instance of a competition motorcycle with drum brakes, superseded by disc brakes on all other racing bikes due to the excessive unsprung weight added by the very large drum brake assembly.[9] The official horsepower was never published, simply estimates for the early on 1972 engines were in the high seventy–79 hp (52–59 kW) range, increasing to an estimated 100 hp (75 kW) or more than by 2008.[9]
Racing [edit]
Riders on XR-750s have won 29 of the 37 AMA One thousand National Championships from 1972 to 2008 inclusive.[ii] As well having more wins than whatsoever other bike in AMA racing, information technology has been chosen the "well-nigh successful race bicycle of all fourth dimension",[2] and has a claim to have more wins than any other racing motorcycle in history.[5]
In 1989, Lou Gerencer, Sr. built a hillclimbing XR-750 with an extended swingarm that made the bicycle half once again as long. Adjusted with mechanical fuel injection and nitrous oxide, Gerencer estimated his engine produced over 150 hp (110 kW). The overstressed engine did not last long, but held together long enough to win the AMA hillclimb title.[ix]
Street XR [edit]
Harley-Davidson XR1200 Sportster
As with the KR, customers began asking for a street-legal XR from its debut. Harley-Davidson was dull to capitalize on this need, finally introducing the Sportster XR-chiliad street bike for the 1983 model year, 13 years after the XR-750 racer. The XR-thousand used XR-750 heads, but kept the Sportster engine, frame and other equipment.[ten] Costing about twice the toll of a base model Sportster 40, the XR-1000 sold poorly and many performance enthusiasts but bought an XL and upgraded the heads, carburetors and exhaust themselves at significantly less total cost.[10] The XR-m was discontinued after but two years, and after some other 24 years the Harley-Davidson XR1200 was introduced in 2008 in Europe and 2009 in the US.[13] The XR1200 has less in common with the XR-750 than the XR-1000 did, but has and so far found a warmer reception.[13] [14]
Former Harley-Davidson racing team rider, Mert Lawwill, constructs and markets modified Harley-Davidson XR1200 bikes that are street-legal versions of the Harley-Davidson XR-750 that he raced in the Chiliad National Title.[15] [sixteen]
Jumping [edit]
Evel Knievel began jumping the XR-750 at the meridian of his career between December 1970 and Oct 1976 (although a failed exercise leap was made in January 1977 and captured on flick). Prior to the failed practice bound, Knievel jumped either cars or trucks (or a combination of the two) on the XR-750.[17]
The longest jump Knievel made over cars was 129 feet over 19 cars in 1971 and was featured in the picture show Evel Knievel starring George Hamilton.[18] The longest bound over buses was first attempted with Knievel crashing at Wembley Stadium in 1975 in an attempt to leap 120 anxiety over 13 buses.[19] Five months after, Knievel jumped the XR-750 over 14 buses for his personal record, and globe record for about 25 years,[20] of 133 anxiety at Kings Island.[nineteen]
Knievel set most jump records using the XR-750, merely since 2008, most jump records are held by stunt performer Bubba Blackwell.[21] Currently, the longest jump on the XR-750 by Bubba Blackwell was successfully fabricated in 1999, when he jumped fifteen buses at 157 feet.[xx] On August half dozen, 2015 the daredevil stunt performer Doug Danger[22] at the Sturgis Wheel Rally at the Buffalo Chip, broke Knievel's record for most cars jumped on a XR-750 with 22 cars. Knievel attempted this feat of 22 cars in Monroe, Washington on September 1, 1972 and cleared 21 cars but landed on the prophylactic deck covering the 22nd car. Bubba Blackwell attempted the same 22-car jump In 2001 with horrible consequences. He flipped finish-over-end when he missed the landing, almost died and was in a coma for months. Danger accomplished this feat on Evel Knievel's actual vintage 1972 Harley-Davidson XR-750. With no modification to the bicycle other than relocating foot pegs to conform Doug's height.[23] [24] [25]
Notes [edit]
- ^ a b c d Leffingwell, Randy; Guggenheim Museum Staff (1998), Krens, Thomas; Drutt, Matthew (eds.), The Art of the Motorcycle, Harry N. Abrams, p. 319, ISBN0-8109-6912-2
- ^ a b c Gingerelli, Dain; Everitt, Charles; Michels, James Manning (2011), 365 Motorcycles You Must Ride, MBI Publishing Company, p. 106, ISBN978-0-7603-3474-4,
Most successful race cycle of all time.
- ^ Girdler, Allan; Dewhurst, David (2004), The Harley Davidson Sportster, MotorBooks International, ISBN978-0-7603-1615-3 , retrieved 2011-07-08
- ^ Saunders, Andy (19 March 1996), "Bartels' XLR 1200; Mile racer for the street", Motorcycle.com , retrieved 2011-07-08
- ^ a b "Europe's riders get their own legendary Harley", Bristol Evening Post, Bristol, England, p. 46, xix June 2008,
...the legendary Harley-Davidson XR 750 TM flat track racer - a no-nonsense, purpose-built race cycle that has notched up more wins than whatsoever other racing bike in the history of the sport, this bike does not disappoint.
- ^ Barker, Stuart (2008), "Major Career Statistics", Life of Evel: Evel Knievel, Macmillan, pp. 279–300, ISBN9780312547356
- ^
- "America on the Movement | Evel Knievel jacket and motorcycle". National Museum of American History. 2008-10-24. Retrieved 2009-08-14 .
- Evel Knievel's Harley-Davidson XR-750, National Museum of American History, retrieved 2011-07-10
- ^ a b c d e f g h i Girdler, Allan (1991), Harley-Davidson XR-750, Osceola, Wisconsin: MotorBooks International, pp. 8–16, ISBN0-87938-510-3, OCLC 22812271
- ^ a b c d e f grand h i j k Leffingwell, Randy; Holmstrom, Darwin (2008), The Harley-Davidson Motor Co. annal collection, St. Paul, Minnesota: MotorBooks International, pp. 298–308, ISBN978-0-7603-3184-2
- ^ a b c Norris, Martin (1992), Rolling thunder, Philadelphia, Pennsylvania: Backbone Books, pp. 24–25, ISBNi-56138-131-4
- ^ Buzzelli, Buzz (2006), Harley-Davidson Sportster Performance Handbook (3rd ed.), MotorBooks International, p. 184, ISBN978-0-7603-2353-3
- ^ Martin, Gill (November 1975), "The Brakes of the Game", American Motorcyclist, pp. 10–13, retrieved 2011-07-x
- ^ a b Myles, Paul (31 August 2008), "Motoring Myles: Harley's Got Grip ..At Last", The People – via ProQuest (subscription required) , London, p. 31
- ^ Brown, Stuart F. (6 September 2009), "A Harley lands in America, by fashion of Europe", New York Times, p. AU9, retrieved 2011-07-16
- ^ "Backmarker: Mert Lawwill". motorcycle-the states.com. Retrieved two January 2016.
- ^ Girdler, Allan (2005). Sunday Rider . Retrieved 2 Jan 2016.
- ^ Life of Evel, Stuart Barker, St. Martin'southward Press, 2004
- ^ Los Angeles Times, "Evel Knievel Goes For Broke", February 27, 1971
- ^ a b "Knievel Hurdles fourteen Buses" (Google News), The Montreal Gazette, Associated Press, p. 40, October 27, 1975, retrieved 2011-07-05
- ^ a b "Backwater Bubba Leaps for Leno, Knieve's Marks" (Google news), The Tuscaloosa News, Associated Press, p. 8, February 27, 2000, retrieved 2011-07-05
- ^ "Success!", Golf game Coast Newspaper, Oct 2008
- ^ "Doug Danger — U.s.a.". CycleJumpers.com. Retrieved September 20, 2016.
- ^ Bornhop, Andrew (August seven, 2015). "Doug Danger Breaks Knievel'south Record Daredevil jumps 22 cars at Sturgis, on Evel Knievel'southward 1972 Harley XR750!". Cycle Globe. Retrieved September 20, 2016.
- ^ Panerio, Marry (Baronial 12, 2015). "7 Monumental Moments of the 75th Sturgis Rally". BuffaloCjip.com. Retrieved September 20, 2016.
- ^ "Motorcycle History". Ride Apart. August 3, 2015. Retrieved September 20, 2016.
References [edit]
- "1972 Harley-Davidson XR750; Mark Brelsford's racer", Motorcycle Hall of Fame, American Motorcyclist Association, archived from the original on 2011-07-30
- "1974 Harley-Davidson XR750 Dirt-Tracker; One bike, two champions", Motorbike Hall of Fame, American Motorcyclist Association, archived from the original on 2011-07-30
- Dick O'Brien at the Motorcycle Hall of Fame
- Girdler, Allan (2002), Harley-Davidson Racing, 1934-1986, MotorBooks International, ISBN978-0-7603-1217-9 , retrieved 2011-07-04
Source: https://en.wikipedia.org/wiki/Harley-Davidson_XR-750
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