History And Mystery Of The Harley-Davidson XR750

Summary

• The XR750 was Harley-Davidson’s most successful motorcycle built for the race track.
• It has won 28 of the 37 AMA Grand National Championships from 1972 to 2008.
• This was the bike of choice of legendary American stuntman Evel Knievel for his many death-defying jumps and stunts.

If you could count the number of iconic motorcycles Harley-Davidson has produced in the last 120+ years, you would need more fingers and toes. One particular model that thrived on pure adrenaline on racetracks is the legendary XR750. With a rich history in the dirt and mud, it was born in 1970 as an engineering marvel to replace the outgoing KR750 as the new-and-improved race-ready track bike.

For over 50 years, the naturally athletic XR750 would prove itself time and time again as a force to be reckoned with. Powered by a Sportster-based engine, this bike utilized cast-iron heads and cylinders, a magneto instead of a generator, and improved oiling. By 1972, a more powerful all-aluminum alloy engine was introduced to the XR750. With a more powerful drivetrain and nimble nature, this motorcycle would dominate racetracks up until 2008, winning 28 out of 37 AMA Grand National Championships. This earned it the title of “the winningest motorcycle in AMA Pro Racing motorcycle history.” Today, we look back at its glory days.

Brits Inspired AMA To Build Bikes Up To 750cc

Leading up to the development of the XR750, British manufacturers and racers influenced the AMA to feature motorcycles with engines up to 750cc in which both side and overhead valves could take part in the races. In response, the racing and engineering minds at Harley-Davidson felt compelled to come up with a new motorcycle that could be a serious contender on the track against the English. Harley-Davidson Race Team Manager Dick O’Brian and his team helped design the XR750 that would not only go on to replace the KR750, but would also proceed to be one of the highest-performing motorcycles in the world of competitive racing.

The 45 Degree V-Twin Aluminum OHV Engine Was The Beating Heart of the XR750

At the time of its inception, Harley-Davidson’s line of XLRs came equipped with 900cc V-twin engines. In order to meet race spec demands to have the XR750 qualify, Harley’s racing team needed to find a way to tone down the Sportster engine’s power output, and still be the highest-performing motorcycle on the track. After some tinkering with the bore and stroke, engineers were successfully able to dial it back to 750cc.

For a motorcycle meant to be powerful, light, and nimble on the track, Harley-Davidson made the wise decision of developing the XR750’s 45 Degree Aluminum V-Twin engine based on its pre-existing Sportster engine. In 1972, Harley improved upon the XR750 by replacing the cast iron heads with aluminum alloy to be lighter and more heat-resistant, as well as some tinkering with the bores and stroke to pack in a few more horses.

1972 Harley-Davidson XR750 Engine Specs

The XR750 Needed Work Done Before It Could Race

Make no mistake. Just because the XR750 has gone down in history as a successful motorcycle in AMA Pro Racing doesn’t mean it happened overnight. Like any pro athlete, the Harley-Davidson racing team needed to do a lot of research, trial, and error before they were able to engineer the XR750 into racing perfection. The original model utilized cast-iron heads, which proved to be problematic due to their tendency to overheat unless ridden in cooler weather. In addition, should the metal cool down too quickly, the heads could potentially crack. While the original XR750 faired well in short races and cool climates, anything warmer or longer would risk malfunctioning.

By 1972, Harley-Davidson improved upon the XR750’s overheating problem by replacing the cast-iron heads with aluminum. This metal proved itself to be both lighter and more heat-resistant, allowing riders to push the bike harder during longer races without causing further damage. The engine was also placed as far away from the carburetor as possible to help with the bike’s cool-down. By preventing the motorcycle from heating up as quickly as it used to, the XR750 was able to stay at a more stable temperature for longer periods.

Engineers also needed the bike to slim down, too. In addition to the aluminum heads, Harley engineers introduced aluminum spoked wheel rims, a 2.5-gallon fiberglass fuel tank, and a light fiberglass seat. With these modifications, the XR750 completely annihilated the competition. Today, Harley-Davidson continues to be an active contender on the racetrack. But rather than the XR750, the race team pools their energy, time, and resources into their version of a high-performance Road Glide for the popular King of the Baggers race series.

The XR750 Was Popularized by Evel Knievel

Having a reputation for being one of the most unbeatable motorcycles on the racetrack was already a huge boost for the XR750. But when it became the bike of choice for legendary stuntman Evel Knievel, that is when its popularity literally and figuratively took off. He wisely went with the newer version of the XR750 due to it being lighter than the original (a more aerodynamic option when performing his death-defying stunts).

As soon as avid fans saw the motorcycle that Knievel was using to jump everything from multiple cars, Greyhound buses, and Mac trucks, everyone wanted to be like him. So what better way than to get their hands on the same motorcycle that he was riding? Whether they were able to stick the landings as well as him depended on who was attempting the jumps, though.

1972 Harley-Davidson XR750 Specs

50 Years of Excellence

With over five decades of victories under its belt, the Harley-Davidson XR750 secured itself a place in motorcycle history as one of the most legendary bikes to ever hit the track and the streets. After all, a light weight, with a strong race engine built to spec, and a refined cooling system, the XR750 had perfected a recipe for success that proved itself over and over again as a serious contender.

While it was a huge cultural sensation in the U.S., its legend extended to other avid fans across the world as well. Though its production was eventually discontinued in 2013, the XR750 achieved such an iconic status in the motorcycling world that it remains a hit in the used market.

Today’s Successors

Harley-Davidson’s XR750 by itself can be argued to be in a class entirely of its own. One part Sportster, one part race bike, and one part off-roader. It was the perfect culmination of several elements that made it one of the manufacturer’s most successful models in its 120+ year history. Even after 50 years of production, this bike still carries a rich history of excellence. Though no longer in production, parts of the XR750’s DNA can be seen in some of today’s newer models.

Following in its dirt-ridden tire tracks is Harley’s first ADV model, the Pan America. Able to dominate the streets as well as tough terrain, this bike dons the mighty Revolution Max 1250 engine that has enough horsepower and torque to reach 60mph in 3.4 seconds. The same can be said for Harley’s revamped line of Sportsters. The Sportster S follows the XR750’s flat track formula, all while being as light as possible. This makes them the lightest versions of the Sportster class in Harley-Davidson history.

Harley-Davidson XR750 Key Features

• 750cc air-cooled V-Twin engine
• 4-speed transmission
• Won 28 of 37 AMA Grand National Championships
• Lightweight, heat-resistant aluminum heads
• Chain drive