IJMS / Ed Youngblood / The Birth of the Dirt Bike

The Birth of the Dirt Bike: Technology and the Shift in Attitude toward American Motorcyclists in the 1970s

Ed Youngblood

Prior to 1960 it was practically impossible to buy a purpose-built off-road motorcycle[1] in America. People enjoyed racing and riding off the road, but up through the 1940s they had to make do with big Indians and Harley-Davidsons that were built for street and highway use. These motorcycles were not designed to carry their riders through mud, water, and rough terrain. They were heavy and had short, soft suspension with little ground clearance, and tended to get hung up on every root or rock they came upon. By the 1950s, so-called “lightweights” began to arrive from Great Britain, but “lightweight” was still a relative term. These motorcycles—brands such as Triumph, BSA, Matchless, Norton, and Ariel—were lighter and had better ground clearance than their American counterparts, but they were still heavy and designed primarily for use on the road. And they often had unreliable electrical systems that failed under wet and dirty riding conditions. As in America, off-road motorcycling in England and Europe during this era was conducted with modified street machines.

Under these circumstances, the motorcyclists who wanted to experience the joy of racing and off-road riding simply made do. They removed as much weight as possible by removing extraneous parts, tried to seal vital electrical components from dirt and moisture, and did whatever they could to make their air induction systems less susceptible to water. Competition was fair and vigorous because everyone was equally handicapped by the same primitive equipment, but the state of technology and design significantly limited the number of people who could ride off the road. One needed to have engineering and mechanical skills to make the necessary changes to the motorcycle, and it helped to be a huge brute of a guy to muscle a heavy road machine over a scrambles track or through the woods.

But big changes were in store for off-road motorcycling during the decade following World War II, thanks to the advent of new materials and the emergence of new technology. Some of the conditions that set the cultural stage for an American dirt bike revolution included post-war prosperity, greater mobility, international influence, and a new optimism toward America and its future.

Not only were many Americans looking for adventure by the 1950s, but they were adopting novel international tastes. Returning soldiers had just spent several years in Europe and the South Pacific, exposed to different people and ideas, and many became curious about the wider world. GIs were exposed to a new kind of motorcycling in England and Europe. The bikes were more agile, quicker, lighter and better handling than their Harley-Davidsons and Indians. Many wanted to own such bikes, and a revolutionary economic policy called the Marshall Plan provided them the opportunity.

British motorcycles were scarce prior to World War II, but this changed rapidly with the passage of the Economic Cooperation Act of 1948, empowering the Marshall Plan for European economic reconstruction. Reversing Smoot-Hawley[2] isolationism, the Marshall Plan encouraged international trade and the exchange of technology. Hence, British motorcycles were imported and sold in America during the 1950s, largely because they were inexpensive, exciting, maneuverable, available, and different. As European industries were reconstructed, NSUs, BMWs, Ducatis, Parillas, Moto Guzzis and other marques arrived from the Continent. Finally, a third wave occurred in the 1960s, introducing us to Honda, Yamaha, Kawasaki, Suzuki, Hodaka, Bridgestone, and many more.[3] More people could buy bikes because more motorcycles were available. This influx of new and relatively inexpensive product was caused—directly or indirectly—by the Marshall Plan.

Finally, another post-war development probably influenced motorcycle purchases more than any other: the age of optimism. America had whipped its enemies in a just war, the economy was improving, and Americans were becoming excited about their potential to live better lives. They were convinced about their scientific and industrial superiority. What better way to celebrate this optimism than to buy a new motorcycle, especially one of the exotic foreign jobs that made one feel sophisticated.

The changes that resulted in the modern dirt bike also required leaps forward in technology, largely a result of wartime technical development and the scientific stimulus inherent in the post-war Marshall Plan.

Significant pre-war developments in metallurgy were accelerated when government resources were pumped into the development of lighter, faster, more maneuverable, and more durable military aircraft. Lightweight alloys were developed and new welding techniques were invented. In pre-war motorcycles, many critical parts of the frame, such as steering heads and suspension mountings, are heavy cast-iron lugs into which thick-walled, mild steel frame tubes are brazed or sweated. These frames were heavy, labor-intensive and relatively expensive to manufacture.

Furthermore, dimensional adjustments could not be made without reshaping the complex cast iron lugs. With the advent of lightweight, low carbon content chromium alloys and new tube-to-tube argon gas welding techniques, motorcycle designers could dispense with heavy cast iron parts and weld up frames composed entirely of light-weight, thin-wall tubing, creating lighter, more durable, and more affordable motorcycles.

The need to create lighter and more durable equipment for the military resulted in molding and material forming techniques that brought new miracle products, such as Nylon (invented in 1934) and polystyrene (1937) into commercial use. One could now achieve complex and sophisticated shapes for non-metallic, water-proof air boxes, fenders, and other motorcycle parts that helped get a rider through wet and nasty off-road conditions. Moldable plastics also made the solid state ignition possible, vastly improving electrical reliability.

But the greatest technological development was a breakthrough in two-stroke engine performance from the German Democratic Republic (DDR) in the late 1950s. Walter Kaaden, a young German engineer, worked for the motorcycle company MZ.[4] The DDR wanted MZ to demonstrate East German superiority on the Grand Prix road racing circuit. Kaaden focused on the simple and easy-to-manufacture two-stroke engine.

Kaaden pioneered many of the principles of modern two-stroke design, including disc valves, timed porting, and combustion chamber “squish design.” At one point he experimented with a kind of piston-driven supercharging to force more fuel and air mixture into the combustion chamber. It produced more power, but not enough to be competitive, and the result was a fragile, short-lived engine. Those who witnessed these compressor-induction MZs on the race track recall they were the most shrill and outlandishly noisy engines ever heard. Kaaden, who knew that noise represented wasted energy, realized he needed to do more than just force more fuel and air through an inefficient combustion chamber. Kaaden knew he needed to keep the fuel charge in the combustion chamber a little longer, and by studying harmonics, he hit upon the principle of the expansion chamber. Not only did he perfect the idea, but he reduced it to mathematics. By controlling the angle of diverging and converging cones, and the length of the main exhaust chamber and the “stinger” at the end of the pipe, Kaaden learned how to actually make sound waves compress the fuel charge or scavenge the fuel charge at the precise moments he wanted either to happen. This, along with more sophisticated cylinder porting, resulted in a major breakthrough. By 1960 Walter Kaaden’s little two-strokes had suddenly leaped ahead of the overhead cam four strokes in power-to-weight ratio, and he had a potential world beater on the Grand Prix circuit. The power of his racing engines was increased by 25 percent between the 1960 and the 1961 racing seasons (Henshaw).

When Kaaden’s secret found its way into the commercial market,[5] the final technological component was in place for a revolution in the design of off-road motorcycles. Not only was it a lighter and less costly vehicle, but all of these technologies came together to create a significantly smaller and more maneuverable package, affordable to more young people, women included.

Economic and technological developments are only two parts of the three-part formula to engender historic change. Third is the human factor, creative and visionary individuals dissatisfied with the status quo, who can find ways to use technology and the social climate to realize their ideas. Two who stand out are John Penton and Edison Dye. From the day in 1948 when John Penton buried his big Harley axle-deep in the soft Michigan sand at the Jack Pine Enduro, he decided there had to be a better way to build an off-road motorcycle. His life became a quest to realize that vision, and he applied all the technical elements described above—lightweight plastics, chrome molybdenum tubing, and a two-stroke engine—to create the Penton motorcycle.[6]

In America, several lightweight, purpose-built off-road motorcycles preceded the Penton, among them the British Greeves and DOT (1953), the Czech CZ (1954), and the West German Maico (1955). All were unsuitable for road riding, and were systematically marketed strictly for racing and off-road use. Penton wanted a motorcycle suitable for younger people and adults, available in quantity, and that would take dirt bikes to a new, higher standard of performance and reliability. During its ten-year run in the American market, the Penton motorcycle achieved these goals. Approximately 70,000 off-road motorcycles were manufactured at the KTM factory in Austria during the decade, bearing the Penton brand in the United States and the KTM label in European markets. The Penton motorcycle excelled at both motocross and enduro competition, and became the model for a flood of off-road motorcycles that poured out of Japan’s large-production factories in the 1970s.[7]

John Penton understood that his product would benefit from an altered image. Like Honda’s Kihachiro Kawashima, Penton strategically chose to avoid the word “motorcycle” when promoting his product.[8] He wanted an image associated with athleticism and wholesome activity, and he marketed his products as “sport cycles,” a term that KTM still uses today (Youngblood, John Penton).

Edison Dye made his mark on off-road riding by importing not just a superior motorcycle in the Swedish Husqvarna, but by importing with it a whole new motorcycling culture (Youngblood, “Godfather”). When Dye hired world champion Torsten Hallman to show Americans how to ride motocross in 1966, then followed it up with a coast-to-coast road show of European champions in 1967 and subsequent years through his Inter-Am Motocross Series, racing in America was changed forever. American competitors and fans developed a wild enthusiasm for motocross that resulted in a thirteen-year domination of world class competition a generation later.[9] Then John Penton took what was fundamentally a motocross machine and outfitted it with enduro equipment, giving Husky and the two-stroke motor its first AMA Enduro Grand National Championship in 1969 and setting off seventeen years of domination for Husqvarna in the American championship enduro series.[10]

Dye understood that the Husky had a strong Swedish cultural identity and mystique, and Hallman had proven that no one could sell a Husky like a Swedish motocross star. Dye knew he had to market not just a motorcycle, but a lifestyle. The image presented by Hallman elevated physical fitness, discipline, diet, and training. To reinforce and link these lifestyle qualities with the Husqvarna brand, Dye circulated news releases claiming that Swedish researchers had determined that motocross riders were some of the most physically fit athletes on earth, and published in 1968 a book about fitness and training, written by Swedish motocross world champion, Rolf Tibblin.

Motocross and the lightweight two-stroke motorcycle entirely changed the nature and image of motorcycle competition in America, and the evidence is in the numbers. The traditional form of American motorcycle competition was flat track racing, conducted on quarter, half, and mile dirt oval tracks. In 1965, the American Motorcyclist Association sanctioned 156 flat track races and only 15 motocross races.[11] Over the next decade, the AMA’s program of sanctioned events exploded, and by 1975, the AMA’s calendar of sanctioned flat track races had grown to 660, but sanctioned motocross events skyrocketed to more than 1,500.[12] Flat track increased five-fold during the decade, but motocross increased a hundred-fold!

Not only was it cheap and easy to buy a competitive racing bike at any dealership, but motocross tracks were easier to build and maintain than dirt ovals; thus event promoters were quickly attracted to motocross. From the late 1970s until the end of the ’80s, motorcycle sales declined precipitously, owing to a poor domestic economy, environmental issues, and increasing prices for Japanese imports. By 1985, the AMA’s calendar had settled back to about 1,100 sanctioned motocross events, but flat track had slipped almost back to 1965 levels, with only 191 sanctioned events.[13] The situation has not significantly improved for flat track racing, despite the fact that motorcycle sales began to rebound again in the early 1990s. In 1995 the AMA’s calendar of sanctioned motocross had grown to just under 1,300 events while only 140 flat track races were sanctioned nationwide.[14]

With the emergence of motocross there came a change in the image of motorcycle racing in America. Traditional flat track racing had developed a rough-and-tumble carnival image, in fact because many of the races were promoted at carnivals and county fairs during the 1950s. Flat track racers were seen as a hard-living group, making their money in a dangerous profession, traveling long hours from race to race, sleeping in their trucks, eating at greasy spoons, and smoking cigarettes. Motocross, on the other hand, brought an Olympic mystique, complete with international rivalries and riders with personal trainers.

Bruce Brown did not design, build, or import motorcycles. He made a movie, and when On Any Sunday hit mainstream theaters in 1971, Americans were given a new perspective on the world of off-road motorcycling. With narration by co-producer Steve McQueen, the film set new standards in live action photography, presenting motorcycle racing as a varied and physically demanding sport. Unlike the low-budget, drive-in biker flick quickies, On Any Sunday required two years to shoot, and over 150 hours of footage was distilled into the 90-minute final product. An original musical score by Dominic Frontiere reinforced Brown’s message that motorcyclists are good people: fun loving, harmless, happy, and sometimes heroic. On Any Sunday sent countless families running to motorcycle dealerships to outfit themselves for the joys of dirt biking. It romanticized a wholesome image of motorcycling, made its racing champions look like great gladiators, and depicted off-road riding as a bond that brings families together.

American Honda, the Grey Advertising agency, and the “Nicest People” advertising campaign have been widely credited for orchestrating a sea change in the way Americans thought about motorcycling. The credit is deserved, but the technique of selling a lightweight two-wheeled product by distancing it from the traditional concept of motorcycling in America was continued by Penton, Dye, Brown, and others.

The purpose-built dirt bike created a market Japanese manufacturers were ideally positioned to exploit. Japanese post-war reconstruction became an opportunity to establish a higher standard manufacturing quality. Japan also decided to gamble on world domination a second time, but this time in the commercial market place. Thus its factories were designed for high levels of production which European and American factories of the period could not match.[15] Japan began to fill the huge On Any Sunday pipeline with product sufficient to put hundreds of thousands of Americans on affordable, reliable dirt bikes.

Japanese production in large quantities greatly expanded the entire American motorcycle market. For example, in 1955 the entire U.S. motorcycle market represented annual sales of approximately 36,000 units. By 1970 motorcycle sales had ballooned to over 1 million units, 165,000 of which were dirt bikes. In other words, sales of dirt bikes alone in 1970 were four times greater than the entire U.S. motorcycle market in 1955.^[16] Furthermore, the Japanese products achieved a level of trouble-free performance inconceivable to motorcycle designers a decade earlier, and this reputation of high reliability brought a new segment of customers to motorcycling.

The serial production dirt bike contributed to a lasting change in world-wide motorcycle design and manufacturing. It launched product specialization and niche marketing in the motorcycle industry, resulting in products as diverse as the large and luxurious Honda Gold Wing, and the lean and lithe Gas Gas trials bike.^[17] Today one can buy a bike designed precisely for a specific use, and quality is superb. However, product specialization has resulted in segmentation of the motorcycling community into ever narrower interests, perpetuating the idea of motorcyclists as a “minority community,” despite the great increase in motorcycle sales.

Just about the time Walter Kaaden’s advanced two-stroke technology was becoming adopted by the worldwide motorcycle industry (1962), Rachael Carson was publishing Silent Spring, a bellwether warning of technology out of control that helped launch a popular environmentalist movement in America. The two were breakthroughs in scientific thinking whose paths would cross in a cultural collision exactly a decade later. Consequently, the American off-road motorcycle revolution possessed a shadow side that would darken an otherwise improving image.

Dirt bikes became so popular that they were practically ubiquitous. In the early days they were manufactured with unmuffled expansion chambers and were conspicuously noisy. By 1972 it was estimated that more than five million off-road vehicles (motorcycles, dune buggies, snowmobiles, all-terrain vehicles, and four-wheel-drives) were in use on public lands, and most were off-road motorcycles. Complaints against the expanding use of off-road vehicles caused President Nixon to issue on February 2, 1972, Executive Order 11644, calling for the regulation of motor vehicles on public lands.^[18] EO 11644 signaled the official declaration of a war for public lands that continues to the present day. Federal regulators saw the Order as a practically unfulfillable obligation to provide for appropriate and regulated use of off-road vehicles, motorcyclists saw it as an effort to unfairly limit their enjoyment and eventually shut them out entirely, and some environmentalist organizations saw it as entirely unwarranted, preferring rather to see all public lands closed to motorized use.

Although federal agencies responding to EO 11644 have strived to objectify the problem and reduce it to statistical and scientific components, the real battle has continued on an emotional level. Ironically, On Any Sunday gave the opponents of off-road motorcycles their most enduring weapon. Depicting the mass start of the legendary Barstow to Vegas cross-country desert race from the bird’s eye vantage of a helicopter, narrator Steve McQueen asserted facetiously that the event raised “a dust cloud that settled three weeks later over London.” Environmentalists found the image and the assertion neither facetious nor funny. Thus, the movie that helped popularize off-road motorcycling became a weapon against it. Although point-to-point desert racing was not characteristic of how most off-road motorcycles were used, the horrendous image of the start of the Barstow to Vegas race became a symbol of the destruction of which every small trail bike was thought to be capable.

The battle over public lands raised America’s motorcycling community to a higher level of responsibility than ever before, largely through the work of the American Motorcyclist Association. The AMA put significant funding into researching and publicizing scientific techniques for the responsible management of public lands, added professionally trained staff to raise the dialogue with environmental organizations and federal land managers, encouraged its local clubs to model conscientious and responsible motorcycle use, and became the first motor sport governing body in the world to mandate mufflers on full racing machines, hoping the example would be emulated by individual road and off-road motorcycle owners. For a while the Motorcycle Industry Council worked in step with the AMA, but recently has reduced funding for land-use programs commensurate with the decline of off-road motorcycle sales, and currently will not oppose excessive motorcycle noise for fear of offending its after market members.^[19]

While motorcycles have been used for off-road riding since the early twentieth century, not until after World War II were specialized off-road motorcycles designed and mass produced. This change in product development resulted from new materials and technologies dating from the late 1950s and early 1960s. The advent of the purpose-built off-road motorcycle contributed significantly to the boom in American motorcycle sales. The relative small size, light weight, and ease of handling of the typical off-road motorcycle facilitated the expansion of the motorcycle market to both genders and wider age groups. Marketing leaders of the era—including Edison Dye, John Penton, and Bruce Brown—positioned the lightweight off-road motorcycle as a healthy, sporting product for people of all ages, and thereby penetrated a larger middle class market.

The off-road motorcycle helped alter and broaden the image of motorcycling toward athletic, wholesome family activity. However, government and the environmental reaction to the proliferation of off-road motorcycles brought a new set of problems. Both the American Motorcyclist Association and the Motorcycle Industry Council adjusted their missions, altered their operations, and expanded their budgets to deal with the issues raised by the regulation of vehicles on public lands brought about in the 1970s by Executive Order 11644. While the advent of the off-road motorcycle improved the image of the sport in many ways, on balance it did not eliminate negative attitudes, but rather shifted to new areas the problematic image of motorcycling in America.

1 The terms “dirt bike” and “off-road motorcycle,” as used below, refer to motorcycles either purpose-built or modified for recreational use over natural terrain. The terms apply to motorcycles used for organized endurance competition, casual trail riding, and many forms of racing.

²Also known as the Hawley-Smoot Tariff Act, this legislation, signed in June 1930, brought the U.S. tariff to the highest protective level in history. The act brought retaliatory tariff acts from foreign countries, U.S. foreign trade suffered a sharp decline, and the depression intensified.

³ The Marshall Plan was designed for European economic recovery, but the Japanese subsequently benefited from the nearly tariff-free trading environment created and proven effective by the Plan. The destruction and subsequent rebuilding of industries caused by the war in Europe and Japan left America’s antiquated motorcycle industry at a distinct disadvantage. Old production techniques and aging factories eventually took Harley-Davidson to the brink of bankruptcy, and some historians believe that one of the factors that took Indian into bankruptcy in 1954 was the fact that the impoverished and cash-strapped company overextended itself to build an entirely new factory for the purpose of competing with British and Continental imports. Furthermore, when Harley-Davidson introduced its first lightweight two-stroke motorcycle, it used an engine appropriated from the German firm DKW, and when Harley-Davidson undertook to affix its marque to a full line of lightweight motorcycles, it acquired the Italian Aermacchi factory (1957) rather than try to develop and build new designs in the United States.

⁴ MZ arose from the ashes of the old German transportation firm DKW, which had a large factory in Zschopau. Production resumed there in May, 1950, under the new marque MZ. Walter Kaaden, who had worked on V1 and V2 missile development during the war, became MZ’s chief engineer, turning his attention to two-stroke engine design and development. For a comprehensive history of the MZ firm, refer to Henshaw.

⁵ When Walter Kaaden’s little two-stroke MZ suddenly burst into prominence on the Grand Prix road racing circuit in 1960, it was widely believed that his team was capable of snatching a championship from the big four-stroke multis during the 1961 racing season. But Kaaden’s rider, Ernst Degner, had a different idea. Degner developed an elaborate plan to defect, and did so at the Swedish Grand Prix in 1961, while leading the world championship series, thus dashing any hopes of bringing the championship back to MZ and East Germany. An account of these events can be found in Hazelton. Furthermore, Degner departed with Kaaden’s designs and mathematical formulas for the expansion chamber. That knowledge quickly went to Japan, where a national strategy to enter the world consumer market with inexpensive motorcycles was already underway. A simple, inexpensive two-stroke with a vastly improved power-to-weight ratio may have contributed more than any other single factor to the success of the Japanese motorcycle industry. How thoroughly the two-stroke engine influenced off-road motorcycling is demonstrated by the fact that prior to 1969 when John Penton won the AMA Enduro Grand National Championship, no two stroke had ever carried a rider to the overall title. But only once following 1969 has a two-stroke failed to win the Enduro Grand National Championship. Incidentally, Ernst Degner earned a world championship in 1962, riding a Suzuki, which was the first two-stroke motorcycle to win such a title.

⁶ After first approaching and being rejected by Husqvarna, John Penton took his concepts to the KTM firm in Austria. KTM was a manufacturer of bicycles and mopeds that had been in and out of motorcycle manufacturing on a relatively limited scale since the second World War. The collaboration between Penton and KTM not only produced ground-breaking off-road motorcycle designs, but moved KTM into a position of strength that has enabled it to continue to compete against the Japanese.

⁷ John Penton’s sons Jack and Tom, and his nephew Dane Leimbach, all of whom were his protégés and highly-skilled off-road competitors, served as consultants to Japanese manufacturers for the development of off-road motorcycles following the sell-off of the Penton brand to KTM in 1975.

⁸ In The Pursuit of Dreams: The First 50 Years of Honda, Kihachiro Kawashima recalls, “At that time, motorcycles were seen as part of a lifestyle, inhabited by leather-jacketed gangs who were rowdy and anti-social. . . it was necessary that the image of motorcycles and motorcycling should be changed, so that society would accept the motorcycle as an economical and convenient form of transportation.” Penton also subscribed to this idea, except his goal was to sell motorcycling not as convenient transportation, but as healthy recreation.

9 Beginning in 1981, the American team won the Motocross des Nations—the team world championship of motocross—for 13 consecutive years, then again in 1996 and 2000 (FIM).

¹⁰ The Penton brand disappeared when its American distributorship was purchased by the Austrian firm KTM in 1977. The Husqvarna marque was acquired by Cagiva and is still manufactured in Italy. Information about the original Penton and Husqvarna motorcycles can be found at .

¹¹ American Motorcycling, January through December, 1965.

¹² AMA News, January through December, 1975.

¹³ American Motorcyclist, January through December, 1985.

¹⁴ American Motorcyclist, January through December, 1995.

¹⁵ Ironically, it was American J. Edward Deming who taught the Japanese the quality control techniques that later became known as Total Quality Management (TQM). Deming, whose methods were based on statistical process control techniques pioneered at Bell Labs, was invited by the Japanese Union of Scientists to come to Japan in 1947 to consult on the rebuilding of Japanese industry. His advice had been largely ignored in America. Harley-Davidson did not adopt TQM manufacturing techniques until 1985.

¹⁶ These numbers are estimates provided by DJB/Associates LLC, a leading market consultant to the motorcycle industry. No documented sales and import figures exist for the 1950s, and the Motorcycle Industry Council did not begin to systematically collect and document U.S. motorcycle import and sales figures until early in the 1970s. In the absence of systematically collected sales figures from the period, data from DJB/Associates is considered soundly derived and the best available.

¹⁷ To appreciate the diversity that is now encompassed by the term “motorcycle,” consider the fact that the total weight of the Gas Gas observed trials motorcycle is approximately 150 pounds, while the six-cylinder engine alone in the luxurious Honda Gold Wing touring motorcycle weighs 280 pounds, nearly twice the weight of the complete Gas Gas, chassis, wheels, and all!

¹⁸AMA News, March 1972, 27.

19 The American Motorcyclist Association has campaigned against excessive motorcycle noise since the 1950s. In the early 1970s the Motorcycle Industry Council funded an extensive public information advertising campaign around the slogan, “Less Sound Equals More Ground,” and its Japanese manufacturer members created a land-use fund based on annual unit sales of off-road motorcycles, providing funding on an equal basis to both the MIC and the AMA. Today the AMA continues to campaign against excessive motorcycle noise, using the slogans “Noise Annoys,” and “Loud Pipes Risk Rights,” and the Association’s promotion of responsible off-road motorcycle use continues to the present day, as witnessed by the February 2002 American Motorcyclist, which contained no fewer than five articles on the subject.

Henshaw, Peter. The Encyclopedia of the Motorcycle. Edison, NJ: Chartwell Books, 2000.

Hazelton Publishing Ltd., et. al., Motocourse: 50 Years of Moto Grand Prix. Surrey: Hazelton Publishing, 1999.

The Pursuit of Dreams: The First 50 Years of Honda. Tokyo: Nigensha Publishing, 1998.

Youngblood, Ed. “The Godfather of Motocross.” Racer X Illustrated (June/July 2000).

---. John Penton and the Off-Road Motorcycle Revolution. North Conway, NH: Whitehorse Press, 2000.