This summer, at least 50 million American families will climb into their vehicles and speed off on road trips. The U.S. has long been the world’s pre-eminent car culture, so it’s easy to forget that the amenities which make those long trips possible—smoothly paved highways, cheap motels or campgrounds, roadside cafes and gas stations—haven’t always been a part of the American landscape.

Before the invention of automobiles, the average American rarely traveled more than 12 miles from home, because that was how far a horse and wagon could comfortably go in a day. Henry Ford introduced his inexpensive Model T in 1908, making car ownership possible for people of average means. But at first, drivers still weren’t able to expand their range very much, because the infrastructure wasn’t there: 90% of American roads were what people called “wish to God,” as in drivers wished to God they could drive on pavement rather than stones, ruts and mud.

Things had to change, and they did. By the mid-1920s, the term “autocamper”—describing drivers whose trips were long enough to necessitate stops at night to camp—entered the national lexicon. Thanks were due in large part to Henry Ford and three of his friends: the inventor Thomas Edison, the tire-company magnate Harvey Firestone and the naturalist and author John Burroughs. There is no record showing which of the quartet came up with their catchy nickname, but from 1914 through 1924 “the Vagabonds” undertook highly publicized summer car trips around the U.S. In the process, they encouraged multitudes of their countrymen to fill up their gas tanks, pack a tent and canned food, and try it themselves.

At the time, true national celebrities were rare; radio and movies were still primitive and television had yet to be imagined. But Ford and his best friend Edison qualified as American icons, having blessed the public with wonders never previously imagined. Edison invented the phonograph, bringing music into homes, and perfected the incandescent bulb, which lighted up houses far better than candles and smoky oil lamps. In addition to the Model T, in 1915 Ford also introduced the $5 workday for his employees, essentially doubling their salaries and pressuring rival manufacturers to do the same. Between them, Ford and Edison raised middle- and working-class Americans to new heights of prosperity and leisure.

So when Ford and Edison, joined by Firestone (one of Ford’s major suppliers) and Burroughs (Ford enjoyed his books and essays on nature), set out on their summer car trips, Americans were eager to share every moment. The Vagabonds’ car-and-truck caravan was routinely followed by packs of journalists and film crews, the latter often hired by Ford. In theaters, feature films were proceeded by news “shorts,” and audiences enjoyed watching Ford perform basic roadside repairs and Edison snooze beside a campfire—moments just as scripted for public consumption as the on-screen histrionics of Rudolph Valentino and Clara Bow.

At every stop, the famous travelers granted interviews to local press, emphasizing that they were simply pals out for the same kind of carefree fun that anyone with a car and a sense of adventure could enjoy. Edison swore that the Vagabonds picked each day’s route by whim: “We steer by the sun and compass only.” The inventor also claimed that the men didn’t shave—“not a razor in the party”—and that their dinner frequently included fresh fish they caught themselves, “with a bent pin hook and a birch limb rod.”

In fact, the four celebrities weren’t exactly roughing it. The Vagabonds traveled with staff who put up spacious tents, prepared gourmet meals from ingredients carted along in a refrigerated truck and provided the supposedly rough-and-tumble adventurers with freshly-ironed clothes each morning. The Vagabonds themselves lounged comfortably in spacious Packards and Lincolns, sometimes driven by uniformed chauffeurs, while their employees rattled along in Model Ts.

Ford, who had on-and-off plans to run for president on the simple platform of going to Washington, D.C. and “throwing a wrench in it,” used some interviews with the press to espouse controversial opinions about war, labor unions and the sleaziness of Wall Street, and racist theories about the international intrigues of Jews. Edison was constantly quizzed by the press about new and amazing inventions, though by this time he no longer had any to tout. But it didn’t matter: The Vagabonds had attained folk hero status, and their fans emulated them with their own summer car trips.

By 1920, with an estimated half of America’s 10 million car owners now classified as at least occasional autocampers, a few towns opened municipal auto camps, offering free overnight space for drivers on their way somewhere else. The hope that these visitors on wheels might buy meals or gas from local merchants was fulfilled beyond expectations.

Two years later there were as many as 6,000 auto camps, some of them massive like Overland Park in Denver, which had space for 2,000 cars and tents. For the first time, gas stations opened along widely used roads, and new state taxes on gas financed road upgrades. Cafes sprang up on stretches of highway between towns, so it became progressively easier to purchase meals rather than to lug along canned goods and build cooking fires. Rand McNally published its first national road maps in 1924, and many cities established speed limits—anywhere from eight to 12 miles an hour was the average. (Police hid behind bushes or billboards and used stopwatches to time passing cars.)

Inevitably, the Vagabonds found themselves overtaken by the cultural trend they had popularized. So many Americans took to the road in summer that the car trips of four men, even famous ones, were no longer unique enough to attract press and film coverage. After Burroughs died, following their 1920 excursion in New York state, Ford, Edison and Firestone tried carrying on by including presidents: In 1921 Warren G. Harding joined them in camp, and 1924 found the Vagabonds calling on Calvin Coolidge at his summer home in Vermont. But in both instances, the president rather than the Vagabonds commanded the resulting headlines.

In his 1926 memoir, Firestone wrote that he and his two friends gave up their trips after 1924 when the pressure of constant coverage made it impossible for them to relax and have fun. In fact, the opposite was true. Americans were still awed by Henry Ford and Thomas Edison, but the summer road trips that they cared about now were their own.

—Mr. Guinn is the author of “The Vagabonds: The Story of Henry Ford and Thomas Edison’s Ten-Year Road Trip,” which will be published by Simon & Schuster on July 9.