On Pneumatic Tires.

The pneumatic tire…remains a product whose characteristics are not easily predictable or comprehensible by conventional engineering techniques.

- From Mechanics of Pneumatic Tires, published by the U.S. Department of Transportation, 1981. Editor: Samuel K. Clark.

The invention of the wheel is often put forward as a pinnacle of human ingenuity, but it strikes me that the defining characteristic of modern transportation systems is not the wheel but the pneumatic tire. In the United States, vehicles with tires carry twice as much freight as vehicles without them. Tires have an outsized role in individual transportation: The vast majority of Americans commute on tires, outweighing all other modes by about fourteen to one. Tires are on our lawnmowers, those iconic symbols of twentieth-century middle-class independence, and they’re on our e-scooters, perhaps the zenith of twenty-first century globalization and consumerism.

The tire’s meteoric rise might have surprised nineteenth-century observers of the wheel, which took millennia to penetrate (and shape) human culture. Wheels emerged in various forms between 3000 and 4000 BCE. Yet even in spite of its obvious utility, wheeled transportation remained expensive, uncomfortable, and relatively rare well into the early modern period. Richard Bulliet writes that as late as 1570, the number of four-wheeled carriages in Britain “could be counted on one hand,” and even in 1814 there was only one carriage for every 145 British inhabitants. By comparison, today Britain has about one car for every 1.6 people – and roughly half of Brits own or have access to a bicycle.

The popularity of bikes, cars, and wheeled transportation generally has much to do with the tire – and the popularity of the tire owes a lot to bikes and cars. In his 1846 patent, Robert Thomson described his “aerial wheel” – the first pneumatic tire – as an “elastic bearing” mounted to a wheel, “rendering their motion easier and diminishing the noise they make.” He wrote this just two years after Charles Goodyear received the patent for his rubber vulcanization process; rubber was, at long last, finally good for making stuff, and Thomson had a prescient understanding of how vulcanized rubber could make wheeled transportation more efficient and comfortable. By far the dominant mode of wheeled transportation of the time was horse-drawn carriages, and Thomson ran a series of tests to understand how a carriage with pneumatic tires would fare. He described in detail how pneumatic tires made travel dramatically more comfortable for passengers, and reduced the total drag on the vehicle by as much as 68%. In time the benefits attributed to tires would multiply: They enable much higher speeds of travel; they improve traction dramatically; they allow a vehicle to maintain traction even when the road surface is uneven; they can greatly reduce the sound of the wheel rolling over the ground.

But Thomson was too early, and his carriage tires had virtually no impact on the course of history: As Henry C. Pearson noted in 1905, “they do not appear to have come into use except as a curiosity.” Thomson himself also seems to have turned his attention to other things; he later moved to Java and invented an improved fountain pen. An incredible technological breakthrough had occurred, but nobody wanted to put pneumatic tires on their carriages.

Forty years passed, with pneumatic tires nowhere to be seen. Solid rubber tires gained some popularity for farm vehicles; Thomson himself patented a solid rubber tire in 1867, six years before he died. But the big thing that changed around that time was the fact that humans began pushing themselves around on wheels – instead of being dragged in carriages by horses.

Velocipedes – known as “boneshakers” in the US – were a significant step towards the modern bicycle, incorporating not just two wheels but also a crankset and pedals, which allowed the rider to apply force directly to the front wheel instead of pushing off the ground like a scooter. One French manufacturer alone produced two hundred velocipedes a day in 1869 – a higher production rate than any auto manufacturer would reach for the next forty years. Heavy, crude, and wildly popular, velocipedes would serve as the impetus for a number of technological advancements, from radial ball bearings to improved road surfaces to, in 1888, the reinvention of the pneumatic tire by John Boyd Dunlop.

Dunlop – a veterinarian who took a wildly successful shot at improving his ten-year-old son’s tricycle – saw what Thomson had before him: Wheeled vehicles slow down when they go over bumps, and the smoother their ride is, the more efficient they are. When wheels roll up the front of a bump they transfer a little kinetic energy into gravitational potential energy; when they roll down the back side of the bump some – but not all – of that transfer is reversed. The most efficient wheeled vehicles travel on the smoothest possible surfaces (train tracks) on the roundest possible wheels (railroad wheelsets); their motion can be described almost as a straight line, and they lose very little energy to being jostled around. But bikes, cars, and e-scooters must deal with much more varied surfaces, and every time they bounce up and down, a little bit of their kinetic energy is dissipated as heat. A bumpy road surface vibrates the bike and its rider, and that vibration causes everything – the tires, the structure of the bike, and the muscles and skeleton of its rider – to literally warm up.

It warms my heart to think of Dunlop – forty-eight years old, with a horse-shoeing business that employed a dozen people – springing to action to help his kid’s trike go faster. As a 1981 Dunlop-sponsored book summarizes, “the boy’s report on the performance of the new machine on its new tyres was most encouraging.” At this point vulcanization was a mature technology, and the bicycle industry was big enough for Dunlop to imagine a sizable market for his invention. He promptly filed a patent (it was later invalidated) and within a year was supplying crude pneumatic tires to bicycle racers in Belfast.

In 2014, I visited a Taiwanese tire factory as part of a bicycle sourcing trip. At the time I had a fairly good handle on the manufacturing processes required to build bike frames, but the sounds, smells, and overall texture of tire manufacturing all felt foreign. Tires – whether for bicycles, automobiles, or any other purpose – are made via basically the same methods that Dunlop used in 1888, by building up raw rubber on a fabric casing and a pair of wire beads and then vulcanizing the entire assembly. The tire industry has dominated global rubber production basically since its inception; today it consumes roughly three quarters of global natural rubber production, and similarly large portions of synthetic rubber. Pneumatic tires are the killer application for vulcanized rubber. They allow us the flexibility to travel over all sorts of surfaces, from asphalt and concrete down to gravel, dirt, and sand. Pneumatic tires allow our transportation infrastructure to be flexible, reliable, and comfortable, and enable us to travel to places that we are either unable or unwilling to get to via rail, ship, or air.

It’s difficult for me to conceive of a world without pneumatic tires. They enable a lot of the things I enjoy in life. Then again, tires are part of a specific technological ecosystem; just as they were impractical before the bicycle, it stands to reason that they might be impractical at some point in the future.

SCOPE CREEP.

• Scope of Work’s workshop scavenger hunt kits are back in stock! Get yours 🔜 here.
• This issue relied heavily on The History of the Pneumatic Tyre, 1981, by Eric Tompkins, and Rubber Tires and All About Them, 1906, by Henry C. Pearson. For much more on rubber, check out our (growing!) collection of feature articles on the subject. I also referenced my copy of Bicycling Science, in which David Gordon Wilson explains the forces that affect modern bicycle performance. Appropriately, his explanation focuses on aerodynamics, and it sometimes feels as if he introduces other factors mostly to explain how small they are in comparison. Wind resistance dominates the power-speed relationship on modern bicycles, and the biggest factor in wind resistance is the frontal area of the cyclist and the bicycle they ride. The weight of the bicycle, the quality of its bearings, and the size and mechanical properties of its tires are all surprisingly insignificant. If you, dear reader, want to go faster on your bike, the most effective way of doing so will almost certainly be to reduce your frontal area. But getting into an aerodynamically efficient position can be fatiguing, and over the past decade or so, more and more cyclists have used supple tires as a way to reduce rolling resistance and increase comfort. Sure enough, David Gordon Wilson does note that the reduced drag that comes from installing low-loss tires “comes at perhaps the least degree of pain” of any of his other recommendations.
• The shift from internal combustion engines to electric vehicles will be a good step for atmospheric CO2, but it’s possible that EVs will produce higher levels of PM2.5 emissions – which, as this 2022 study in Los Angeles showed, are increasingly driven by brake wear and tire wear.
• Moquette is a durable pile fabric, often made from wool, which is used to upholster the seats and floors of commuter rail cars. Moquette is used prominently in the London Underground, and the London Transport Museum has a ton of information about the textile and its history on their website.
• Snecked masonry is a type of stonework in which roughly rectangular stones of mixed sizes and proportions are arranged to form an irregular pattern.
• A few weeks ago, a federal appeals court held that when a privately-developed standard (like ones for highway bridges, motor vehicle turn signals, and bike helmets) is adopted into public law, it can then be disseminated freely without risk of violating its copyright. ‘“In a nation governed by the rule of law, private parties have no business controlling who can read, share, and speak the rules to which we are all subject,” EFF Legal Director Corynne McSherry said. “We are pleased that the Court of Appeals upheld what other U.S. courts, including the Supreme Court, have said for almost 200 years: No one should control access to the law.”’
• If you’re in the market for a half-hour TV show that is hilarious and sincere and totally surprising, my highest recommendation goes to Reservation Dogs, which just finished its three-season run on FX/Hulu.

Thanks as always to Scope of Work’s Members and Supporters for making this newsletter possible. Thanks also to Paul and Ziggy for sending links.

Love, Spencer

p.s. - I’ll be back with more on rubber in the coming weeks ;)
p.p.s. - We care about inclusivity. Here’s what we’re doing about it.