Material Marvels: The first pneumatic tyres

Materials World magazine
,
25 Mar 2019

Bicycles have been a staple of public transport since the early 1800s, but the invention of pneumatic tyres helped their popularity soar. 

Ever since it first appeared, the pneumatic tyre proved peculiarly attractive to inventors. The impression seems to exist that it is a most imperfect thing, which either requires improving out of existence altogether, or failing that possibility, at least making a great deal better than tyre manufacturers have been able to achieve up to the present,’ said
W Bond in a paper he read at an Institution of the Rubber Industry (IRI) meeting in the UK, in 1930.

As an IRI Fellow, Bond went on to say how between 1850-1930, thousands of patents for bicycle modifications had been submitted, around 15,000 for wheels and 10,000 for tyres. However, few of these produced significant improvements, and none had the level impact brought about by being made pneumatic.

The majority of the patents Bond discussed aimed to prevent punctures or ease their repair, which raised the question about the choice of materials in the then-modern tyres. If getting a puncture was such a common problem, one that would never have happened to old-fashioned tyres, then why was there such a passion for using inflated rubber tubing?

Evolution of the bicycle

Bicycles have provided a liberating mode of transport since they first appeared in 1817, invented in Germany by Karl von Drais, in the form of a gentleman’s push-bike to sit and stride through parks with ease while looking fashionable. It was affectionately called the Dandy horse. Other early designs came with difficulties maintaining decency and comfort while riding, such as the velocipede in 1865 – a wrought iron frame with a springy suspension and the introduction of pedal propulsion.

The two-wheeler was so extremely uncomfortable it was nicknamed the boneshaker and was soon replaced by the ordinary, more commonly known as the penny-farthing, which was an improved experience due to the very large front wheel distancing the rider from the bumps in the road. Change came in the 1880s with John Kemp Starley’s safety bike – named as such because it was safer than falling from a penny-farthing. While the appearance wasn’t set in stone, it generally had more balanced wheel sizes, a diamond frame, better-proportioned handle bar position, and a gear chain mechanism.

‘It shifted their use and public perception from being a dangerous toy for sporting young men to being an everyday transport tool for men and women of all ages,’ said the National Cycle Museum.

‘From the 1890s onward, there have been few fundamental developments of the bicycle. Reductions in component weight, effective braking, multiple gearing and the introduction of sprung suspension have all contributed to the wider acceptance and use of the machine, but the bicycle of the 21st Century has not changed in concept from the machine invented and developed by John Kemp Starley and others in the mid 1880s.‘

While this flurry of innovation targeted the structural aspects of bike design, people still found cycling tough on the backside, and minds turned to the materials used for the tyres.

Dunlop tyres

John Boyd Dunlop – a Scottish veterinary surgeon living in Belfast, Ireland – had a passion for invention and spent a lot of his time working with rubber materials. At that time, the majority of bicycle tyres were wooden wheels protected from damage by strips of iron or steel around the outside. This involved heating the metal sheet in a forge and quenching it over the wheel frame, to get a good fit, and sometimes required rivet studding for traction. In 1839, Charles Goodyear of the USA, discovered vulcanisation of natural rubber and created solid rubber tyres, which were becoming a common replacement for metal. These too were problematic and only partially solved the problem, but Dunlop was inspired and set out to improve the performance of his son’s tricycle.

Dunlop mocked up his first pneumatic rubber tyre in October 1887. He took an inflated tube of sheet rubber, inserted a one-way valve into it and filled the tyre with air until the pressure was high enough to support his son’s weight. Then he tied off the valve to prevent air escaping and fixed the tube around the wooden front wheel of his son’s tricycle, tying it on with a piece of cloth, which he nailed to the wheel frame. 

Though rudimentary, the experiment worked. Dunlop rolled both this cushioned wheel and the bare metal original along his yard, and observed that the air-filled tyre rolled far more easily and for longer. The pressure inside the rubber tube was higher than outside atmospheric air, so it provided resistance that maintained the tyre shape even when holding a person’s weight. This also provided better cushioning for bumps and reduced friction by controlling the size of the contact areas touching the ground at any time. After successive trials, including fixing these tyres to an adult bike, Dunlop was granted a patent for pneumatic tyres in December 1888 and set about making a manufacturing business.

To the mass market

Sadly, this didn’t last and it was soon discovered a pneumatic tyre had been patented by Robert William Thomson in 1846. Thomson’s patent for a rubber tube wrapped in leather had been invented to support horse-drawn carriages and heavy vehicles. Although it categorically came first, it was never actually used to market a product. Nevertheless, the patent office ruled there was too little difference between the methods to mark them apart, and within two years Dunlop’s patent was deemed invalid.

But over those two years, Dunlop’s pneumatic tyres were brought to the public’s attention and popularity gained momentum. Speed cyclist Willie Hume won races in Belfast and Liverpool in 1889, and his pneumatic tyres drew a great deal of attention, crucially from the President of the Irish Cycling Association (ICA) Harvey Du Cros, who approached Dunlop to join the movement. Together, Dunlop and Du Cros went into business and that year established the Pneumatic Tyre and Booth’s Cycle Agency in Belfast to sell to the mass market.

After losing the patent, the team decided to modify the original design, partly for improvements, but also to distinguish their tyres from Thomson’s. They enlisted Charles Kingston Welch to refine it further, and he was responsible for inventing both a removable inner tube and the wheel rim clincher to hold the tyre in place. According to Bond, after the pneumatic tyre itself, these were the next greatest progressions. ‘Probably the first and fundamental change was the separation of the inner tube from the outer cover. That involved new patents altogether, which involved outer cover inextensible edges and a patent by Bartlett which involved an outer cover with hooked and elastic edges,’ Bond said. ‘This was probably the most revolutionary stage in the pneumatic tyre invention.’

Global business

Pneumatic tyres were a hit, and factories were established in Ireland and Scotland, and soon cropped up wherever the cycling manufacturing and rubber supplies demanded. Du Cros was the force behind the success and set up the Dunlop Rubber Company in parallel, in 1889, to manage the rubber supply chain and branch out into other rubber products.

From 1895, Dunlop exited the story, leaving Du Cros sole rights over the tyres and the business. After years of success, the business was sold to a private buyer, before being sold again as a public company. It was renamed, re-sold and exchanged hands multiple times, and today exists as Dunlop, owned by Goodyear Tire and Rubber Company.

Intended for bicycles, the progress made in the engineering of the rubber material, the wheel fittings and the resilience of rubber, made pneumatic tyres ideal for adoption by the automotive industry. As Bond said, ‘The next important basic change seemed to be the invention of cord construction as it was known today [1930], and its use for motor car tyres.   Although it was used for cycle tyres, its adoption for motor tyres was much delayed. A considerable step forward was made when this type of cord fabric was eventually applied to the motor tyre.’

Development of synthetic rubbers in the 1920s hit the business hard, and dramatically reduced the need to source natural rubber, and therefore lowered costs. Instead, a combination of 60%-70% synthetic rubber was required, added to carbon black and various chemicals to process it. Today’s most common tyre material is the synthetic rubber styrene-butadiene.

While Dunlop had cut his ties with the company, his original invention left its mark on the world, with a lasting impact across the sporting, automotive and rubber manufacturing industries, as well as Irish and Scottish heritage. As such, his name is highly recognisable, is still featured on sports equipment, and he was inaugurated into the Automotive Hall of Fame in 2005 for his contribution to transport.

An example of an early Dunlop wheel can be seen in the National Museum of Scotland, donated by the inventor in 1910. The wire-spoked metal wheel has a natural Indian rubber tubing covered in Arbroath sailcloth.