Wheels and Tires for Early Electric Vehicles
Version 1.8
Electric vehicles were significantly heavier than other cars of similar body type; they put an extra burden on the wheels and tires. The higher torque of an electric motor at startup put greater stress on the wheel hubs and spokes. To minimize rolling resistance, front wheels were aligned with minimal toe-in (for 1912, Detroit Electric set theirs at 1/4” to 3/8”, from the back of the tires to the front), which made them more susceptible to shimmy.
Wheels
The wooden wheels used for vehicles pulled by animals rotated with minimal friction, and had nearly no torque at the hubs. They were principally designed for vertical support, and lateral loading was not as significant. The same was true for wire wheels designed for bicycles and motorcycles. As the rider leaned into a curve, the weight stayed centered over the tires. Motor vehicle wheels, especially after the advent of powerful brakes on the driveline or at the hubs, needed to have greater torsional strength in both directions of rotation, and more resistance to the lateral loads encountered in fast cornering. Improved versions of these were the wheels of choice until the introduction of the Michelin type of metal disc wheel––patented in 1913, and, in the USA, initially made by the Edward G. Budd Manufacturing Co from 1916 on. Wooden wheels eventually became obsolete, and wire wheels were relegated to sports cars.
Wood
Carriage wheels had thin spokes that were set into mortis joints at the hubs and felloes. A steel-band “tire” around the perimeter of the rim gave it much greater strength and held the spokes tightly in place, since it was added while hot and shrunk into place. A solid rubber tire was often bonded to this steel band. Wheels for carriages were characteristically made slightly dished, with the hub over the inside edge of the rim rather than at the center. This gave better support when cornering, with lateral load shifting to the wheels at the outside of the turn. It also allowed for greater flexing of the spokes, which gave some resilience to road shock. Motorcars used artillery type wheels. Rather than the spokes being set into mortises: the hub ends were wedge shaped, with a tight cluster near the hub, held in place between flanges; providing much greater strength. Second growth hickory (still popular for axe and hammer handles) was the wood of choice for spokes.
Wire
Wire wheels were originally developed for bicycles. They lacked the strength necessary for heavier vehicles. More robust designs, suitable for motor vehicles, were invented by John Pugh and developed in England by Rudge-Whitworth. The ones used on most mid-to-late teens electrics were made by Houk in Buffalo, NY. Following Houk’s death in 1917, the Wire Wheel Corporation of America succeeded them. These wheels used tangentially arrayed spokes, from a much wider hub, to counter torque and lateral cornering forces. They were also dished, bringing the wheel center closer to the steering pivot center, reducing steering backlash.
Wire wheels were 30% to 50% lighter than artillery wheels, and dissipated tire heat better.
S. R. Bailey, who went on to make electric cars of innovative construction, is said to have been the first to put wire wheels on light draft buggies.
Tires
Cushion Tires
Solid rubber tires were well established for carriages and bicycles, especially those running over cobblestones in cities; well before motorcars came around. Rubber tires were made practical by vulcanization. Pure natural rubber had little structural integrity. At moderate temperatures, the weight on a wheel would spread the rubber out like putty; an inner tube would not hold air for long. The latex, would become sticky, collecting pebbles and debris. Charles Goodyear, who discovered the benefits of heating rubber compounds containing sulfur, died in 1860, before the demand for rubber tires. Rubber is elastic due to its long convoluted polymer chains. Vulcanization creates cross-linking, which are bonds between adjacent chains. This makes rubber far more stable. Too much cross- linking (for resilient products) creates hard rubber, used for battery jars (cases), pocket combs, and such. It was better for the purpose than early plastics; Bakelite was too brittle, Celluloid too flammable, and nylon a bit too flexible. Old tires develop more cross-linking, due mostly to the free oxygen in ozone, and can become very brittle. When I drove my 1916 Detroit Cabriolet a few miles to a new storage garage; the remaining 1950s tire (from a fire truck) had become so brittle that pieces chipped off like cold roofing tar.
At first, dependable solid tires were fairly popular on the heavier electric vehicles. Most electric pleasure cars were designed to be driven by their owners. Ladies and gentlemen did not wish to be repairing tires every few hundred miles. Woods, in particular, favored cushion tires, tuning their suspension for them. Although dozens of companies made solid and cushion tires through the early teens, most electrics adopted the Motz Cushion Tire––a good compromise between reliability and shock reduction––as an option. Patented by Charles A. Motz in 1909, and made by the Motz Tire & Rubber Co of Akron, Ohio. They used a special, less vulcanized, rubber formula that had cutouts in the sidewalls to allow more flexibility. Some other, less successful, designs used air pockets, but they weren’t pressurized. After the Palmer/Silvertown pneumatic tire became widely adopted, cushion tires rapidly went out of favor. Many people replaced the wheels designed for the Motz tire with those suitable for the improved pneumatics. Motz tires remained popular for delivery trucks, and Goodyear acquired the company in 1915. Motz tires used rubber without carbon filler. This left them an off-white natural rubber color. Most tires are black because of the addition of carbon black; which adds tensile strength, abrasion resistance, and better heat dissipation.
Pneumatic Tires
Pneumatic tires, which used the highly resilient qualities of pressurized air (predominantly nitrogen), were invented by Robert Thompson, and patented in 1845, for carriages. John Dunlap, who claimed to be unaware of the prior art, re-invented them for bicycles. Thompson’s tires, with a rubberized cloth pneumatic tube, and a leather cover, were fragile, very expensive, and never caught on. Forty-three years later, Dunlap made his tire, at the emergence of the bicycle era. They became quite popular, as most bicycles had no suspension––other than at the saddle––to mitigate road shock. Bicycles were light, so they made modest demands on the natural rubber. Eventually, tire makers started making more heavy-duty tires for light carriages. The Anderson Carriage Co, which went on to make Detroit Electric cars, was one of the first to adopt them.
The Thanksgiving 1895 race in Chicago convinced most participants that pneumatic tires, with better traction and a smother ride, were superior to solid rubber in every way, other than reliability. The resilience reduced rolling resistance, as they could flex to accommodate small stones, whereas steel rims had to lift the entire weight on the wheel over each one.
Tire failure was a significant factor in the commercial demise of electric taxi services in 1901-1902.
Most pneumatic automotive tires made in America from the late 1890s through 1915 were of the canvas fabric type. Rubber can be elastic and resilient, but had limited tensile strength; 5-7 layers of cotton fabric were built up to keep the air pressure from causing them to swell until bursting. These multiple layers became rather stiff, somewhat defeating the nice resilient qualities. Fabric tires had moderately higher rolling resistance. Much of this resistance was produced by friction between the rubberized fabric layers, wasting energy as heat. Heat is an enemy of tires, promoting separation and blistering; leading to structural failure. 1,000 miles was considered to be normal tire life.
To some extent, heavier vehicles needed higher air pressure, to protect the rubber from cutting on impact, when striking a curb or pothole. Higher pressure generally gave lower rolling resistance, due to less sidewall flexing; so electrics ran fabric tires at higher pressure than gasoline or steam cars.
John F. Palmer, an American, originally invented his Palmer Silvertown (a Borough of London) cord “tyres” for bicycles around 1893. The Patent rights were sold to a British company.
B. F. Goodrich merged with the Diamond Rubber Co, which had the American license, and introduced the Palmer cord tire for automobiles in 1913. These used two layers of cotton cords, and advertised 25-30% less rolling resistance than the previous fabric tires. They delivered impressive performance at the 1914 Indianapolis 500, and Palmer/Silvertown tires rapidly became the standard for electrics. After their introduction, other tires, including the Motz cushion tires, virtually disappeared, except for use in trucks.
Firestone introduced balloon tires, with an elliptical profile and improved cord construction, in 1922. They were used on the Detroit Electric model 97 from 1928 on. These required about half the air pressure of earlier tires, giving a noticeably softer ride.