The Reason Why Tires Are Black
The additive that gives automotive rubber its color also provides tires with other important characteristics.
Automotive tires are black because they contain carbon black. For more than a century, tire manufacturers have added this powdery oil-, coal-, or gas-derived substance to their rubber compounds, turning the naturally off-white substance black.
The Benefits of Carbon Black in Tires
Carbon black acts as a catalyst during the vulcanization process, which turns soft rubber into the more durable and elastic substance we use in automotive tires and elsewhere. It not only prevents the rubber's deterioration by stabilizing dozens of chemical bonds, but it increases the material's tensile strength, or the maximum amount of stress it can bear before breaking. This is obviously a boon for tires, which face constant strain.
Carbon black also draws heat away from the hottest parts of the tire — the tread and belts — so they won't wear so quickly, and it protects against UV damage, further helping to extend the tire's life.
While the inclusion of carbon black in tires has little if anything to do with aesthetics, it provides the nice side benefit of hiding dirt. As the element of the car that touches the road, tires would look filthy after just a few spins were they any other color — particularly white.
How Carbon Black Came to Be Used in Tires
As with many elements of history, how carbon black was first introduced to tires isn't entirely clear. Adding carbon black to tires may have started with Sidney Charles Mote, a chemist for England's India Rubber Company, who in 1904 discovered its value as a reinforcing agent in rubber. Other reports credit BFGoodrich Company chemist George Oenslager for this discovery, saying that the India Rubber Company used carbon black in tires primarily for coloring but didn't initially realize its potential for increasing abrasion resistance.
Once BFGoodrich saw the benefits of enhancing tires with carbon black, it put out a call for a manufacturer that could produce a million pounds of it. Binney & Smith — later renamed Crayola, after its most successful product line — rose to the challenge. The company made a few manufacturing improvements along the way, and BFGoodrich started churning out carbon-black-rich tires around 1912.
Previous to the discovery of carbon black's impact on rubber's durability, zinc oxide was the industry-standard tire-reinforcing additive. Then World War I broke out, and the compound grew scarce because nations needed zinc — a key component of brass — for munitions.
Tire manufacturers needed to come up with something else to strengthen their rubber, and carbon black was the obvious answer. Since it proved superior to zinc oxide in many ways, it became a permanent ingredient in automotive rubber formulations.
Whitewall Tires Were Devised to Save Manufacturers Money
Whitewall tires were actually conceived as a cost-cutting measure. Applying carbon black only to the tread surface saved pennies, and left the sidewalls in their natural, off-white state. The look initially had nothing to do with fashion, but that soon changed, as did the process for manufacturing them.
Rather than compromise the tire by limiting its carbon-black content, enterprising manufacturers simply added a white rubber veneer to the surface of their all-black tires — and charged a premium for it.