According to a detailed case study published by Harvard Business School (HBS) in 1983, to get the 500 into production before competitors, Firestone "used modified bias-belted tire
production equipment to manufacture its SBR sites.
The closed plants were mainly bias and bias-belted tire operations that were made obsolete by the conversion to radial tires.
The introduction of the radial has helped induce the closing of old and inefficient plants embedded with technology designed for bias and bias-belted tires.
tire manufacturers pushing bias-belted tires
until they could catch up with Michelin's radial tire construction aspects.
Bias-belted tires, like bias tires, have multiple plies of nylon or fabric and at least two steel belts under the tread.
In bias and bias-belted tires, strength is increased by adding more body plies.