Open Menu
Open Menu
 ::

Pirelli looks to the past for its newest tire

Published in blog.hemmings.com

Pirelli’s newest tire, the cross-ply Stella Bianca. Photos courtesy Pirelli.

In 1927, Pirelli debuted its first modern automobile tire, developed from the lessons learned in racing. Dubbed the Stella Bianca, or White Star, the distinctive tread pattern became Pirelli’s signature, and its cross-ply design proved so advanced that the tire remained in production into the 1950s. Now, at the request of classic-car owners, Pirelli has restarted Stella Bianca manufacturing, introducing its first new cross-ply tire in more than 50 years.

The difference between cross-ply (also known as bias-ply) and radial tires lies in their construction. Cross-ply tires utilize bands of cords (today made of polyester or aramid fibers, encased in rubber) that cross over one another, typically at 50-60 degrees to the direction of travel. Radial tires use cords wrapped at 90-degrees to the direction of travel, radially from the tire’s center, in conjunction with reinforcing bands (cap plies and crown plies) that cross at more random angles, nearly parallel to the direction of travel.

Renzo Bassi sketch for 1931 Pirelli Superflex Stella Bianca ad. Image courtesy Fondazione Pirelli.

Cross-ply tires feature sidewalls that are both stiff and strong, but their complex construction doesn’t really help with heat dissipation and, as a result, suffer from increasing rolling resistance and a limited top speed. When pushed to their limits, cross-ply tires tend to deform, reshaping the contact patch and thus limiting traction. Advances in materials and construction have improved cross-ply tires significantly over the years, and they remain the tire of choice for certain off-highway applications. In 1968, however, a study by Consumer Reports showed that radial tires could deliver a more comfortable ride, greater durability, improved fuel economy, and better handing. Though passenger-car cross-ply tires would soldier on for years to come, radial tires would ultimately prevail in this application.

Pirelli Superflex Stella Bianca advertising at the 1937 Finnish Grand Prix. Photo courtesy Fondazione Pirelli.

The first patents for radial tires were issued to an American, Arthur Savage, in 1915, but radials didn’t enter mass production until 1946, when French company Michelin introduced its Michelin X radial. Two years later, the Citroën 2CV became the first automobile designed specifically for radial tires and equipped with them at launch; the first American car to be shod with radial tires was the Lincoln Continental Mark III, which debuted in 1970.

Alberto Ascari, in the number 14 Ferrari 125, leads Giuseppe Farina in the number 10 Maserati 4CLT-48 at the 1949 Lausanne Grand Prix. Photo courtesy Fondazione Pirelli.

From 1927 into the 1950s, however, the cross-ply Pirelli Stella Bianca was the tire of choice for sports cars, racing cars, and even commercial vehicles. Early in the 1950s, Alberto Ascari won the Italian Grand Prix at Monza in a Ferrari shod with Stella Biancas, though by then the Pirelli Stelvio, the replacement for the Stella Bianca, was quickly becoming the tire of choice in motorsports competition. Soon, even this would be surpassed by Pirelli’s Cinturato radial, which favored lighter fabric belts over Michelin’s steel belts. Later, in the 1970s, Pirelli would pioneer the wide, low-profile radial tire, which was specifically developed for the Lancia Stratos rally car. Shortly after, this tire was adopted by Porsche for the 911 as well, and the era of the modern performance radial tire had begun.

With a five-decade gap in cross-ply tire production, gearing up to manufacture the Stella Biancas — which Pirelli will build in Izmit, Turkey — posed the challenge of relearning long-forgotten production techniques. The tires will carry a Corsa tread pattern, with sidewall markings and a Pirelli logo identical to the originals. Inside, the tires will take advantage of modern advances in material science and chemistry, delivering an authentic appearance with capabilities far above cross-ply tires produced in-period.

Pirelli opted to introduce its “newest” tire at the Auto e Moto d’Epoca in Padua, Italy, billed as the biggest vintage-car and spare-parts market in Europe. The Stella Bianca tires will join Pirelli’s Collezione series for classic cars, and will be available initially in a single size, 6.00-16, designed to fit a range of classic sports and racing cars. For further details, visit Pirelli.com/Tyres/En-WW/Car/Collection.