Michelin XAS: Design
The Michelin XAS was the first asymmetrical tire to be developed in 1965, and also the first tire to reach the H speed rating of 131 mph (210 km/h). The Michelin XAS was developed in a very outside-the-box manner, the asymmetrical tread and casing with differences on the inside and outside of the tire is built to take into account the different work done by the shoulders, sidewalls and different parts of the crown as the R&D team at Michelin worked out that different areas of the tire have different functions. They had flipped the symmetrical tire norm and instead, they were focusing on each individual part of the tire and focusing on improving the function of each of those parts. Think of it working like your foot. It's asymmetrical, the inside and outside work differently to give good balance and (In the car's case), sure handling. Many race cars prior to the production of the XAS were racing on Michelin X's, which at the time Michelin hadn't endorsed their tires as race tires.
The XAS truly does compliment a sports car in so many ways. With outstanding hold on the road on bends, exceptional stability, and unmatched grip in all conditions at the time, all this plus being the first standard tire with a 131 mph (210 km/h) H speed rating at the time, made it the best choice for any sports car both at the time, and in the modern days, as they have become classic sports cars.
Michelin XAS History: Formula France
The Michelin XAS was already a race-worthy tire with it's brand new speed capabilities in the H speed rating and it's exceptional performance quality, but with the creation of Formula France in 1968, the technical and sporting regulations needed a tire. Michelin developed an XAS in a special race compound that was specially developed for racing. It became the race tire used for Formula France. Named the Michelin XAS FF, this was used in hill climbs, rallies, and of course, circuit racing.
Michelin XAS History: Triumph
The XAS' incredible handling caught the eye of Triumph. They had fitted a 165HR15 XAS on their Triumph TR6 as it had exponentially improved the handling in a way that didn't require much work. Triumph were so impressed with the improvement to the handling that they in turn downsized the tires on the Stag, which had originally fitted 185R14 tires, but following the improvement on the TR6, the upgrade was made to a 175R14 Michelin XAS as the standard fitting from 1976 onwards.