For decades, the Volkswagen Group fit 195/65R15 tires on many of its cars. Almost all of them, until 15-inch wheels went out of fashion, even in lower-spec cars. As with many quirky engineering traits of the VW Group, you can thank Ferdinand Piech for this one.
This fun video from B Sport, a YouTuber with an F1 aero and passenger-car development background, explains why the 195/65R15 found favor at VW. Ferdinand Piech, grandson of Beetle designer Ferdinand Porsche, ran engineering at Audi in the Seventies and Eighties and led development on the innovative third-generation Audi 100, which was sold as the 5000 in the U.S. The 100 used 195/70R15 tires on higher-spec models. It was a tire size favored by Mercedes for offering a good compromise between drag and performance, with good load-carrying capacity.
When he later became Audi CEO, Piech realized that if the company dropped 14-inch wheel options, it would end up buying more 15-inch tires than Mercedes or BMW. This would give Audi more leverage with suppliers, driving costs down and increasing profits. Piech took over the VW group in 1994, and did the same thing, albeit with 195/65R15 tires, whose shorter sidewalls increased handling response.
Soon, tons of Volkswagen, Seat, Skoda, and even a handful of Audi models sported 195/65R15 tires. Higher-performance versions used larger wheels, but a wide swath of VW Group cars were rolling out on these tires. At this point, the cost savings were huge, which helped with Piech's push towards making VW the world's biggest automaker.
Now, of course, you'll struggle to find a car with 15-inch tires, and the push for more options means that VW likely has to buy lots of different tires in different sizes. But you can be sure that, like Piech, there are VW engineers looking for new efficiencies in strange places.