Class 1 Touring Cars
Class 1 Touring Cars refers to two generations of prototype silhouette-style touring car regulations employed by the FIA. First generation. The first generation was a production-based formula introduced in 1993 along with Class 2 Touring Cars, the latter officially becoming known as Super Touring cars from 1995. Class 1 permitted more liberal modifications to the vehicles than those allowed for Class 2 cars. These Class 1 regulations restricted engines to a maximum of six cylinders, 2.5 litres capacity and four valves per cylinder. The basic unit had to be derived from a production engine  made in quantity by the same manufacturer as the car, although it did not have to be from the same model as that being raced and could be extensively modified. All-wheel drive, traction control, anti-lock brakes and electronically controlled differentials were permitted. Aerodynamic aids were free below the wheel centreline and, from 1995, suspension systems could be purpose built rather than production based. Class 1 Touring Cars contested the Deutsche Tourenwagen Meisterschaft series from 1993 to 1995, the International Touring Car Series in 1995 and for the International Touring Car Championship in 1996. Only three manufacturers, Alfa Romeo , Mercedes-Benz and Opel, competed in Class 1 during the short history of the original category (Audi and BMW had built cars based on the B4 80 Quattro and E36 M3 respectively for the class, but never raced them) and the withdrawal of Alfa Romeo and Opel from the International Touring Car Championship at the end of 1996 effectively spelt the end of the class. Second generation. In early 2014, the DTM and the Japanese Super GT Series began a co-operation agreement in which the two series would begin to merge their technical regulations. This led to an official  tie-up in September of the same year, with plans for the DTM to move to 2.0-litre inline-4 engines by 2017. Aerodynamic alterations were agreed in 2015, with the seeds sown for potential joint-races between the series. Later in the same year however, the regulation changes were postponed to 2019 given DTM manufacturers' reluctance to potentially engage in more costly development. Super GT would also delay the implementation of the regulations to 2020, as the final regulations were signed off in 2018. The second generation of Class 1 Touring Car is a purpose-built racer based on a  two-door road-going model. The cars feature a two-litre turbocharged inline-four engine, capped at 650 hp and mounted in the front of the car. Push-to-pass and DRS are employed on the DTM vehicles (but not in Super GT), which benefit from 3.4t of downforce. All vehicles must be front-engine, rear-wheel drive. The first Class 1 cars debuted at the 2019 DTM Hockenheim round. DTM and Super GT conducted joint-races at the end of 2019, however both saw the previous generation Super GT GT500 cars enter. Aston Martin, entering DTM for the  first time through the new regulations, concluded their program after a single season with constructors R-Motorsport claiming the cars were too expensive. Audi followed suit by announcing their departure from the series for the 2021 season in April 2020. The DTM eventually abandoned the regulation set after just two seasons and switched to a GT3–based formula from 2021.