cars, each model of which was designed by the team that used it. After the Split in the 1990s, CART maintained the old formula while the IRL drifted toward the "spec" design that has been the only IndyCar model since 2003 (which changed in 2012, with specialized aero kits available from 2015 to 2017). As engine formulas have changed, and as engine technology has developed over time, F1 cars and IndyCars have each produced more power than the other at different times. But for the foreseeable future, F1 cars will have considerably more power than the spec IndyCar. Alex Zanardi, who drove both in F1 and CART, said that the lighter, naturally aspirated F1 car was more responsive and accelerated off the turns faster, while the turbocharged CART car was more stable and accelerated to top speed faster. More recently Formula 2 drivers Callum Ilott and Christian Lundgaard, who are both also test and reserve drivers for Alpine F1 and Scuderia Ferrari respectively, have stated that the modern Dallara DW12 spec car used in the IndyCar Series sits in between a Formula 2 and a Formula One car on road and street courses in terms of performance. Both Ilott and Lundgaard have stated that the IndyCar's lack of power steering combined with the lower downforce levels and roughly 100 horsepower advantage make the IndyCar harder to drive than a Formula 2 car. Both noted however that around a road or street course the Formula One car would be significantly faster than an IndyCar. There is debate on which series is more demanding. Some point out that champions that retired from F1 have won CART championships: e.g., Emerson Fittipaldi and Nigel Mansell. Drivers who did not excel in F1 have continued their careers in IndyCar with varying levels of success. Some successful IndyCar drivers have tried but failed to get a seat in even a low level Formula One team. A handful of notable IndyCar drivers, however, found subsequent success in F1, including Mario Andretti and Jacques Villeneuve, who became Formula One champions, and Juan Pablo Montoya, who won several F1 races. Conversely, some point to the different track designs of IndyCar (see below) as a bigger challenge to the drivers. Former Haas F1 driver Romain Grosjean stated in 2021 that a modern IndyCar is more physically exerting to drive than a modern Formula One car but that the Formula One