Indy Cars reach higher speeds on ovals than they do on road courses naturally. Formula One cars only race road courses and then, not on any courses that American open-wheelers race on (except for 1/2 of the Indianapolis Motor Speedway going the opposite direction.) Consequently its hard to compare. Both reach speeds in excess of 200 mph and Formula One has the most horsepower coupled with the lightest cars. You would think that would tell the story, however, F1 also have more downforce to help them handle their slow corners. This results in slowing down the car's top speed.

Indy Cars will qualify for this year's Indy 500 with average speeds over 220 mph. Arie Luyendyk qualified in 1996 with an average speed of 236 mph.

Peter Gethin qualified with the fastest time in F1 history at the Italian GP in 1971 with an average speed of 150.754. F1 cars, at the end of a straight, reach a maximum speed of around 212.5 mph (340 kph).

The IRL claim their cars can go from 0-100 mph in under 3 seconds. CART claims 4.2 seconds. The IRL is using new 3.5 Liter normally-aspirated V8 engines this year with horsepower in the 650-750 range. F1 used to use 1.5 liter turbos back in the 80's. Although these cars had over 1000 hp, today's F1 cars go faster with ~830 hp due to advances in the technology of other parts of the race car. CART, while down to 1 engine manufacturer, is at least sticking with their 2.65L Turbo engines which have dropped off in power to about 800 HP.

The tracks as well as the car's engine, suspension, aerodynamics, tires, etc. determine how fast they go. But you must realize that the sanctioning bodies of these race series are often changing the rules, trying to slow the cars down in an attempt to maintain safey and reach a good level of competition.