Not much. The top speed for controllable driving in a wheeled vehicle is in the 300mph range. The power and aerodynamics requirements to step up to 400mph are s

Not much. The top speed for controllable driving in a wheeled vehicle is in the 300mph range. The power and aerodynamics requirements to step up to 400mph are severe. Specifically, the wheel-driven land-speed record is a bit over 400mph (although just last year it climbed up to 440mph) and the vehicles capable of going that fast are nearly incapable of taking turns of any significance at those speeds. Jet powered vehicles are capable of going faster, even mach 1, but they have the same controllability problems. If we were to hypothesize a future extreme sport of ultra fast racing in the 300mph or 400mph speed range then a few problems become immediately apparent. First, you'd need a specially designed course with very gradual turns. Also the roadway would have to be kept immaculately clean of debris. Second, the races would not last very long due to high rates of fuel consumption. For example, the Bluebird CN7 consumes fuel at top speed at about 260 gallons per hour (and has a 25 gallon tank), while the ThrustSSC consumes fuel at a rate of 24 gallons/mile. Third, passing would be extremely dangerous because even disrupting another vehicle's aerodynamics in any way, let alone physical contact, could cause it to become uncontrollable resulting in a very damaging and life threatening crash.