NASA's German Touring Series (GTS for short) is a road racing series comprised of six classes of German cars organized strictly based on power-to-weight ratios. This simple formula provides broad flexibility in both vehicle choice and in the modifications allowed (which include just about anything).
The result is a broad range of modifications and extraordinarily close racing.
GTS classes range from GTS1 (with a maximum power-to-weight ratio of 18.5 lbs per horsepower) all the way up through the unlimited GTSU which has no mandated limits.
Drivers are free to meet their specified ratios in any way necessary. Some go for low horsepower and low weight while others feel high horsepower (and the related extra weight) is the hot ticket. Many, of course, split the difference and sit somewhere in the middle. The beauty of GTS is that as a car owner or driver, you can take your best shot at finding a winning combination.
Most GTS cars tend to be either Porsches or BMWs but GTS fields include vehicles from Audi, Volkswagen, Mercedes-Benz, and even the new MINI, which was grandfathered into the series because of it's German parent, BMW.
With large fields of beautiful and well-prepared cars and hard, close, racing, GTS is one of the most popular NASA series with both competitors and spectators alike.