When looking at the speed charts on INDYCAR Race Control, you’ll notice that there are two different speed charts. The reason for that is that INDYCAR looks at two different speeds: tow speed and no tow speed.
The tow speed is the speed that is most often reported when looking at the speed charts. The tow speed is the most common speed seen on race day, and refers to when cars are close together in a draft.
Drafting, also known as split streaming, refers to the aerodynamic impact on the car when driving closely behind another car. The lead car reduces the drag (air resistance), which reduces the power required from the car behind needed to maintain speed.
Simply put, a line of cars can travel faster than a car on the open track by itself.
The no tow speed is the speed a car is traveling in the open, by itself. To give an (drastic) example: at the time of this writing Charlie Kimball is fifth on the speed chart with a top speed of 227.477 mph. When we look at the no tow speed charts, we see he is in 28th (only 29 cars have seen track time so far today) with a no tow speed of 218.488.
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In a race setting cars will always travel faster in tow than they will out of it. No tow speed is a good thing to look at in practice to see how powerful a car can be on the open track. However, questions can be raised when there are such drastic differences in both speeds. Recently Andretti Autosport drivers have accused Chevy teams of sandbagging on practice speeds.
Practice for the 100th running of the Indianapolis 500 continues today through 6 pm and continues tomorrow from noon to 6 pm. Qualifying for the race takes place Saturday and Sunday at Indianapolis Motor Speedway.