The blog Son of the South Bronx today posted that IndyCar race from Brazil on May 5 drew a 0.20 TV rating with 224,000 viewers on NBC Sports Network. View post. I couldn't find another source to confirm the number. Last year's race in Brazil generated a 0.33 TV rating with 348,000 viewers.
The highest rated program on NBC Sports Network for the period of April 29 to May 5 was a playoff hockey game that generated a 0.4 rating with 580,000 viewers, per Son of the South Bronx.