When did the US go metric with their races?

Question

I'm from Australia. Back in the 80s or 90s, the US started changing to metric but then it faded out. Now I'm seeing broadcasts (e.g. Champ Car )where they're converting track length to kilometres and average speed in km/h. Has the US decided to go fully metric? Yes, it was US and not Canada races I saw!

Answer 1

don't know about champ car, indy or f1, but nascar is still in miles and mph.