I just saw the Bristol NASCAR race yesterday. JJ won.....Anyway, the Bristol track is basically a roundy round without much of a straightaway, and like you said, it is short. I believe it's the shortest track that NASCAR races on. I would guess between 1000-12000 laps. Depending on the constant speed, it could go further, but if you are talking about 70 MPH, then my guess will be close I think.