The suggestion is 400m track but others have said they have got good results on shorter. Best thing to do is to try. Just remember the calibration laps first.
"They also say their algorithm can correctly detect any track as long as it has two parallel straightaways, and either a single or double-radius curve at two ends. "
I tested the Forerunner 945 SW 5.20 Track Mode on a 440-yard track. The watch shows 400m. It appears the smallest distance change displayed is 10m anyway. So the difference between a 440-yard track (402.3m) and a 400m track is less than what the watch will display. Interestingly this is a change from the Beta SW. I tested the Track Mode in Beta SW 5.09 and the watch would display a single meter. The Track Mode still worked great and the real difference in distance and pace is minimal.
