I think Jon was running either the older BT-090's or their replacements, the BT-003's. They are both available in 110/70/17 f and 140/70/17 rear, and it looks like he has either the 140 or 150 on the rear (though I think it is the 140's).
Unfortunately Jon had a very serious on-track accident, but he's working his way back to health.
More info here.