Interesting you should mention that.
On July 10, 2011, on his way to a Cy Young, Verlander's ERA touched 2.15, which was the lowest point it would touch for the season, finishing at 2.40.
Without checking all the records, I would guess that that 2.15 is the best ERA for any Tiger starter at any point in a season after 10+ starts since JV in '11.