Sonoma IndyCar: Helio Castroneves heads all-Penske Friday top three

Fresh from finishing quickest in practice one, Castroneves set a 1m16.6678s lap - 0.0394 seconds quicker than title-chasing team-mate Will Power.

Championship leader Simon Pagenaud ended the 75-minute session third, having set the first lap in the 1m16s early on.

Ryan Hunter-Reay snuck into the top four to top the Honda contingent, 0.3891s down on Castroneves' time.

The Chip Ganassi Racing quartet was the surprise of the day having struggled throughout.

Only Charlie Kimball and Max Chilton made the tail end of the top 10, while experienced hands Tony Kanaan and Scott Dixon ended their frustrating sessions 14th and 16th respectively - the latter experiencing a bizarre spin on the exit of Turn 2 near the end of the afternoon.

The Turn 9 chicane caught out plenty of drivers, with the likes of Indianapolis 500 winner Alexander Rossi and Spencer Pigot getting out of shape on the kerbs, while Chilton and RC Enerson were among those to miss the corner entirely on hot laps.

The practice's only red flag came from a late engine issue for Dale Coyne Racing's Conor Daly, who parked his Dallara-Honda at the bottom of the hill on the exit of the Carousel after billowing smoke along the straight.

The former GP3 and GP2 driver had reported losing speed on the straights following a misfire before rolling to a stop and ending his day in 22nd.

PRACTICE TWO TIMES: