Sonoma IndyCar: Penske's Helio Castroneves leads first practice

The Brazilian's lap time of 1m17.330s deposed championship leader and Penske team-mate Simon Pagenaud's early 1m17.850s mark from just his second lap.

Both 2016 championship contenders completed just a handful of laps in the opening session as they preferred to concentrate on the more representative conditions of practice two later on Friday, run at a more similar time to Sunday's race.

Pagenaud put in just five laps, with rival Will Power touring the sun-soaked Californian asphalt just four times, echoing the low mileage of fellow Penske drivers Castroneves (four laps) and Juan Pablo Montoya (eight laps). Power cited the track's tendency to use up tyre grip within just two-or-so laps.

Marco Andretti posted the second-fastest time, 0.131 seconds down on Castroneves.

Graham Rahal and Jack Hawksworth were next, while Ryan Hunter-Reay made it two Andretti cars inside the top five.

Mikhail Aleshin put in a fast lap towards the end of the session to end up sixth, with Josef Newgarden, Takuma Sato, James Hinchcliffe, and championship hopeful Pagenaud completing the top 10.

The uninterrupted practice session contained little drama, although 13th-fastest Tony Kanaan had a scary moment with around 25 minutes to go in the session, catching a big snap of oversteer as he crested the hill towards the Carousel corner.

Low mileage for Power resulted in the Australian ending the session in 17th place, just ahead of fellow Antipodean racer Scott Dixon, who won at the track 12 months ago to seal his fourth IndyCar championship.

PRACTICE ONE TIMES: