Helio Castroneves was quickest in a busy second IndyCar practice session at Sonoma on Saturday.
Several drivers took turns at the top of the timesheets before Penske's Castroneves made it his own with a fastest lap of 1m18.6582s, although his time was very nearly beaten right at the end by Ryan Briscoe, whose best effort fell just 0.0338 seconds short.
Briscoe's late run knocked first practice pacesetter Ryan Hunter-Reay back to third, with Scott Dixon and Will Power rounding out the top five.
Several of the earlier session leaders faded back as others around them put on new tyres, including Juan Pablo Montoya, who was quickest with 20 minutes to go and finished up eighth-fastest, and Marco Andretti, who ended the afternoon in 10th.
The session was the final chance for preparation ahead of qualifying, which is scheduled for later on Saturday afternoon.
Pos Driver Team/Engine Time Gap Laps
1. Helio Castroneves Penske/Chevy 1m18.6582s 16
2. Ryan Hunter-Reay Andretti/Honda 1m18.6920s +0.0338s 18
3. Ryan Briscoe Ganassi/Chevy 1m18.7984s +0.1402s 12
4. Scott Dixon Ganassi/Chevy 1m19.0304s +0.3722s 13
5. Will Power Penske/Chevy 1m19.0370s +0.3788s 14
6. Sebastien Bourdais KV/Chevy 1m19.1105s +0.4523s 16
7. Josef Newgarden Fisher/Honda 1m19.1565s +0.4983s 17
8. Juan Pablo Montoya Penske/Chevy 1m19.2052s +0.5470s 13
9. Tony Kanaan Ganassi/Chevy 1m19.2305s +0.5723s 15
10. Marco Andretti Andretti/Honda 1m19.2617s +0.6035s 15
11. Carlos Munoz Andretti/Honda 1m19.4005s +0.7423s 15
12. Charlie Kimball Ganassi/Chevy 1m19.4245s +0.7663s 17
13. Simon Pagenaud Schmidt/Honda 1m19.4422s +0.7840s 13
14. Justin Wilson Coyne/Honda 1m19.4487s +0.7905s 18
15. Takuma Sato Foyt/Honda 1m19.5128s +0.8546s 14
16. Graham Rahal Rahal/Honda 1m19.6190s +0.9608s 19
17. Mike Conway Carpenter/Chevy 1m19.6458s +0.9876s 19
18. Sebastian Saavedra KV/Chevy 1m19.6898s +1.0316s 16
19. James Hinchcliffe Andretti/Honda 1m19.7831s +1.1249s 17
20. Mikhail Aleshin Schmidt/Honda 1m19.8133s +1.1551s 16
21. Carlos Huertas Coyne/Honda 1m19.8398s +1.1816s 19
22. Jack Hawksworth Herta/Honda 1m19.9912s +1.3330s 18
All drivers use Dallara chassis