Rahal Letterman Lanigan Racing driver Graham Rahal ended second IndyCar practice at Road America at the top of the timesheets.
He put in a 1m43.022 mid-way through the session, bouncing back from a difficult practice one in which electrical issues hampered his running.
Team Penske's Will Power just missed out on the top spot in practice two, finishing 0.138 seconds behind Rahal's best time.
Tony Kanaan and Juan Pablo Montoya made late improvements to move up to third and fourth.
Kanaan was one of several drivers to take to the grass run-off areas around the Road America circuit, with the Chip Ganassi Racing driver going straight on and across the gravel at Turn 2 with half an hour to go.
Carlos Munoz and Max Chilton were next up, with Helio Castroneves, Scott Dixon, Ryan Hunter-Reay and Indianapolis 500 winner Alexander Rossi completing the top 10.
Josef Newgarden returned to action on Friday after suffering a fractured right clavicle and wrist in a huge crash at the Texas Motor Speedway two weeks ago.
He was 13th quickest in the afternoon, behind Takuma Sato and Marco Andretti
Newgarden was granted permission to complete practice but will undergo further tests to determine if he will race in Wisconsin.
Practice one pacesetter and current IndyCar championship leader Simon Pagenaud put in the most laps of anyone in the second session, with 19, but he finished down in 15th.
The planned 75-minute session was shortened by 90 seconds following a late red flag for Jack Hawksworth's stranded AJ Foyt Dallara-Honda at Turn 4.
|1||Graham Rahal||Rahal Letterman Lanigan||Dallara/Honda||1m43.0224s||-||19|
|2||Will Power||Team Penske||Dallara/Chevrolet||1m43.1608s||0.1384s||15|
|3||Tony Kanaan||Chip Ganassi Racing||Dallara/Chevrolet||1m43.7031s||0.6807s||12|
|4||Juan Pablo Montoya||Team Penske||Dallara/Chevrolet||1m43.7427s||0.7203s||14|
|5||Carlos Munoz||Andretti Autosport||Dallara/Honda||1m43.7699s||0.7475s||15|
|6||Max Chilton||Chip Ganassi Racing||Dallara/Chevrolet||1m43.7964s||0.7740s||16|
|7||Helio Castroneves||Team Penske||Dallara/Chevrolet||1m43.8137s||0.7913s||18|
|8||Scott Dixon||Chip Ganassi Racing||Dallara/Chevrolet||1m43.8423s||0.8199s||12|
|9||Ryan Hunter-Reay||Andretti Autosport||Dallara/Honda||1m43.8425s||0.8201s||10|
|10||Alexander Rossi||Andretti Herta||Dallara/Honda||1m43.8530s||0.8306s||15|
|11||Takuma Sato||AJ Foyt Enterprises||Dallara/Honda||1m43.8702s||0.8478s||17|
|12||Marco Andretti||Andretti Autosport||Dallara/Honda||1m43.8885s||0.8661s||14|
|13||Josef Newgarden||Ed Carpenter Racing||Dallara/Chevrolet||1m43.8937s||0.8713s||15|
|14||Sebastien Bourdais||KVSH Racing||Dallara/Chevrolet||1m43.9059s||0.8835s||14|
|15||Simon Pagenaud||Team Penske||Dallara/Chevrolet||1m43.9625s||0.9401s||21|
|16||Jack Hawksworth||AJ Foyt Enterprises||Dallara/Honda||1m43.9679s||0.9455s||18|
|17||Conor Daly||Dale Coyne Racing||Dallara/Honda||1m44.0070s||0.9846s||16|
|18||James Hinchcliffe||Schmidt Peterson Motorsports||Dallara/Honda||1m44.0419s||1.0195s||15|
|19||Mikhail Aleshin||Schmidt Peterson Motorsports||Dallara/Honda||1m44.1000s||1.0776s||18|
|20||Gabby Chaves||Dale Coyne Racing||Dallara/Honda||1m44.2901s||1.2677s||17|
|21||Charlie Kimball||Chip Ganassi Racing||Dallara/Chevrolet||1m44.4625s||1.4401s||15|
|22||Spencer Pigot||Ed Carpenter Racing||Dallara/Chevrolet||1m44.9342s||1.9118s||17|