Marco Andretti leads first day of 2016 Indianapolis 500 practice

Andretti led a quartet of Andretti Autosport Dallara-Hondas on the speed chart with a fastest lap of 228.978mph around the 2.5-mile Indianapolis Motor Speedway on a cool and cloudy day.

Carlos Munoz was second at 228.945mph followed by 2014 Indy 500 winner Ryan Hunter-Reay's 228.033mph and Manor Formula 1 reserve Alexander Rossi's 226.865mph.

"These were picture-perfect conditions today," Andretti said. "Next week will likely be warmer, so it's too early to read much into things today."

With rain in the forecast the team decided to switch its testing schedule to get in more track time on Monday than normal.

"I think that's why we look pretty stout right now," Andretti added.

"By Fast Friday you'll see things where they really pan out across the field.

"I'm pretty happy with the behaviour of the car but there's some work to do still.

"The thing about this track is you can be on top one day and then have to completely start over the next."

Four-time IndyCar Series champion and 2008 Indy 500 winner Scott Dixon was the fastest Chevrolet runner in fifth at 226.835mph.

"We tried a number of things today with the car but no one is going for big numbers this early out there," said the Ganassi driver.

Andretti's additional entry Townsend Bell was sixth and the fastest driver not aided by a tow with a lap at 226.724mph.

"We are still settling in," he said. "It's still early but I'm getting to know the guys and I'm pleased with the direction we are heading in."

All 33 cars that are entered took practice laps on Monday, including the most recent official entry driven by 1996 Indianapolis 500 winner Buddy Lazier.

It was also a day for the rookie drivers to get through the mandatory rookie orientation programme before they were cleared to participate in practice.

Rossi, Max Chilton, Spencer Pigot and Matt Brabham all passed ROP with ease.

With only 33 car/driver combinations entered there will be no bumping this year as all are assured of making the race.

A full day of rain is expected on Tuesday, with temperatures then increasing later in the week.

FIRST PRACTICE RESULTS: