Marc VDS Honda’s Jack Miller reaped the rewards from an early switch to slick tyres to end first practice for the French Grand Prix fastest from Marc Marquez.
The 4.2km Le Mans circuit began to dry as the preceding Moto3 session drew to a close, though the track still was not in the right state for sick tyres. However, as FP1 entered its final few minutes, several riders ditched their wet rubber.
One of them was iffy weather specialist Miller, who immediately felt comfortable on his soft front and rear Michelins, going top by a considerable margin. The Australian continued to chip away at his best time, eventually ending on a 1m37.467s to go 1.2s clear of the field.
Marquez left his switch to slicks late, but he too felt comfortable straight away on them and jumped up to second ahead of home hero Johann Zarco, who will be hoping to celebrate his re-signing with the Tech 3 team for 2018 with a debut MotoGP podium on Sunday.
Cal Crutchlow moved up to fourth on the timesheets in the closing stages, with Loris Baz completing the top five ahead of fellow satellite Ducati GP15 runner Karel Abraham. KTM opted to sit much of the session out, the Austrian marque keen to avoid unnecessary risk in the unrepresentative conditions.
Bradley Smith ventured out onto circuit on his RC16 in the final minutes and went seventh fastest. Slotting into eighth was Yamaha’s Valentino Rossi, who spent much of FP1 languishing outside of the top 20.
The Italian still did not look comfortable on his YZR-M1 when he switched to slick tyres. Indeed, he was 3.4s off the pace and only 0.4s quicker than tenth-placed team-mate Maverick Vinales, who stayed on wet tyres for the entire 45 minutes.
Between the Yamaha duo came the second Aspar Ducati of Alvaro Bautista, whilst Andrea Iannone, Jonas Folger, Dani Pedrosa, Andrea Dovizioso and Danilo Petrucci rounded out the top 15. Suzuki stand-in Sylvain Guintoli was 20th in his first official MotoGP outing since 2011.