Jenson Button admitted his first laps of Le Mans were "disconcerting" and felt like "another world" to anything he's experienced before.
Like former McLaren teammate Fernando Alonso, Button will make his debut at the famous race on June 16-17. Button is racing for SMP Racing and on Sunday completed 20 laps of the Circuit de la Sarthe, his first sampling of LMP1 machinery at the French venue.
"I was reasonably happy, but in the morning I found it another world -- driving around here in a car I don't really know," Button said. "I found it quite disconcerting. But we made some good changes over lunch, and I was much happier with the car in the afternoon.
"[I had] a lot more confidence. High speed, good confidence, and the braking was much better too. We had quite a lot of 'push' and a lot of the corners here are very tight and they come up on you very quickly, which is very different from what I'm used to.
"I definitely got to grips with it in the afternoon, much happier. But you always want more running, and new tyres. We didn't have enough time, look at the data we have, and hopefully we get some good laps in the Wednesday tests."
Button's team were hampered by a two different car issues which limited track time. The 2009 world champion is partnering former F1 driver Vitaly Petrov and Mihail Aleshin in the Russian outfit. Petrov's quickest time was enough to leave the No.11 car fifth in the overall standings, which were topped by Alonso in the No.8 Toyota.
The Le Mans week includes another test session before qualifying for the race.