Heidfeld: Renault debut a 'fun' day

On his first day in the R31, Heidfeld edged out Ferrari's Fernando Alonso to set the quickest time late in the afternoon.

"I really enjoyed the day," said Heidfeld. "It was fun driving the car, although it obviously takes time to get used to things when it's your first time in a car and working with a new team.

"We had a good day, without too many problems, and luckily all the changes we made to the car went in the right direction and improved things, so I was able to push harder and harder."

He played down the significance of his rapid pace.

"In terms of the lap times, it's very difficult for me to compare with the other teams because we don't know the fuel levels or what the others were doing," Heidfeld insisted.

The German was also calm in his assessment of the potential of the Renault, which had been fastest at Valencia last week with Kubica at the wheel.

"My first impressions of the car were positive, although there are always areas where you can improve," said Heidfeld.

Renault had indicated that Heidfeld would get the nod to stand in for Kubica provided today's test went smoothly.

The team is still expected to give reserve driver Bruno Senna a run tomorrow.