Tyre concerns emerge at Mercedes for Hamilton and Bottas

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Mercedes' Lewis Hamilton and Valtteri Bottas put in a mammoth day of running on Tuesday in Barcelona, and while it was a productive session overall, there was however one issue of concern.

The German squad split its workload between its two drivers with Bottas running in the morning and Hamilton taking over in the afternoon, with a combined 177 laps put on the Mercedes board on a day.

Both men admitted they were still getting acquainted with their new W09 Silver Arrows, but they nevertheless shared a common concern with regard to Pirelli's medium and soft tyres which were put to the test on a day when drivers finally enjoyed relatively normal air and track surface temperatures.

Driver line-ups for Day 6 of pre-season testing in Barcelona

"In these weather conditions we start to really work the tyres and we had a few issues to manage," explained Bottas.

"So we had a few more challenges with the tyres than we had last week, but at least now they can warm up.

"We keep discovering more about the new car, learning how it reacts to different settings. We did more than 80 laps - so more than a race distance, a really good mileage."

On the subject of tyre compounds, Hamilton echoed his team mates observations, but also reiterated his belief that the Circuit de Catalunya's fresh new asphalt was not doing Pirelli or Mercedes any favors.

"The biggest challenge we faced today was to get the tyres working properly on this new track surface", said the four-time world champion.

"The medium tyre was difficult to get working; the soft tyre is better for warm-up, but suffered with degradation. We are learning all the time.

"It's been a good day. We've got through everything we needed and put good mileage on the car - it's been productive."

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Phillip van Osten

Motor racing was a backdrop from the outset in Phillip van Osten's life. Born in Southern California, Phillip grew up with the sights and sounds of fast cars thanks to his father, Dick van Osten, an editor and writer for Auto Speed and Sport and Motor Trend. Phillip's passion for racing grew even more when his family moved to Europe and he became acquainted with the extraordinary world of Grand Prix racing. He was an early contributor to the monthly French F1i Magazine, often providing a historic or business perspective on Formula 1's affairs. In 2012, he co-authored along with fellow journalist Pierre Van Vliet the English-language adaptation of a limited edition book devoted to the great Belgian driver Jacky Ickx. He also authored "The American Legacy in Formula 1", a book which recounts the trials and tribulations of American drivers in Grand Prix racing. Phillip is also a commentator for Belgian broadcaster Be.TV for the US Indycar series.