Other than the intense cold in the morning, conditions were fine, with no rain, and though much of the days was slightly overcast, the sun did eventually break through.
Hamilton was joined by Gary Paffett, as the Woking team focussed on tyre evaluation, with the Circuit de Catalunya providing a more high speed and abrasive surface compared to the previous test sessions.
Today was Paffett's first run in the MP4-23, and it was also his first test without driver aids. As a result the English youngster spent some time during the day familiarising himself with the 2008 package and during this process had a number of spins, contributing to the high number of red flag stoppages.
Ironically - think about it - just 0.6s behind Hamilton was Fernando Alonso in the new Renault. The Spaniard was joined by Nelson Piquet as the French team operated a two-car programme for the first time this year. Both drivers, fresh from their appearance in Paris, where the car was launched on Thursday, were in R28s as the team continues to familiarise itself with the new car.
Alonso had a productive day and concentrated on improving the balance of the car as the track conditions improved. It was the chance to add further miles to the car following a successful shakedown test in Valencia last week. Similarly, Piquet spent the day working on set-up as he continues to adapt to the R28
"It was a really easy programme today," said the Spaniard, "because on the first day the track is always dirty and not in very good condition. You need to run at least one day to get the track into a condition where you can test important things. Today we put some new parts on the car which we had introduced in Valencia, and we tried to evaluate them. Everything was positive and went according to plan, but tomorrow is when we will start the real programme."
"I am still getting used to the car," added Piquet, "so I spent the day trying to find a good rhythm. But we had a few disruptions to the programme, which limited my time in the car and we probably did not get as much done as we would have liked. But this is only the first day of running; we still have two days ahead of us, and Fernando had a good day, which is positive and we are certainly making progress."
"This test was the first time we have run with two R28s," said Christian Silk, "so it was an important day and there was a big effort from everyone. Both drivers had reasonable programmes, but to start with the balance of the car was poor so we had to spend the day working on that. By the end of the day we had found a reason balance and we were quite happy with the performance of the car. Fernando completed most of his programme, but Nelson had a few delays, so we can hopefully make some more progress in the next couple of days."
Following earlier concerns regarding balance, the BMWs appeared much improved today, with both Robert Kubica and Nick Heidfeld in the Top 5. Avoiding the low track temperatures in the early morning (around 6 °C) the German team didn't start 'proper testing' until after 11.00.
Kubica and Heidfeld worked on the set- up of the F1.08 using some new mechanical parts. Although low temperatures and the red flag periods meant that the drivers were unable to do as many laps as originally planned, the changes showed promising results. Robert also conducted several practice pit stops.
Splitting the two BMWs, and thereby prompting suggestions that his team is seeking to impress a potential sponsor, was Giancarlo Fisichella in the Force India. The Italian recorded a best lap of 1:23.015, he also had the 'honour' of completing 100 laps of the circuit, the most of any driver today. His programme focussed on improving set-up and reliability. With no major mechanical problems, the team completed the planned work and will now continue with Tonio Liuzzi tomorrow.
"It was a good day today, " said Fisichella, "I think we made a lot of progress. We did some runs to work on set-up and looked at some parts to improve reliability and had no big problems over the day. I felt more comfortable in the car too - we are definitely going in the right direction and the times were pretty good. I'm very happy as we're showing the potential we have now.'
"A very productive day of testing that was only spoilt by the numerous red flag periods we experienced," said Mike Gascoyne. "The car ran reliably with no real problems and we completed a full programme of set-up and reliability work. As you can see, we have made good progress with Giancarlo and can count this as a very pleasing day. We now have to maintain this with Tonio and Adrian over the next two days.'
Toro Rosso continues to impress, with Sebastian Vettel enjoying a slight advantage of his teammate, Sebastien Bourdais. The Frenchman worked on evaluating a new front suspension set-up, while also running through a race weekend scenario, practicing pit-stops and other elements of F1 that will be new to him this season. Vettel spent his day evaluating brake materials and also going through some race situations.
It was a bleak day for Williams. An accident involving Nakajima caused the Grove outfit to bring its test to an abrupt halt as it investigates the cause. As previously reported, the Japanese driver went straight on at the first corner, slamming into the barriers. Although unhurt, Nakajima was a perplexed by the cause of the accident as his team, there is also concern that the new asphalt surfaced failed to slow his car.
Red Bull had two RB4s available for the first time, with David Coulthard given the job of giving the latest chassis its shakedown, before moving on to general set-up work, which was also the main item on the agenda for Mark Webber. Running a different Bridgestone tyre to the last test, conditions were complicated by extremely cold weather, especially in the morning.
While many here are focussing on the inevitable Hamilton/Alonso 'battle', the Milton Keynes team attracted much attention with a controversial airbox cover (above and below) which bore a resemblance to a device run by March back in 1973.
Other than its effectiveness in terms of aerodynamic benefit, it remains to be seen whether the FIA might rule it as being outside the (aesthetic) rules of the sport. After all, it's happened before.
Following the launch of the Honda RA108 at Brackley on Tuesday, the 2008 car took to the track in its new livery for the first time at Barcelona today. Worryingly, both Rubens Barrichello and Alex Wurz were to be found at the foot of the timesheets at the close of play.
The Brazilian completed a couple of acclimatisation runs early in the morning session before putting the new car through its paces as he worked through various set-up changes over the course of the day, completing 55 laps in total.
Wurz had his first opportunity to experience the new car as he drove the second RA108 for his second day of track action with the team following an outing in the RA107 in Valencia last week. The Austrian put the new chassis through an initial shakedown programme today covering 26 laps.
Jenson Button will join the team tomorrow to take over the car from Wurz, with Barrichello continuing for a second day of running.