Hamilton got 91 laps under his belt yesterday afternoon after team-mate Valtteri Bottas notched up 86 laps in the morning session.
Last week, snow in Barcelona played havoc with Mercedes’ testing.
However, pictures from the pit lane showed how much punishment the soft and medium rear Pirelli tyres took during practice.
And Hamilton has explained why this could be the biggest problem for the team going forward.
“The biggest challenge we faced today was to get the tyres working properly on this new track surface,” Hamilton said.
“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.”
Bottas was in full agreement with Hamilton as he said: “In these weather conditions we start to really work the tyres and we had a few issues to manage.
“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.”
Testing concludes on Friday with the new F1 season getting underway on March 25.