Formula One welcomed a new range of tyres with thinner fronts and stronger rears this month - and they could make a big difference to the performance of the cars this season.
When the teams changed from grooved tyres to slicks, the tyres remained the same thickness because some teams had already begun designing their cars around the wider tyres.
This altered the relative contact patches and changed the balance of the car completely because the front tyres had more relative grip than they had in the past. It proved to be one of the big changes that made a difference last season.
One year on, the new narrower Bridgestone front tyres have been developed to effectively put the balance back to normal.
This year it will again see Bridgestone offer four dry tyre compounds that will be known as Hard, Medium, Soft and Super Soft, with two selected per weekend - and the teams have now tried out the final specification of the new front tyre, which is 20mm narrower than the 2009 design.
They used the Soft and Super Soft versions in Valencia for the opening test, while the medium is the main dry compound for both Jerez tests, with teams also having an option to run the Hard and Soft compounds during both weeks if required.
The new narrow front tyres were put to the test straight away, because the graining caused by the lateral forces is a major factor at the Valencia circuit. The Jerez tests, meanwhile, will have rougher tarmac and the severe layout will give the rear tyres a greater test.
It is not only size that matters, however, there is also a significant increase in forces being put through the tyres this year, and that has also made key alterations to the requirements for the new Bridgestones.
Lateral forces in the tyres have increased due to what Bridgestone describes as "a significant" increase in downforce this year, while the ban on refuelling means the cars will be running 100kgs heavier at the start and will also be running longer stints - so the increased fuel weight will place additional loads on the tyres.
The 2010 casing has therefore been designed to be more durable than the 2009 casing, with the rear construction specifically strengthened.
With tyre design fixed at the start of each season, the Bridgestone engineers in Japan were able to go through many different design tyre prototypes last year to ensure they achieved this change in the best possible way.
The teams have also worked with Bridgestone to help supply simulation data so the engineers know the levels of loading the tyres will be put under.