Pirelli begins testing on wider tyres to be used in 2017
Formula 1 supplier Pirelli has started on-track development work on the wider tyres to be used from next season.
Ferrari are testing at their Fiorano test track on Monday and Tuesday before Red Bull take over at Mugello in Italy on Wednesday and Thursday.
The new tyres are 305mm wide at the front and 405mm at the rear, 60mm and 80mm wider respectively than in 2016.
Ferrari are running their 2015 car modified to simulate 2017 downforce levels.
The rules to be introduced next year are aimed at making the cars up to five seconds a lap faster.
This will be achieved by increased levels of aerodynamic downforce, including a greater proportion created from the underbody, and different front and rear wings, in addition to the wider tyres.
In addition, Pirelli have been told to produce tyres on which drivers can push flat-out for much longer periods.
The current Pirelli tyres require careful management and can only be driven on the limit for a lap or two at a time before they overheat and irretrievably lose performance, so drivers are lapping at least a second off the pace for the vast majority of races.
Ferrari's test is primarily aimed at trying out Pirelli's new wet-weather tyres, although four-time champion Sebastian Vettel did some installation laps on the untreaded 'slick' dry-weather tyre early on Monday.
Haas' Esteban Gutierrez, who was Ferrari's reserve driver in 2015, takes over on Tuesday.
As part of the attempt to simulate 2017 aerodynamic loads, the car they are driving is fitted with side 'skirts', which seal the gap between the floor and the track and increase downforce.
'Skirts' were part of F1 from 1978-1982, the era of so-called 'ground effect' aerodynamics, before being banned on safety grounds before the 1983 season.