Ferrari have unveiled the first major upgrade to their car which they hope will improve their form following a disappointing start to the season.
Fernando Alonso is testing a revised rear bodywork and exhaust exit design on the final day of the Mugello test.
BBC F1 technical analyst Gary Anderson said: "It looks like a reasonable step forward - you could be looking at 0.2 seconds a lap, possibly more."
Ferrari's work was disrupted when Alonso went off the track.
The Spaniard ended the morning third fastest, behind Red Bull's Sebastian Vettel and Lotus's Romain Grosjean.
Alonso's off-track incident, at the slow Turn 12 after about 90 minutes' running, damaged the front wing. Ferrari said it would take about two hours to repair the car.
The new Ferrari design makes the rear bodywork, in front of and between the rear wheels, much more tightly waisted than before.
It moves the exhaust exits further into the centre of the car, abandoning at least for now Ferrari's attempts to gain an aerodynamic benefit from blowing them at the area where the rear wheels meet the floor in an attempt to 'seal' the diffuser and increase downforce.
But the design has the benefit of having less bodywork obstructing the critical 'coke-bottle' area at the rear, where the bodywork sweeps inwards towards the back of the car.
Anderson, the former technical director of the Jordan, Stewart and Jaguar teams, said: "The exhausts and sidepods are much more conventional now.
"There is nothing too exciting about the exhaust exits, but the 'coke-bottle' is a lot tidier than it was. There is still some upper rear bodywork sticking out into that area but not anywhere near as much as before."One reason there is still some there is that Ferrari are also using that area as an exit for the air from the radiators.
"That is good for cooling the radiators - there is a lot of suction there because of the low-pressure of the coke-bottle area - but if you use it for that, you are compromising the airflow through there."I would prefer the radiator air exit to be at the back of the engine cover where Red Bull had it last year."Having said that, the new Ferrari design is definitely an improvement.
"There is no exhaust interference, and while they're struggling with the car it is better to get rid of that for now and go in search of the bigger gains they need.
"Before, they were chasing the smaller gains from the exhaust but losing much more by compromising overall performance.
"They have a new rear wing due to be run later in the day on Thursday at Mugello and then a new front wing and diffuser which will appear at the next race in Barcelona on 13-15 May."