Formula 1 has not yet found a technical solution to enhance driver visibility during wet conditions.
Last year, initial tests of wheel covers or 'mudguards' aimed at reducing spray plumes behind the cars were unsuccessful.
Working with the FIA, Ferrari tested improved fenders on the artificially-watered Fiorano track last week.
"Several variants were tested, both on the front and rear axles," reported Auto Motor und Sport.
"However, the pictures taken by paparazzi at the side of the track do not indicate that a significant improvement has been achieved," added correspondent Tobias Gruner.
"The fear is that it's not only the large wheels, but also the huge diffuser of the modern ground effect cars that sucks the water from the asphalt and whirls it into the air," he said.
"And the rear end of the underbody cannot be covered as easily as the wheels," Gruner explained.
"The FIA will probably have to carry out a few more tests before a satisfactory solution is found. Until then, we must hope that the rain gods will be kind to Formula 1."
