The Swiss team, whose Ferrari-powered C33 has been substantially overweight so far in 2014 at the start of the new turbo V6 era, announced ahead of the Spanish grand prix that its Barcelona upgrade features an "extensive weight reduction".
Auto Motor und Sport correspondent Michael Schmidt said it is in the order of 10 to 15 kilograms.
But he explained that only one Sauber driver will actually enjoy a C33 in Spain that is now below the FIA's mandatory minimum weight of 692 kilos -- the featherweight Esteban Gutierrez.
It is believed the Mexican tips the scales at well below 60kg, while his German teammate Adrian Sutil is reportedly at least 15 kilograms heavier.
Nevertheless, even though Sutil will have no ballast to ideally position around the car, both drivers will benefit from the lighter Sauber, which should be minimally several tenths per lap quicker, Schmidt added.
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