Pirelli's new range of tyres for 2014 is more conservative, according to the whispers from private testing in Bahrain.
The testing of next year's tyres, which will have to handle the much-higher torque of the new turbo engines, is taking place behind closed doors, and laptimes and details are not being disclosed.
But Italy's Autosprint said: "The general indication is that they (the tyres) are slower.
"Even with the same (2013) cars, the laptimes are expected to rise, because the tyre supplier is taking a more prudent approach."
Pirelli had a tumultuous 2013 season, characterised by the tyre-exploding British grand prix and constant complaints about questionable durability and quality.
Autosprint said F1's official tyre supplier has taken "dozens" of compound and construction combinations to Bahrain, but they all have one thing in common -- the internal kevlar belt.
"The experiment with steel belts, which gave so many problems at the beginning of 2013, is over," the report added.