This weekend's Hungarian grand prix is the first race since the sport's official supplier scrapped its policy of leaving a gap between the compound stiffness of its two available tires.
But BMW-Sauber driver Heidfeld said after Friday practice: "I'm afraid the tires are still not really good."
The German press report said many drivers support the 32-year-old's view, regarding the inconsistency of the 2009-spec slick tires. He also said the tires are too sensitive to ambient and track temperatures.
"Tiny differences can have a large effect," Heidfeld commented, revealing he has made his opinion "forcefully" known to the Japanese manufacturer.
"But nothing happens," he added. "Whatever Bridgestone makes is always going to win."