Germany's Auto Motor und Sport said arguably the biggest development of all was seen on the Red Bull, whose designer Adrian Newey "has once again read the rules perfectly".
The report said the development is a sort of "double floor", opening up beneath the sidepods to improve airflow to the rear of the diffuser.
Sebastian Vettel set the fastest time of Friday with the new rear end.
"We still have to go through the data," team boss Christian Horner is quoted as saying, "but the feedback from the drivers was positive.
"We will probably use the new parts for the rest of the weekend."
At McLaren, Lewis Hamilton was using a further evolution of the MP4-27's new rear suspension.
"We hope that tomorrow we will have the parts for Jenson (Button)'s car," said team boss Martin Whitmarsh.
And Ferrari kept up its strong recovery from the F2012's early problems, running on Friday with new front wing end plates, engine cover, floor and exhaust.
"If the parts work, they stay on," said a spokesman for the Italian team. "If not, we will optimise them for Silverstone."
Fernando Alonso sounded confident.
"In the last four races, every new part we have brought works as we expect from the wind tunnel. That is something we struggled with in the last two years," he said.