BMW sports boss Mario Theissen has claimed the company has been held back during its partnership with Williams.
BMW will take Sauber's place on the Formula One grid next year
The German manufacturer is ending its engine partnership deal with Williams and will run its own Formula One team next year after buying Sauber.
"For the past five years we pushed with Williams but never felt that we fully accomplished," said Theissen.
"That was when we started to evaluate the option to create our own team - to have control of all success factors."
The relationship between BMW and Williams started in 2000 but has deteriorated this season.
But although the partnership is drawing to a close, Theissen insists BMW is determined to go out on a high.
"There is still one third of the season to go and Sir Frank Williams and myself are pushing very hard to close the gap to the front-runners," he told formula1.com.
"Success is the best way when it comes to a goodbye. We want to finish the partnership on a high, not on a low. And we are all working very hard to achieve this."