Jerez F1 test: Valtteri Bottas says Williams transformed from 2014

Williams has had an encouraging start to testing at Jerez in Spain this week as it begins understanding its new Mercedes-powered FW37.

After a 2014 campaign where it learned once again how to fight near the front, Bottas says an awareness of what is possible for 2015 has had a big effect.

"The approach is different," said Bottas, when asked by AUTOSPORT how the current attitude in testing compares to last year.

"This team overall is much more confident, because we know that we can make good results and we know that we are a good racing team.

"We can fight for poles and hopefully for wins, and you can sense it. We improved so much from Melbourne to Abu Dhabi in 2014, and it's nearly like a different team really.

"In the end, the approach is about trying to make the most of what we have."

Williams has not seen the need to chase any headline times yet, because it feels its time is better spent understanding the characteristics of its new car.

Bottas added: "There's no reason yet to do any proper performance runs because for us it's much more important at the moment to learn about the new car, getting all the necessary data we need for the guys at the factory to help them to improve with all the aero stuff. First things first."

He also said that it was too early to understand how much of a step forward the new Mercedes power unit was.

"We are still working on engine mapping and throttle maps, all these things. But at the moment we are not taking everything out of the engine and it doesn't feel too different from last year.

"It's getting better and better, and we know that when the time is right to get more out of it than there is potential. I'm confident in what Mercedes have done with the engine and it should be good."