Valtteri Bottas says he's learned a lot in the off-season and feels a more complete driver heading into 2016.

The 26-year-old has been racing in Formula One since 2012 and has collected eight podiums on the way to back-to-back top five championship finishes. But Bottas now believes he has reached a new level both physically and mentally.

"I feel more complete as a driver than in any previous season so far because you always keep learning," he said. "It's a new season, a new start. I had a good winter, training and improving my physical condition and I'm feeling better than ever."

The Finn also feels confident on Williams' pace ahead of the Australian Grand Prix and is hopeful of once again challenging up the front.

"From testing to here we brought some upgrades and if they work as expected, that will help us to be closer and challenge for podiums. I already feel comfortable in the car and hopefully that will mean good results."

After a pair of scraps with compatriot Kimi Raikkonen last year, Bottas has fired a warning to the Ferrari driver and the rest of the field that he won't be backing off on-track.

"I don't want to give room to any other driver when I'm racing, especially this year when I want to race for better positions. I'm definitely not going to give up in any situation when I feel I have a realistic chance to gain a position or defend my position."