SAO PAULO, Brazil - Former heavyweight boxing World champion Frank Bruno has given Australian F1 driver Mark Webber the benefit of his advice on “when to call it quits”.Red Bull’s Webber, 35, said on Saturday ahead of the season-ending Brazilian GP that he had "bumped into" the British boxer, who fought Mike Tyson and Lennox Lewis, at the gym.'SOME ARROGANCE INVOLVED'"He's been through quite a few things and he's been very honest with me the last few times I've gone up there," Webber said. "He told me 'the biggest fight you will have in your career is when you try to stop'. And that's how it is for all of us."That's how competitors are - there's some arrogance involved that we want to keep competing."Webber has a fresh racing contract with Red Bull but was speaking in relation to Brazilian Rubens Barrichello's determination to keep racing for a 20th season. His words, however, suggested retirement had also been on his own mind. The Australian hasn’t won a race in 2011 after being a title contender right to the last the previous year in a campaign dominated by German team mate Sebastian Vettel - now a double World champion.'MAKE SURE YOU'RE READY'McLaren's Jenson Button, 31, who recently signed a new multi-year deal with his team, agreed the question of when to call it quits was rarely straightforward."You have to make sure you're ready to leave. If you leave too early and try and come back... a lot of us don't think it will work, It's a difficult call... not something you take lightly."Germany's seven-times World champion Michael Schumacher, who retired in 2006 after a record-breaking spell with Ferrari, returned in 2010 with Mercedes but has yet to step back on the podium.He will be joined on the grid for 2012 by another driver making a comeback; McLaren's 40-year-old Spanish test driver Pedro de la Rosa has signed with HRT. Stay with Wheels24 for the F1 weekend.