Mark Webber admits he finds motivation harder as the clock ticks down on F1 career

The Australian, who announced in June that he will race sportscars for Porsche in next year's World Endurance Championship, told Sky Sports News that he isn't enjoying F1 as he once had.

"I think towards the end of your career, you probably find little things that convince yourself that you're not enjoying it as much as you were," said Webber, who made his F1 debut in 2002.

"You're not 22 anymore and that's obvious; I'm 37 and I've done over 215 races at the end of the year, so the juice goes out of the tank a little bit.

"But at the end of the day, I'm still super-respectful of who I'm racing against and how I go about it. I'm still not blasé about competing at this level; I still respect it at this level. But there comes a time when you've got to get that decision right."

Webber has to date won a total of nine grands prix and came closest to winning the World Championship three years ago.

He was well-placed going into the final race of the 2010 season in Abu Dhabi but it was team-mate Sebastian Vettel who triumphed instead.

"If I'd won the Championship in 2010, that might not have been the best decision, if I'd retired then. But it didn't happen," Webber added.

Vettel has since gone on to claim three more World Championships, with the most recent sealed in India at the weekend.

The German has consistently outperformed Webber, with the latter admitting that the switch to Pirelli tyres in 2011 hasn't helped.

"Little did I know what we were in for, probably, with the switch in tyres from Bridgestone to Pirelli," Webber said. "That was another thing; it's up to the drivers to get your head around that and sort that out, but even within the same tyre family - you can see it now with [Lotus team-mates] Kimi [Raikkonen] and [Romain] Grosjean - when you have these slight changes in tyres and how they can really affect the drivers' performance.

"That's been magnified on the Pirellis quite a bit in my opinion, through different driving styles and techniques and things like that.

"That hasn't helped I don't think - the top-flight edge of getting the most out of yourself week in, week out."

Even so, Webber feels fortunate to be able to drive cars designed by Adrian Newey, whose latest creation - Red Bull's RB9 - is the tenth to have won the constructors' title.

"Adrian Newey is still probably on the biggest reasons I continue to drive, because to drive his cars is still very, very rewarding," he added.

The Abu Dhabi Grand Prix is live only on Sky Sports F1 this weekend - coverage begins with the Drivers' Press Conference on Thursday at 11am