Hamilton says being world champion will not sink in until the first race of the season
Lewis Hamilton admits the raft of technical changes in Formula One will make retaining his title even harder.
Of all the new regulations being implemented for 2009, the Kinetic Energy Recovery System (Kers) presents constructors with the biggest test.
Kers stores energy that would normally be lost during braking and converts it into power.
Hamilton said: "There are lots of unknowns which makes it even harder to predict once the season starts."
Some drivers have already announced they would prefer to run without Kers, while others have voiced safety concerns, but Hamilton is happy with the system in his car.
Speaking to the official F1 website, he said: "Of course, there are safety concerns but I'm extremely comfortable with the way McLaren have approached the Kers programme.
"I can tell you everything related to Kers has been designed with safety in mind, so I'm happy that our car will be safe.
"And the way you use it will vary from track to track. Maybe some teams won't run it at every race.
"But I like it - it's something else to play with in the cockpit, and that's not a bad thing.
"Of course, unlike the engines, which are frozen, Kers development will continue throughout the whole season so it's an area where the teams will be making advances on a regular basis."
Kers is not mandatory, and some teams have so far reserved judgement on whether they will use it at the season-opening race in Melbourne on 29 March.
One man who may not currently share Hamilton's opinion on the new technology is Kimi Raikkonen, whose Ferrari had to stay in the pits for over three hours on Tuesday because of a problem with the system during testing in Bahrain.
Despite the problem, Raikkonen ended the day fastest in testing ahead of Jarno Trulli of Toyota by about one tenth of a second, with BMW Sauber's Nick Heidfeld further behind.
Overall, Hamilton announced himself pleased with McLaren's pre-season testing in Jerez, Spain, and believes he may cut a more relaxed figure during the forthcoming season.
He said: "Obviously, becoming the champion does take some weight off your shoulders but I don't really look too closely at it - I'm just spending every moment focusing on 2009.
"Winning the world championship in Brazil seems such a long time ago now - things move so fast in Formula One, even when you're not at the racetrack.
"To be honest, I don't really think of myself as world champion yet - I think that will finally sink in when I get to Melbourne for the first race - so I don't put any extra pressure on myself to live up to that."