By Alan BaldwinTHE holidays are over and Formula One world champion Lewis Hamilton faces a new start as the second half of the season revs up at Belgium’s Spa-Francorchamps circuit this weekend.The rules have been tweaked, meaning drivers on the starting grid can no longer be assisted over the radio by data-crunching engineers to find the optimum clutch settings that will ensure the quickest getaway.Hamilton, 21 points clear of Mercedes team-mate Nico Rosberg after 10 of 19 races, has had three poor starts in a row despite all being from pole position and the big question is what difference the change will make.Another failure in Spa, where the Mercedes drivers started on the front row last year but collided on lap two, would only make the Briton’s bosses more jittery after neither finished on the podium in Hungary in July.Mercedes motorsport boss Toto Wolff warned this week that the team must stay focused.“There is never a moment you can take your foot off the gas and Hungary proved once again that any slip is an opportunity our rivals will grab with both hands,” he said.After hanging out with movie and music celebrities, as well as his dogs Roscoe and Coco, in Barbados, New York and The Hamptons over the August break, Hamilton is raring to get back on track.But he recognised after Hungary, where he finished only sixth while Rosberg was eighth, that the championship could be entering choppy waters – particularly at Spa where rain is regularly a factor.“I expect more unpredictable starts,” Hamilton said then. “I imagine it is going to get worse, but that’s racing.”The key difference is that the clutch ‘bite’ point, hitherto adjusted by engineers after assessing temperatures and track conditions, will be fixed from the moment the cars leave the pit lane.The drivers will then have to determine for themselves the ideal point at which to release the paddles and accelerate away without triggering a loss of traction and wheelspin.Rosberg, who won last season’s pole trophy but has been outqualified 9-1 by Hamilton this year, can sense an opportunity.“There will be more variables and it will be more difficult to predict,” he said. “I like it because it gives me the opportunity to try and beat Lewis in that area. Until now it’s been difficult because it was not really in the driver’s hands.”The German qualified on pole in Belgium last year but the race, on the longest circuit on the calendar, was won by Red Bull’s Daniel Ricciardo.Hamilton, who retired while then-championship leader Rosberg finished second, accused his team-mate of hitting him on purpose “to prove a point” in a controversy that proved a turning point in the season.The fired-up Briton won the next five races and ultimately his second title.“It’s been good to take a break from racing and spend some time relaxing, training and recharging the batteries. But, of course, there’s always that flame in the back of your mind that just wants to get back out there and get on it,” he said ahead of his return to the Ardennes.“Spa is a great track to kick off the second part of the season…I love this track and I’ll be gunning for that top spot again.”Rosberg, winner of three races to Hamilton’s five with Ferrari’s Sebastian Vettel taking the other two, said everything was still to play for.Ferrari will be in the hunt again but Williams also fancy their chances of returning to the podium after failing to score in Hungary.“The layout is normally strongly suited to the characteristics of our car, so I head to this weekend looking for a strong result,” said Finland’s Valtteri Bottas.