Confirmation of Jenson Button’s shock move to McLaren surprised the Formula One world last week and the World Champion has been forced to defend his extraordinary decision. Leaving Brawn is a massive risk for Jenson and there is no obvious single reason for his unexpected career change. Button has said that he wants to set himself “fresh challenges” but his full rationale is likely to be more complicated.

Some of Button’s fans believe the move is motivated solely by money, or that Jenson was dazzled by the bright lights of McLaren. Others suggest his management mistakenly forced him out of Brawn during contract negotiations, or that Mercedes pushed him aside in favour of an all-German line up. It’s also been touted that Jenson simply has new ambitions as reigning World Champion and is keen to prove himself against Lewis Hamilton.

The truth is that Button’s move is a combination of several different factors and only those close to him know the full story.

The suggestion that Mercedes, the new owners of Brawn, pushed Jenson aside in order to create a German superteam is wide of the mark. Mercedes has been a partner to McLaren for fifteen years and has never demanded that a German driver be part of their team. In addition to that, they have already signed Nico Rosberg for 2010 which is enough to give them all the national attention they’d want. They don’t need a second hometown driver alongside Rosberg. Also, the publicity gained by having an all-German team would be outweighed by the publicity of having the reigning World Champion on board, so it is very unlikely they would ditch Button for the sake of patriotism.

However, there is a genuine possibility that Jenson was pushed out by Ross Brawn. A number of UK newspapers have reported that Brawn grew tired with Jenson’s extended contract negotiation tactics and eventually left him with no option but to join McLaren.

Brawn made a contract offer to Button after he sealed the World Championship but Jenson felt the offer did not reflect his true value. The deal could have made Jenson one of the highest earning drivers in F1 but the pay was largely performance based and was not a guaranteed salary.

After this final offer was presented to Button, he visited the McLaren factory and let the details of his meeting become public. If Jenson was doing this to leverage more money out of Brawn (as many suspected at the time) it failed dramatically. Ross Brawn and Nick Fry were apparently so incensed with Jenson they withdrew their offer citing a breach of contract. This effectively left Button with nowhere to go but McLaren.

If Jenson had been planning to join McLaren all along it would not have been a problem, but if he was hoping to retain the option of staying with Brawn he may have out-negotiated himself.

Either way, he is better off financially at McLaren where much of his pay will supposedly come from a regular salary.

There is some talk that Jenson made the switch based solely on money, and it would seem that McLaren will pay Button more over the next three years than he would have earned at Brawn/Mercedes. Money was definitely a factor in Jenson’s decision. During the negotiation process his management team repeatedly talked about Jenson wanting to feel “valued” and noted they weren’t happy with the financial terms of Brawn’s offer. They rightly claimed they weren’t being greedy, but at no time did they suggest Jenson would like to seek a new challenge or refresh his career, which only came out after he signed the deal with McLaren.

Whilst money was a big factor, it wouldn’t have been the only reason for Button’s switch. Moving to McLaren is a risk and could ruin Jenson’s value in the long term, so if he was going for money alone he might have been better off taking the safer option at Brawn/Mercedes. Besides, Jenson doesn’t exactly need the cash so is not going to jeopardise his whole career and reputation so he can buy another Bugatti Veyron.

The salary on offer at McLaren might have been very attractive, but the prestige and history of the team was probably a bigger influence on Button’s decision.

McLaren is one of the two biggest teams in Formula One and has 20 championships to its credit. They have the best facilities in the sports history and displayed their enormous depth of engineering talent throughout 2009. At the start of this year McLaren had one of the slowest cars on the grid, and whilst that isn’t a great advertisement for the team’s success, they finished the season with a solid race winner. Only a team with the resources of McLaren could turn around their form so quickly and in such dramatic fashion. They will be very competitive throughout 2010, and if McLaren hits another rough patch in the years ahead, they will be able to recover. Jenson might have joined McLaren because he knows he will almost always have a decent car.

He would not have made the jump to a smaller team regardless of what they paid him.

Jenson will also relish the challenge of winning the world title for a new team. Other drivers have switched teams to refresh themselves, and whilst Button did not seem to be getting tired at Brawn, it might be part of the reason for his move. Juan Manuel Fangio remains the only driver in the F1 record books to win two consecutive championships for two different teams so Jenson might be after a little piece of history.

Jenson Button said himself that he wanted a new challenge, and he could not have come up with a bigger one than beating Lewis Hamilton in a McLaren. Lewis started racing with the Formula One team three years ago and has been part of their development program since he was 13. Beating Lewis would make Jenson a legend and that will be the attraction to racing alongside him.

Whilst Lewis is the clear favourite to hand Button a drubbing in 2010, it might not be so straightforward.

If Jenson was ever going to topple Lewis in the same machinery, next year will be his best chance.

Refuelling is banned in 2010 meaning drivers will only have to pit for tyres. This will give a big advantage to those who can look after their rubber and Jenson does this better than almost everyone else. Button is incredibly smooth behind the wheel and is so fast because he doesn’t slide the car or push it beyond its limits. At Monaco this year a number of drivers suffered from blistered soft tyres very early in the race. By the end of the first stint Jenson had built a ten second lead over Rubens Barrichello, and that was all due to tyre wear. Rubens had been just as quick as Jenson all weekend but could not match his tyre management skills. That is a significant point given Rubens was sometimes able to beat Michael Schumacher through being kinder on his machinery.

Lewis, on the other hand, is very hard on his tyres. Many of his stunning pole laps, like the one he secured at Abu Dhabi, are full of locked brakes and oversteer and that is how he generates his speed. Hamilton is one of the hardest, if not the hardest driver, on his rubber. At the 2007 Chinese Grand Prix he chewed his wet weather tyres so badly they wore down to the canvass. Lewis also had to adopt a compromising three stop strategy at the 2008 Turkish Grand Prix because Bridgestone were so concerned his harsh driving would result in a puncture.

Lewis is a professional and will be able to adjust his style accordingly for next year’s regulations, but it won’t come as naturally to him as it does for Jenson. Hamilton might be quicker than Button but he isn’t smoother, and that could be worth a lot in 2010.

Also, Jenson likes a car that understeers – the polar opposite to Hamilton that likes a twitchy responsive set up. This works into Jenson’s favour because next year Bridgestone are reducing the width of their front tyres. When Formula One moved away from grooved tyres the cars developed a disproportionate amount of grip at the front. The teams have been able to overcome this but now Bridgestone are addressing the imbalance and are taking some of the extra grip away. In theory, this should benefit the drivers who like understeer because teams will have to work harder to make the cars turn in.

Button could be making the move to McLaren at just the right time.

In twelve months from now we’ll know for sure. Jenson will either finish 2010 as an all conquering hero, or a man who wrecked his career when it was just starting to peak.

We’ll certainly have much better insight regarding his decision to join McLaren in the first place.