Red Bull's Newey says 2012 constructors' win was 'most tiring'.

Red Bull design chief Adrian Newey said his team's constructors' title victory this season had been the "most tiring" of their three.

Sebsatian Vettel's second place behind McLaren's Lewis Hamilton in Austin on Sunday tied up Red Bull's third consecutive constructors' crown.

Newey said: "It's been exhausting just to keep up. It feels a long season."

He said it had been "very satisfying but a lot of hard work" to turn a difficult start to the year around.

Red Bull have always had strong race pace this season but they struggled for the first two-thirds of the year to consistently replicate it in qualifying.

It was only a significant upgrade to the car at the Singapore Grand Prix at the end of September, and continuous tinkering ever since, that had enabled them to suddenly qualify regularly at the front.

From that position Vettel won four consecutive races in Singapore, Japan, Korea and India to take the drivers' championship lead from Ferrari's Fernando Alonso and make Red Bull unassailable in the constructors'.

Newey said the team's problems had been caused by the banning of last year's must-have technology, exhaust-blown diffusers, which Red Bull exploited better than most.

"Last year's [constructors' title] was obviously the easiest," Newey said. "In comparison to 2010 [this year] has obviously been different. In 2010 we had a lot of silly points losses at the start of the year from reliability, driver mistakes and so forth but the car had very good pace. This year pace-wise it has been very close through the year.

"We struggled a bit at the start of the year, or the mid-season more than anything, to understand the car and get it to work properly.

"I think it bore out my pre-season fear that having been on side exhausts for two years and really developed the car and the whole philosophy of the car around that technology.

"To have it taken away over the winter was probably a bigger step back for us than other people."

Asked if the drivers' or constructors' title was more important to him, Newey said: "In some ways the constructors' [is my preference] because we are on the construction side, but to me they are both important and we like to achieve the double if we possibly can.

"To choose between constructors' and drivers' I find very difficult. To achieve the hat-trick is very special. [I was] lucky enough to achieve it at Williams and again here at Red Bull. It is a great tribute to everyone in the team."

He added that the team could "afford ourselves one night of celebration…but with the drivers' still open and Brazil a week away we can't afford to get too obliterated tonight".

Team boss Christian Horner said: "We're halfway there, we have closed out one championship, to have won a third consecutive constructors' [title] is something we could only have dreamed about a few years ago.

"To have achieved what we have against the opponents we have in only our eighth year in the sport is something quite remarkable.

"It is testimony to the long hours, dedication and determination in the team, and it is something every member of the team is fiercely proud of."