In the toughest formula in world motor sport the difference between being on the pace and off it can be the result of tiny miscalculations in design in any one of thousands of components that make up Formula One’s complex modern race cars.

All the teams in the pitlane battle with tantalisingly tricky design dilemmas, not least the perennial midfield teams, Toyota or Honda for example, who despite spending untold millions cannot seem to make the leap to the top table. But perhaps most aware of how fragile and easily corrupted the design process can be are teams such as Williams and Renault, who have enjoyed spells of glory only to see their cars fall off the pace.

Last season, it was Renault’s turn to take a cold shower as the French manufacturer slipped to fourth on the track after two consecutive world drivers’ and constructors’ titles in 2005 and 2006. The team were secretive about their problems at the time but have now given a full explanation of what went wrong and how the genesis of their design failings went all the way back to midway through their second championship-winning season in 2006.

Renault were battling three areas of performance deficit last season. They had lost their star driver in Fernando Alonso; they were struggling with the switch from Michelin rubber to the standard Bridgestone tyres, and most critically, the team were becoming aware that something had gone wrong with their design process and the way data generated in their wind tunnel matched — or failed to match — real life experience on the track.

Bob Bell, the Renault technical director, sketches in the background: “The aerodynamics of an F1 car are very complex because the vehicles themselves are geometrically very complex,” he said. “The regulations make them that way — exposed wheels, cars running low to the ground and aerodynamic devices, the wings and so on, which are absolutely pushed to the limit of their performance. But you can only push these things so far and there are boundaries. If you step over them, you dramatically lose performance.”

Midway through 2006, the aerodynamics team at the Renault base in Enstone near Oxford went over this invisible frontier without realising it and started producing a generation of components that looked good in the wind tunnel but did not work on the track.

“We just stepped over the threshold with the design of some of the aero devices, some of the wings, some of the diffuser features which tipped us over that edge,” Bell said. “The wind tunnel was still saying ‘this is good’ but actually, on the track, in the real world, the car was bouncing around.” First to be “infected” was the R26 and Alonso was only just able to hold on at the end of 2006 to clinch a second world drivers’ title from a resurgent Michael Schumacher in the Ferrari. If Bell and his colleagues were suspicious that they had an underlying problem, their fears were confirmed when they launched the R27 in early 2007 and realised the season ahead would be a write-off. “It was a pig, it lacked grip,” Bell said. “For the drivers it was difficult to set up, it was inconsistent from one corner to the next and it suffered balance changes from high to low speed through a corner.”

The big question was where the problem lay and to start with the team threw themselves off the scent, blaming their sudden loss of performance on the new Bridgestone Potenza tyres and the loss of Alonso to McLaren Mercedes. “We were able to naively convince ourselves for a little while that it wasn’t necessarily an aero issue,” Bell who was forced to look a lot deeper, said. What then occurred was a sort of Formula One designer’s detective story as he and his staff went back through every component, comparing wind tunnel data with track performance until they nailed the point at which matters had gone awry. “The most difficult thing about it all is that it is very easy in a situation like this to overreact,” Bell said, “and to look at the effect of the problem and deal with that as opposed to the cause.

“What we said was ‘forget ’07’ — it’s too late. The car is irretrievably bad. What we have to do is find out what caused this problem, what the effects are, rectify the cause and then, once we’ve done that, apply that to getting the best we can out of the ’07 car. But, more importantly, make sure the ’08 car doesn’t suffer from any of these problems.’ ” Given the insidiousness of the problem, Bell is proud of the methodical way in which the team set about rooting it out and recovering from it.

He believes that Renault have made up much of the ground they had lost even if — in his view — the French manufacturer will not be fighting for championships this year. “Renault grew out of Benetton and has an experienced cast of players who have seen good times and bad times, good budgets and bad, and it has developed an intuitive feel of what you need to go racing,” Bell said. “We are cost effective, good natural racers. Last year, we had a technical problem and we are proud we stuck together and pulled ourselves out of it in a sensible and sound way.”

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