Despite the odd positive drugs test, cycling is considered to be a much cleaner sport now, which is universally welcomed. But has that affected speeds in the Tour de France?

A Wiggins win in the Tour de France was a first for British cycling and widely celebrated as a triumph for "clean" racing, after a series of negative headlines.

Two incidents highlighted the issue during this year's race - Frank Schleck tested positive for diuretics and withdrew, maintaining his innocence, while Remy di Gregorio was suspended after police questioned him on suspicion of using banned substances.

Earlier this year, former Tour winner Alberto Contador had his 2010 title taken away and was banned for two years after testing positive for clenbuterol in that year's tour. In June, the US Anti-Doping Agency charged the retired seven-time winner Lance Armstrong with using performance-enhancing drugs. Armstrong denies the allegations.

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Add to this the admission by former winners Bjarne Riis, Floyd Landis and British cyclist David Millar that they took performance-enhancing drugs in the past and it is easy to be cynical about today's tour. Millar completed his ban in 2006 and is now an outspoken anti-doping campaigner who won one of the Tour de France stages in this year's race.

But if you look at the data from this year's Tour are there any signs it is cleaner than before?

The obvious place to look would be at the speeds of the riders over the years.

The climb up Alpe d'Huez is one of the toughest on the Tour. In the late 1990s it was being completed in around 38 minutes, three minutes quicker than last year.

The problem with this year is that there is no Alpe d'Huez climb. There is another problem too. A lot of things impact on speed, particularly the wind but also whether you are riding in someone's slipstream and the speed of the riders you are trying to beat.

Another measure which might make a better comparison, according to Dr Ross Tucker of the sports science institute at the University of Cape Town, is the power-to-weight ratio.

Dr Tucker says you can see a marked difference between today and the bad old days when there were no tests for blood doping or drugs such as EPO.

"In the late 1990s and early 2000s if you were going to be competitive and win the Tour de France you would have to be able to cycle between 6.4 and 6.7 watts per kilogram at the end of a day's stage.

"What we are seeing now, in the last three or four years, is that the speed of the front of the peloton [of] men like Bradley Wiggins, Chris Froome and Vincenzo Nibali, is about 10% down compared to that generation and now the power output at the front is about 6W/kg."

He says that they should actually be getting faster, not slower, because of advances in technology and sports science.

There are probably fewer people doping, and those who are doping are doing it less severely Dr Ross Tucker, Sports science institute, University of Cape Town

He thinks that what we are seeing now is a human race as opposed to the pharmaceutical races we saw in the past.

"The physiological implications of riding 6.5W/kg are for me, as a physiologist, beyond belief. What they are doing now is physiologically plausible."

But not everyone agrees that the upper limits of power to weight ratio should raise suspicion. Dr Auriel Forrester is a sports scientist who works for SRM. They are the company that supply the data tracking equipment to most of the teams in the Tour de France. She is more interested in the variability of a rider's performance.

"We can plot the best power a rider can produce over one second, two seconds, five seconds, two, three, four hours and you will see a logarithmic decline in their power output."

She says that using this data you can build up a clear picture of a rider's power profile. You can then compare this to a power profile for a particular stage and see whether they are riding normally.

As you can imagine, this sort of data is closely guarded by the top riders but one, Nibali, has released data for his Stage 11, on Thursday 12 July. This is the ride from Albertville to La Toussuire, which includes three stiff climbs.

Who is Bradley Wiggins? Born in Ghent, Belgium, Wiggins and his mother Linda moved to England in 1982 after her split from his Australian father Gary, himself an endurance cyclist. Before long, the two-year-old would be seen tearing around the Dibden House estate in Maida Vale on his first bicycle. Having received it as a Christmas present, he immediately demanded the stabilisers be removed. Has three Olympic gold medals from track cycling, and London 2012 beckons BBC Sport: Wiggins - the making of a Tour de France champion

Dr Forrester says his data shows that he is riding consistently. His first two climbs are done at 320 and 322 watts and the final ride is 360 watts. This means on the final climb his power to weight ratio is 5.2W/kg. "Those figures are where you expect that rider to be."

She also says that - being privy to the secret data - if you compare Nibali to the other riders when they have been climbing, his figures are comparable.

"They're all ballpark, similar figures. None of those would stick out as spurious."

We do not have data for the same stage in the past but she hypothesises that we may have seen similar figures for the first two climbs but then you would have seen power outputs of 400W for the final hill.

It was this kind of effort which characterised the Tour de France in the 1990s and early 2000s that should have raised suspicion. It might be why some commentators say this tour was boring because the riding was more measured.

In the past, when riders have been doping they have had two things - a bit more in the tank at the end of the day and the ability to recover more quickly. This means that a rider who is doping can launch an attack on the first-placed rider without having to worry about recovering for the next stage. Today, riders have to pace themselves more carefully across the entire Tour.

Dr Tucker thinks that the anti-doping measures that are now in place are squeezing out the cheats but he is not convinced they have gone altogether.

"What is happening is there are probably fewer people doping, and those who are doping are doing it less severely."