This weekend, approximately 200 of the world’s best cyclists will begin competing in one of the most challenging sporting events in the world: Le Tour de France.

Le Tour is widely regarded as the most prestigious cycling race on the planet and this year more than 10 million international spectators are expected to flock to see the race first-hand. Tens of millions more will watch the race live on TV.

The 98th edition of the great race will run from Saturday until July 24 and will see 22 teams of nine riders cover more than 3,400 kilometres in 21 stages in search of the coveted maillot jaune: the yellow jersey, awarded to the rider who completes the course in the shortest overall time.

Ticket to ride

The first 11 stages of the 2011 Tour will cover 1916.5 kilometres of flat-lands and medium mountains of France’s north west.

The favourites for the yellow jersey – such as three-time winner Alberto Contador, Andy Schleck and Australia’s Cadel Evans – and other riders who prefer the highroads will use their drafting and tactical skills to minimise their energy expenditure in these opening stages.

By doing so, they will be able to head into the mountains in the race’s second half (from stage 12) with a minimal level of fatigue.

Come together

On the flatter roads, most riders will ride together in a big group (known as a peloton) which will move at approximately 40 km/h. At such high speeds, the primary force for riders to overcome is air resistance.

By positioning himself in the middle of the peloton, a rider can substantially reduce the air resistance he experiences, thanks to the shielding effect of riders ahead of him.

This shielding effect means he can move at the same speed as a rider who has his face in the wind at the head of the peloton while enjoying a 30% reduction in the amount of power needed to travel at such a speed.

Thanks to this aerodynamic advantage, riders in the peloton will enjoy many periods of recovery during which they won’t have to produce any more than 100 watts – a power output that even a recreational cyclist can maintain for long periods of time.

All together now

Riding in the middle of the peloton provides some aerodynamic advantage but it also creates an element of risk for riders.

If the peloton happens to split into smaller groups at any time, a rider in the middle of the peloton might lose contact with riders closer to the front.

To avoid this risk, every rider will have to repeat high-intensity efforts (up to 600 watts) between 15 and 30 seconds in length every time the peloton speeds up, so that he will always remain less than a bike-length behind the rider ahead of him.

If the front of the peloton realises that some riders have lost contact with them, they can immediately decide to speed away. In that case, the chasing riders will be forced to work very hard if they want to rejoin the head of the peloton.

By putting themselves in such a situation, chasing riders will ruin their chances of saving energy on the flatter roads.

Don’t pass me by

For sprinters, missing a breakaway could mean missing the chance to win the stage.

This is big deal because, as well as the overall classification (yellow jersey), there’s also a prize for the rider who accrues the most “sprint points” throughout the three-week event. That prize is the maillot vert or green jersey.

Some points are available at pre-determined points along each stage but a stage win provides the most points for riders gunning for the green jersey.

For the yellow-jersey-favourites, missing a breakaway could mean losing precious time they will then have to win back in the mountains and the individual time trial (organised on the second last stage).

The second risk associated with riding in the middle of the peloton is the chance of being involved in a crash. With riders in the peloton being very close to one another – within arm’s reach much of the time – one crash toward the front of the field can have a domino effect further back.

A bad fall can compromise the chance of an individual finishing the race and his team’s overall strength.

Because of these risks, you’ll see the yellow jersey favourites all riding a few bike-lengths from the front of the peloton. There, they’ll be shielded from the worst of the wind resistance, while still being able to react to a breakaway if necessary.

With a little help from my friends

In the final 20km of the flatter stages, teams with the strongest sprinters – riders such as Mark Cavendish, Thor Hushovd and Tyler Farrar – will move toward the front of the peloton.

If a bunch of riders managed to breakaway from the peloton earlier in the day, the sprinters' teams will increase the speed of the peloton to more than 50 km/h.

On most occasions, this increase in speed will see the breakaway riders “swept up” by the peloton, while also preventing any new breakaways from forming toward the end of the stage.

In these final kilometres every team will rely on a few helpers – riders known as “domestiques” – to bring their best sprinter to an optimal position around 200 meters before the finish line.

(This optimal position will usually be one or two bike-lengths from the front of the group, for the aerodynamic reasons mentioned above.)

The final part of the sprint will last approximately 10 seconds, during which the sprinters will produce a staggering 1500 watts or more, attempting to be the first to cross the line.

The long and winding road …

By stage eight, riders will be entering the medium mountain stages of the Massif Central, in southern-central France.

Here you’ll see the climbing specialists and contenders for the yellow jersey come to the fore, preparing their bodies for the approaching high mountain stages in the Pyrenees and the Alps.

More on that soon …

This is the first in a two-part series about the science of competing in the Tour de France. The series will conclude in a few weeks time, with a look at the high mountain stages and the final days as riders approach the finish line in Paris.

Will you be watching the Tour de France? Why/Why not?