This year the Tour has two big stories: Lance Armstrong and Mark Cavendish.

Armstrong's comeback to the sport has eclipsed almost everything else in the sport this year. As a seven-time Tour winner, cancer survivor and globalbrand, he casts a huge shadow over his rivals, even in his own Astanateam.

Can he win an eighth Tour and, more importantly, how will the 37-year-old cope with the rigours of the race after a three-year absence from the sport?

And that's without even mentioning the fascinating rivalry with hisown team-mate, Alberto Contador, winner in 2008 and the favourite forthis year's yellow jersey.

One thing is certain: Armstrong isn't turning up just to make up numbers. His stated goal may be raising cancer awareness but no-one doubts that he would passionately love to win an eighth Tour.

His presence may evoke cycling's past for his critics but it also guarantees that this year's Tour will be followed by one of the biggest press corps in its history.

The fastest man on the planet, Cavendish could surpass Chris Boardman'sBritish record for professional race wins during the Tour. He's the hottest property in cycling at the moment and, having won four stages last year, all eyes will be on the 'Manx Express' in every one of the 10 stages that could finish in a bunch sprint.

He claims his goal is simply to reach the finish line in Paris rather than be acontender for the green jersey, awarded to the winner of the pointscompetition and frequently the prize for the best sprinter.

Confused as to why that means he won't win the race overall? Allow us to help demystify the race a bit.

Albert Contador is favourite to win the 2009 Tour

A leisurely 3,500 km (or 2,175 mile) bike ride around France andneighbouring countries. That's roughly the distance from London toCairo or Tel Aviv and an incredible 15m people line the route.

Asmany as 180 riders will set off from Monaco in 20 teams, but many willhave dropped out by the time the race finishes on the Champs Elysee inParis on 26 July.

By then, the survivors will have taken part in 21 gruelling stages with only two rest days to nurse their aching limbs.

They will average a staggering 40km/h (25 mph) over the course, often ridingmuch faster than that. On mountain descents, some riders have claimedto have reached speeds of up to 110km/h (68 mph).

No. There are four different types of stage, each with its own particular challenges.

TOUR BY NUMBERS 10: Fewest number of Tour finishers - in 1919 34: Most stage wins - by Eddy Merckx (pictured above left) 41.654: Fastest race average in km/h - by Lance Armstrong in 2005 (above right) 118,000: Total calories burned by Tour finisher (equivalent to 26 Mars Bars per day)

Flat:

Ten of this year's stages take place on "flat" roads. This doesn't mean they are without undulation (in fact, they often include climbs that would terrify a club cyclist). But they invariably feature most of the competitors riding together in a big "peloton" (or pack) for 200km (or 125 miles) and can end in one of twoways: with a breakaway victory by an individual or small group; or,typically, with a hair-raising bunch sprint.

Neither of these scenarios have much of an impact on the overall standings of the race because breakaways are always chased down by the peloton if theycontain serious contenders and bunch sprints result in all or most ofthe field being given the same time for a stage.

Victory or a high place generates prize money and contributes towards the pointscompetition. It also allows riders to pay back their sponsors withmuch-desired TV time which is vital for small teams and riders withlittle chance of glory elsewhere in the race for the big prizes.

Individual time trial:Every man against the clock. These are shorter stages of around 50 km.But lots of time is won and lost as Tour challenges flourish or falter.The last-placed rider starts first, followed two minutes later by thenext highest, and this carries on until the race leader starts.

Team time trial:Every team against the clock. The clock stops on the fifth rider tocross the finish line. Traditionally longer than the individual timetrial, they are the ultimate test of the strength of the team.

The nine riders rotate at the front of the line to keep the pace up. Itrequires incredible discipline and co-ordination to do it well and someteams will have spent many hours practising for it. Like the individualtime trial, it may not win the Tour for an individual rider but a poorperformance can certainly lose it, leaving them with minutes to make upelsewhere in the race.

Mountain: Most Tours are won in the mountains. And mountains come in all shapes and sizes, with climbs rated four, three, two, one or "hors" category, the latter being thesteepest. Climbing from sea level to 2,000m (often more than once in aday), separates the men from the boys and one bad day can cost hugechunks of lost time.

The main contenders have to be able to stay with the specialist climbers on the ascents while the sprinters rely on the descents to stay within the cut-off time for the stage. Hill-top finishes tend to create big gaps in the field as they expose the differences between those who can climb and those battling to staywithin the time limit for the stage.

The biggest prize in cycling is a yellow jersey in Paris. Thissignifies overall victory in the Tour de France, an honour won seventimes by Lance Armstrong and five by Jacques Anquetil, Eddy Merckx,Bernard Hinault and Miguel Indurain. There are also smaller awards tobe won, each denoted by a different coloured jersey to help spectatorsspot the category leaders.

GUIDE TO TOUR LANGUAGE Peloton: "Herd" or pack Domestiques: "Servants" or team helpers Grimpeur: Climber Maillot Jaune: Yellow jersey Voiture balai: Broom wagon - rounds up stragglers and boots them out of the race

Yellow: This is the jersey everyone wants. If you are in it,you are the overall race leader on aggregate time since the start ofthe Tour. It often changes backs a few times, particularly during theearly flat stages of a Tour. But it normally finds its final restingplace after a time trial or a gruelling hill-top finish in the Alps orPyrenees. This year the fabled Mont Ventoux in Provence on the Tour'spenultimate day is the one that the organisers hope will provedecisive. Tour champions need to be good at both climbing and timetrialling.

Green: The points prize goes to the most consistent stage finisher and is normally worn by one of the best sprinters in the field. With a sliding scale of points available to the first finishers on any day, contenders for this jersey bunch at the front of the peloton for dangerous sprints on flat stages. They alsoneed to show tactical acumen to stop their opponents picking up theadditional points available at the intermediate sprints along the day'sstage. They just try to survive the mountains.

Polka dot (red and white):Conversely, King of the Mountains contenders live for the climbs. Theytend to be slimmer in build and bounce up slopes to pick up the pointson offer to the first riders over every hill. This is the only jerseyever to have been won by a British rider, Robert Millar who earned thetitle in 1984 when he finished fourth in the overall classification.

White: This goes to the best-placed young (under-26) rider in the general classification.

Rainbow:This is not up for grabs in the Tour, but can be seen on the back ofthe World Road Race champion (if he's not wearing yellow, of course).Country champions also have the right to wear national instead of teamcolours.

In addition, there are three related awards available, one of them of dubious distinction:

Combativity:The cyclist who is deemed to have put in the bravest show on a stagewins the right to wear a white-on-red race number (as opposed toblack-on-white).

Lanterne Rouge: This is the mocking moniker for the last-placed man in the overall classification, named after the red light shown on trains to mark the rearmost carriage. In a race where just finishing is a considerable achievement even being last is still an honour.

Team: There are 20 teams. After every stage, the times of the first three riders across the line from each team are added up and counted. The team with the lowest aggregate time in Paris wins the award.

You bet they do. The Tour de France is an individual event in thesense that every man pushes his own pedals to get around the course.But champions like Armstrong are quick to pay tribute to their supportriders.

Team members who are not in the frame for major awards- or "domestiques" - do the donkey work that enables their leader tothrive, or sometimes simply to survive.

This may mean fetchingand carrying water and supplies from the team car. It may meanproviding a small slipstream (not permitted in an individual timetrial) by spending a lot of time at the front of the peloton. Or itcould even mean handing over their bike to allow their team leader tocontinue riding while they wait for a replacement.

A contender stripped of all of his team-mates in a breakaway or a mountain climb is very vulnerable.

Just a bit. Many experts rate it the toughest of all major sportingevents and participants burn up to 10,000 calories per day in theirpursuit of glory.

But for the determined club cyclist, training for and riding a Tour de France stage is the thing of sporting dreams.

Failing that though, simply watch "le grand" spectacle from your own livingroom. Or from the streets of France. And prepare to be amazed.

http://news.bbc.co.uk/sport2/hi/other_sports/cycling/8129490.stm