Route highlights and main contenders of the Tour de France 2018

Twenty-one stages, 26 tough climbs across six mountain ranges, three mountain-top finishes and two time trials will test the limits of 176 riders' endurance and skill in the Tour de France, which begins Saturday in the Vendee area along the Atlantic coast.

Here is a quick look at what the peloton can expect in the 105th edition of cycling's greatest race, a three-week marathon over a route covering 3,351 kilometers (2,082 miles):

OFF WITH A SPLASH

Two flat stages should provide a fast-paced start as sprinters battle it out for a chance to wear the race leader's iconic yellow jersey - a highlight in any rider's career.

Starting on the island of Noirmoutier-en-l'Ile, Stage 1 is a 201kilometer introduction with gentle gradients to welcome 22 teams of eight riders to the race, and Stage 2 provides another early opportunity to shine.

This is great for spectators as riders will hold nothing back as they fight for the lead before one of the favorites can take over, increasing the likelihood of crashes that can damage top contenders' chances.

TINKERING WITH TIME

To spice up the start even more, carrots of 3, 2 and 1 bonus seconds will be offered to the first three riders to reach a specific kilometer determined in advance over the first nine stages.

More conventional time bonuses of 10, 6 and 4 seconds will be taken off the overall times of the top three in each normal stage of the race (excluding time-trials).

All of the bonuses may result in more changes in race leadership.

Stage 3 is a 35.5-kilometer team time trial in Cholet that could see riders on weaker teams drop behind in the overall standings.

The only individual time trial comes in the penultimate stage and should settle the overall places before the riders point their bikes in the direction of the Champs-Elysees' cobblestones for the largely ceremonial final stage in Paris on July 29.

HOBBLED BY COBBLES

Most riders hate cobblestones and Stage 9 on July 15 will be sure to test their bonhomie with 15 cobbled paths scattered along 21.7 kilometers of the 156.5-kilometer course from Arras to Roubaix, beside the Belgian border.

While exciting for spectators, the bumpy ride will be a nightmare for many competitors, particularly if the weather is wet or windy. Falls are likely and this stage could end some riders' hopes of an overall victory.

MOUNTAIN MIGHT

The surviving riders are going to need their rest day in Annecy on July 16 before the Tour heads to the Alps for the first of three testing stages that could reshuffle the standings. All three legs in the Alps feature daunting climbs and frightening descents, culminating in the awe-inspiring ascent up the 21 bends that lead to the famed 1,838-meter high Alpe d'Huez finish on July 19.

Almost half of the mountain climbs will be in the Alps (12), with four in the Massif central and 10 in the Pyrenees, where the Tour will pass through Spain for a brief 15 kilometers. Otherwise, this year's Tour is exclusively French.

QUEEN QUAKER

This year's so-called "queen stage" - the stage that stands out for its difficulty and race drama appears to be the 200.5-kilometer mountain leg from Lourdes to Laruns in the Pyrenees on July 27.

It will provide "a last opportunity for riders to change the general classification," according to race director Christian Prudhomme.

The route takes in the 1,490meter Col d'Aspin, 2,115-meter Col du Tourmalet and 1,709-meter Col d'Aubisque, with a steep descent to Laruns providing a challenging finish for riders still competing for the yellow jersey.

The main contenders

CHRIS FROOME Age: 33 Froome is the undisputed favorite to triumph for a recordtying fifth time after being cleared of doping by the International Cycling Union on Monday.

The Kenyan-born British rider is aiming to join the elite group of Jacques Anquetil, Eddy Merckx, Bernard Hinault and Miguel Indurain as the only cyclists who have won cycling's biggest race five times.

Froome enters the three-week trek on the best winning run of his career.

After his dominant performance to win a fourth Tour last summer, Froome won both the Spanish Vuelta in September and Giro d'Italia in May.

That made him only the third rider to hold all three Grand Tour titles at the same time and the first to achieve the feat since the Vuelta was moved to the end of the season in 1995.

Main assets: Confidence and experience of a proven champion, skills for the high mountains and time trials, and strong support from Team Sky.

Question marks: How is Froome's stamina holding up after his crash-marred Giro victory and the doping case, which led to months of debate?

Age: 28 A winner of the Vuelta and the Giro, Quintana has planned his season around winning the elusive Tour.

The Colombian scaled back his competition schedule this year and did not compete in the Giro to give him fresher legs at the Tour after he finished a disappointing 12th last year, his worst showing in his five entries in the race.

Quintana twice finished runnerup behind Froome in 2013 and 2015.

He is aiming to become just the eighth rider ever to win all three Grand Tours.

Main assets: An elite climber, on-par with Froome when at his best, he will be backed by a very strong Movistar team that includes Mikel Landa and veteran Alejandro Valverde.

Questions marks: Can he build a big enough lead before the individual time trial in the penultimate stage, given his weakness in races against the clock compared to Froome and other rivals? Or if he falters early, will Movistar shift its hopes to Landa or Valverde?

Age: 27 Dumoulin won the 2016 Giro and finished second behind Froome in the Italian race this year.

The Dutch rider won two stages of the 2016 Tour, and came agonizingly close to winning the Vuelta in 2015.

Main assets: A powerful rider who excels in time trials as well as rugged terrain.

Questions marks: Although he has improved in the mountains, will he be able to challenge Froome and the other world-class climbers when it matters? Will he get enough help from Team Sunweb to hang with powerhouses Sky and Movistar? Age: 33 The only man to win the Tour besides Froome over the past five years, Nibali is also the only other former champion to ride this year.

He joins Froome in that exclusive group of riders who have won the Tour, Vuelta and Giro in their careers.

The Italian won the Milano-San Remo classic in March but skipped the Giro to prepare for what could be his last realistic opportunity to repeat his 2014 Tour win.

Main assets: A champion's pedigree on every kind of terrain, proven climbing credentials and excellent downhill skills.

Question marks: Does he still have the strength to topple Froome? Can his Bahrain-Merida team give him the support he will surely need?

Age: 27 France's hopes to end a 33-yearlong wait for a homegrown Tour champion rest on Bardet.

He has finished on the podium for the last two Tours and won stages in the race in each of the last three editions.

Main assets: Climbing skills and attacking attitude.

Question marks: Can he improve in the individual time trial after struggling last year? And how well will Bardet and his AG2R La Mondiale team hold up on the first team time trial at the Tour after a three-year absence?