There are 21 stages in the Tour de France and every single one of them counts, but for different reasons to different riders. There are sprint stages in the first and second weeks that will be pivotal in the green jersey battle. And, of course, there is the final stage on the Champs-Elysees, which is always special. But here are five stages that we believe will be key to winning the maillot jaune this year.

1. Stage 8: Castres to Ax 3 Domaines, 195km

This is the first high mountain stage and the first summit finish of the Tour. Unlike many of the previous years’ Tours, the first week isn’t all about the flats – there are two medium mountain stages from the beginning and a few rolling stages that will require concentration and some legs. This eighth straight day of racing starts out innocuously enough, leaving the climbing until the last 50km or so of the stage. And what climbing it will be! The boys go straight into the first HC mountain, the Col de Pailheres, which rises to 2,001 metres (the highest point in this year’s Tour).

Stage 8 profile

At an average 8% gradient, there’s no gentle start to the climb, which means anyone out of sorts will suffer. The Sky train will want to be fully functioning and keeping any attackers at bay, but they might not be able to. First over the summit has a fast 20km descent before heading straight into the final climb, Ax 3 Domaines. There’s no time to catch your breath if you’re in front, no time to regroup and rethink if you’re off the pace – it’s 8km of climbing at over 8% to the summit and every one of those will see an attack.

2. Stage 15: Givors to Mont Ventoux, 242.5km

The most unforgiving climb of the Tour this year: Mont Ventoux. Like stage eight, most of the day is tempo riding – there are a few cat 3s and 4s but everyone will be saving it for the summit finish. The guys start the climb 22km from the finish – and it will be pure hell. The first half of the mountain has the steepest inclines – 11 unrelentless kilometres of nothing less than 9%. When the forest ends, it’s nothing but a stifling hot lunar landscape until the summit – usually with a headwind. Whoever wins will be a Tour legend. Any GC contender who falls behind could lose a lot of minutes and his chance of the podium.

Stage 18: Gap to Alpe d’Huez, 168.5km

They say the Tour is won on the Alpe – we’ll see if that’s true here.

With both time trials done and dusted, any podium hopeful who has good climbing legs and time to make up will be on the attack and this could very well be the deciding stage of the Tour. There are six climbs, two of which are Alpe d’Huez. The first pass comes 120km into the stage, but it’s not necessarily the ascent that’s going to sort the men from the boys but the descent – very narrow, very steep and very technical. There is no margin for error. They come back around and climb the 21 hairpins again for a spectacular mountain finish. If Alberto Contador needs to make up time, expect him to attack on every inch of this mountain.

Stage 19: Bourg-d’Oisans to Le Grand-Bornand, 204.5km

Stage 19 profile

Five big climbs that start immediately. The first half of this stage contains two monster HC climbs, the second half has three tricky climbs before a short, fast descent into Le Grand Bornand. This may not be a summit finish but it will blow the peloton apart. The first two climbs have what used to be Andy Schleck written all over them – will he make a Galibier-like statement? Will the GC contenders risk it after their gruelling double-Alpe day and the equally gruelling test to come the following day? The guys who are sitting in the podium positions might want to reserve something for Saturday but they can’t be complacent as the also-rans could use this stage to try to sneak away.

5. Stage 20: Annecy to Annecy-Semnoz, 125km

Stage 20 profile

Six climbs spread throughout this short 125km stage, including a summit finish on the HC climb to Semnoz. The final 11km of climbing in this year’s Tour has an average gradient of 8.5% but starts out steep and narrow. Could someone get caught out and lose a podium place? If the maillot jaune is still up for grabs, the last part of this stage could rival the fireworks planned for the finale on the Champs-Elysees. If it isn’t, this could be the day we see what a new young climber has to offer the cycling world. Either way, it’ll be glorious.