The ascent starts in the valley of Bourg d'Oisans (700 m approximately) via the same road that takes us to the Col du Lautaret (D1091) through Lake Chambon at just over 1000 m in altitude. Start cycling uphill in the first part, the most difficult section (gradient greater than 10%) of the Alpe d'Huez hill.
In the village of La Garde you will need to change course, to leave behind (almost) all other traffic of any kind. Head towards the Route de l’Armentier which, after the short berm to La Garde, goes uphill at a sustained but manageable gradient. The road takes us to an altitude of about 1350 m and offers a superb view over the region (and a view of the Col de Solude opposite).
The descent that follows takes you to Le Freney d'Oisans at just over 900 m above sea level and joins the Route du Barrage du Chambon (Chambon Dam road) below. At the lake, to reach the Col de Sarenne (now distant 13 km away at an average gradient of 7.5% with a 1045 m change in altitude of which 6.5 km are at 8.9%), take the road that climbs sharply to the village of Mizoen.
This is where the road has a berm and even a short descent at the exit from the village before continuing to climb at high gradients. The arrival at Le Perron via a narrow road in excellent condition marks a change, for it is from this village that you begin the last kilometres of the route, in a wild landscape and a steep winding road with several passages of more than 10%.
The pass may be quite crowded with hikers in the summer. At the top, there is only one hiking sign to indicate the altitude but no sign marking the road pass. There is also a refuge, the Sarenne refuge.