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the fearsome Mont du Chat
Checked out the profile of that yesterday... looks horrible. For some reason last time I was down there I did the Vercors rather than the Chartreuse massif but it could have just been I wanted to ride the balcony roads coming down from Col du Mont-Noir (stunning but the descent is a bit dicey in places if there are cars coming up).
Might do a loop from Chanaz up to Grand Colombier though and around the lake.
atz-
Yes, the Mont du Chat can be grim, especially if it's warm as it's so low you don't get that cooling effect you get at higher altitudes.
I like the Vercors, some great roads to ride there but it can get busy. For some reason the Chartreuse is quieter, despite being between the Aix-les-Bains/Chambery and Grenoble conurbations.
andyp
The Chartreuse massif is worth a visit - some great climbs, stunning scenery and it's usually pretty quiet too.
The ridge west of the Lac du Bourget has some great climbs, including the fearsome Mont du Chat, probably one of the hardest and most underrated climbs in that part of France.
At the north end of the lake is the Grand Colombier which is always worth a visit by bike. Plenty of options up and down, but some are tough.
I've not ridden there myself, but friends toured the area south west of Lyon, out to St Etienne and beyond a few years back and enjoyed the riding a lot.