Done it a couple of times, my tips:
1) You can’t be too fit. If you were to go out on a fast,hot, very hilly 100 miler, how would you feel? La Marmotte is this, getting hotter as they day goes on, and you hit the Alpe with humidity at a high level. Build your miles up to regular 100 mile plus rides, with mates and really push on the climbs.
2) You can’t be too light. That’s you and your lardy arse! Ok, that’s me really, but if you work on item 1), 2) will surely follow. Unless your a world champion pie eater. I’m your size, it’s not much benefit!
3) Your bike must fit you. Spending all day riding up proper mountains in building heat and humidity will find out any issues. A super super light bike, Assos shorts and electronic gearshift couldn’t matter less. There will be a very dark skinned pensioner riding past, smiling, wearing a woolen top on a bike he bought as a teenager. Clever marketing won’t make you faster, but a bike that fits will keep you riding comfortably for longer.
4) Go down the week before and practice a few climbs and descents. The Glandon at speed is fearsome. They don’t advertise it but several people have died on its slopes. The roads can have a very poor surface and watch out for melting tarmac patches. A buzz, certainly, but it’s nice to know where the road goes. The first descent can be (has been) carnage.
5) Start slow, enjoy it. Look at the view, chat to your fellow riders. If it’s your first time and you’re not chasing gold take some pics. Remember you’re doing it for for fun.
6) Try and avoid taking the front in the peleton on the valley roads, sit at the back and spin!
7) Have a drinking and eating strategy. There are many water fountains and pumps away from feeding stations that will get you filled up more efficiently. Take some nice sarnies wrapped in foil. Endless energy food is tiresome,have some nice nosh for a pick me up.
Eight) THE MOST IMPORTANT BIT – the route can vary, but:
The Glandon is a long climb. It’ll probably be cool and seem quite easy. You’ll wonder what all the fuss was about. Go steady on the descent. Cruise the valley.
The Telegraphe is a nice climb, enjoy.
The Galibier gets progressively tougher. After Plan Lachat it turns back on itself and gets steep and unrelenting. The descent of the the Lauteret is a main road with traffic and tunnels. Some lit, some not. One rider I saw ended up in intensive care crashing in a tunnel…
SAVE SOMETHING FOR THE ALPE. It’s steep, the first three ramps will set the tone nicely, and it’ll probably be very humid at that time of day. You’ll have 99 mountain miles in your legs by the time you start it…
Enjoy! I shall be going again. It’s a truly epic day out.