OK, so you don't have to pedal, power-to-weight ratio is really not an issue and it doesn't feel like every sinew in your body is about to splutter into uselessness. But it's an art nonetheless and takes a huge amount of dexterity, hand strength for the all-important braking and, above all, a flagrant disregard for what could happen.
Doesn't feel like much in a car on the open road, but hurtling down a mountainside at 40+ miles an hour on a bike along tightly bending roads is good enough for any speed-junkie.
So there you are. Blasting along the greatest descent in Europe surrounded by the stunning Savoie countryside. And you're looking at 100 yards of tarmac ahead of you the whole time. Knowing that a puncture or one lapse in concentration could see you rag-dolling along the road or careering off over the edge into the abyss. It's a situation where vision and line of sight is everything.
Hold that thought. Is it in there? Good.
Now imagine you're gunning it at more than 40 miles an hour along that twisty, turny road when, all of a sudden, someone turns out the lights and you're cycling blind. It's at this point the road gets rough and you need both hands on the bars to keep it upright. The buzz-saw of a million car exhausts is ringing in your ears. At odd intervals, you can just make out the whites of sad-eyed monsters creeping inexorably your way in a game of what is, for you anyway, suicidal chicken.
Welcome to my world in the tunnel before La Grave. I had been warned about it, but even my hopefully nightmarish description above doesn't do it justice. I have genuinely never been more scared on a bike than in the first few moments of the tunnel. There was no lighting to speak of, save a row of smogged-up bulbs overhead that were giving out about as much of a beam as a fading tea-light. I was doing a silly speed and the road began to bobble, so both hands were gripping the bars firmly, which probably didn't help.
Neither, I admit, did the sunglasses I was wearing, but I had no opportunity to remove them, so there they remained. A virtual blindfold I was unable to shed. I couldn't see the lines down the centre of the road. I couldn't see where the tunnel wall was. God knows what would have happened if the road had deviated from the gun-barrel straight. What seemed like years later, a dim light appeared at the end of the tunnel and I pedalled hard for it, hoping above hope it wasn't the light of an oncoming juggernaut.
Coming out of the tunnel was like being born again. I had been given life and it was precious. And I aimed to keep hold of it for a bit longer, so I pulled over and removed the offending sunglasses in preparation for the next few tunnels, which thankfully weren't as long.
Once through them, the road smoothed out and became a joy to ride on. It perhaps would have been even better without the freak, torrential 15-minute downpour that summoned up the road grease like a blackbird tapping up the morning worm.
A quick comfort break and banana stop at the bottom of the descent gave me the chance to stretch my legs and wait for Martin, which didn't take long. We hacked our way further along the valley past a glorious looking dammed lake and on towards Bourg d'Oisans, taking turns in a good, swift group that boosted our progress.
Up until we were stymied by my chain coming off after a routine gear change. Thanks, Shimano. No, really.
But it was all downhill to the bottom of the Alpe from there along nice, smooth roads. So determined was I to reach the timing mat before the cut-off point that I shouldered most of the burden of the headwind on the front of a long line of riders. But I felt strong enough to tow the rest and, as I'd been helped out earlier in the day, it seemed only fair.
The stop in Bourg d'Oisans was confusing, with plenty of people strewn around clearly going nowhere. Could they really be stopping now with just one more climb to go? Our water bottles filled, we made our way over the timing mat and pulled over out of the now searing heat in the shade afforded by a small hedge. Here, we topped up on gels and fruit bars in readiness for the final assault...