The Alpe d'Huez

I'm not doing this just to start an argument, but what makes it so difficult, it's a pretty constant slope, so you find a gear that lets you spin at a required amount, stick it on, and off you go.

Errr. It's not a constant slope. The bottom 6 k is average 9%, kicking up past 10% in places, the middle 4 is a little less steep, and from the last hairpin to the village is just mad, mad steep. As is the first 2k to the first hairpin. So steep, you could fall down it walking!

I did it a few times, and only really felt on top of the gear when I was running 39 X 32. Admittedly, I have only ever done it at the end of the Marmotte or after riding from the Vercors, and up through Grenoble.