'Pulling' on a climb is far different than pulling a relatively flat section. On the climb, you are pacing as much as pulling, and have to keep the pace at whatever is doable for the person you are helping. It's comparatively easy to hang onto a line on the flats, where wind resistance is paramount; not so true on a hard climb, where gravity is king. When they are in the lead on a climb, Europcar is trying to set a pace that is just barely manageable for TV, and not one bit faster. This is why, every now and then, you will someone's domestique open up a gap, then look around, and you can almost hear them say "wups"; then they back off. They set a pace their leader couldn't match.