If Froome really wanted to he could limit Nibs to less than a minute, even with Nibs riding full out and a thunderstorm. To be honest I think people overestimate the gains Nibali can gain over Froome on descents.
Maybe Froome won't wanna risk chasing though, but that's just because Nibali is 8 minutes back.
Maybe Froome won't wanna risk chasing though, but that's just because Nibali is 8 minutes back.