Forget the Velominati: the one real rule in mountain biking is that if the weather’s going to change, it’s always going to do it when you’re at the highest and most exposed section of your whole ride.
You’ll be hot and sweaty from the climb, and as ready as you’re ever going to be for five minutes’ rest, a cereal bar and a good chew of the cud with your riding buddies. Then, just as you finally catch your breath, wipe the sweat from your eyes and start drinking in those hard-earned views, the heavens will open.