I get the same thing on long, hot rides. I did try Chamois Butt'r on the area once, and it didn't prevent it from occurring. Just like for everyone else, it doesn't happen on short or cooler rides. Maybe we should take up a collection and one of us can go to a dermatologist and get a name for whatever it is? In the past, I have gotten exercise-induced urticaria, but an antihistamine pre-ride prevents it. I don't get EIU on road bike rides, even without an antihistamine. I will get it on my arms when mountain biking and on my legs when running. Weird.

Alex