Originally Posted by
mdilthey
My Marmot Super-mica went unused when it rained on one of our biking days. Why, you ask?
Backpackers deal with this issue all the time. One of my comrades was a Long Trail/AT Veteran. When it began to rain and he saw me getting on my raincoat, he said "What are you doing? That's for camp."
Instead, I had my Merino Wool bike pants, my Under Armour t-shirt, and Merino Wool Arm Warmers from Smartwool. Water beaded up on the outside of the wool and eventually soaked in, but warmth was retained and 10 minutes after the rain stopped, I was completely dry. My best rain option has been to use my raincoat when my tent needs adjusting mid-storm, but for actual riding, merino wool is king.
I've used Smartwool for a while and I like it, but I find that it is fragile and develops holes, so I've gone over to synthetic long sleeve T-shirts. I use Techwick from EMS, but there are lots of similar products. It dries more quickly than Smartwool which is useful when you only have a couple of changes of clothes. If it rains on the bike I usually put on my Mica to keep me warm. Getting wet and then drying out while hiking is less of a concern than on a bike because your speed on the bike results in greater evaporative cooling that can quickly chill you. So I think it's best to put on something to keep you warm rather than dry. However, if I think it's going to be a quick downpour I just stop riding and look for some cover, or failing that, use my umbrella.