Last week I went to the Smokey Mountains Nation State park in Tennessee, and on Wednesday I decided to ride the park roads, it began to sprinkle so I put on my $12 rain jacket and my helmet cover and started riding, before long it was downpouring and very windy. I rode in that for 20 miles, only my hands, face, legs and feet got wet and cold, but almost a week after the ride I still haven't caught a cold.
The weird part of that ride was this one section I got on called the Loop, and it had two sections warning bikers to get off and walk their bikes because it was too steep down...what? I rode down steeper grades than either of those two in California and never dismounted the bike! So I rode the bike down those grades in the rain and didn't have any issues...other than the rain and wind, but those two didn't cause me to crash and burn.