Riding gravel - mud...

Source: CXMagazine.com -- USA Cycling 2015 Nationals

Gravel + rain = mud.  Or not.
A lot depends on the geology, geography, and who maintains the road.  In parts of the country, gravel roads are no different wet or dry, except that a little more grit gets kicked up when it's wet.
in other regions, 'gravel' is just a code word for clay with a little native rock mixed in.  And trying to ride these is, well, interesting.  More like trying to ride road slicks on ice, covered in cooking oil, And then there's your average "B" road along the edge of Farmer Brown's bottom 40, where tractors dare not tread in the rainy season.  THAT is serious mud in any context.

Most promoters are going to avoid more than a short stretch of this stuff - at least if they want people to come back to their event again.  You can't always avoid it, and a little makes for great stories about epic struggles and adventures "There I was.  My shoe was at the bottom of a sucking hole, I'm up to my ass in the stuff, and Monica goes riding by like it's just no big deal..."  A lot makes for death marches, broken gear, and a plan to find something else to do that weekend next year.

So what do you do to survive the stuff?  Three tips -
PAM cooking spray on your bottom bracket, fork crown, pedals and other spots where mud typically clings.  This really will help keep it from building up quite as much, and will wash off pretty easily.
Good fenders (and PAM the undersides!).  Fenders will make your ride cleaner and drier, and make you much more popular with anyone riding behind you.
If you *know* there's going to be a lot of mud, go with a more aggressive open tread, like a Challenge Grifo.  The bigger blocks are slower, but shed mud much better.
The rest of it is experience. In order to be good at riding mud, you need to ride mud.  It's all about learning where to be, when you can ride the center between the puddles, and when you should ride through the slop.  It's quickly sizing up the mudhole and realizing that it's hub deep, sticky, and there's no way to ride it.  When that happens, look for the 'dry line' if it exists - the spots that look a little drier or less trampled, maybe a bit higher, or have a little grass to hold them together.  Or check for the wet line - where it may be a deeper hole, but it's wet sand instead of mud.  Or look for the sneak path through adjacent field.  Not that I condone tromping a farmer's crop, but maybe there's a line up on the grass verve that can be walked without being knee deep in the slime.

And don't forget to have a wash cloth, towel and a gallon of water in your car for cleaning up after the finish.  A quick wipe down, towel off and warm, dry clothes can really make the difference between a memorable day and a miserable one. And you can use any leftover water to sluice off the worst from your bike before you put it in/on the car.  An appropriate beverage and some good food help a lot as well.  Especially if you have those "So there I was..." stories to share!

Savor the mud - just in moderation!

~marsh