With rain in the forecast for the weekend, I was looking into some mud riding tips, and found Dave Carr's Mud Index. I hope we don't see it this weekend, but here goes:
Dave Carr's Mud Index
Mud is ranked on a scale of 0 to 10, zero being hard dry dirt and 10 being liquid water. Other properties include material content, color, stickiness, and so on.
Grade 0 - Dirt, and all facsimiles thereof like adobe, clay, hardpack, dust, rock and pavement. Fails to give your bike and body that virtuous muddy look that lets people know you're a cyclocross god. Not really relevant to a discussion of Mud.
Grade 1 - Damp Earth. Nice and soft, tacky. Makes a pleasant sound as tires roll over it. Fun and effortless to ride on. Ultimate traction. Never separates from the ground, or if it does it doesn't stick to the bike. Your bike could be so clean after a ride that friends think you never went out.
Grade 2 - Adobe Clay. A bad kind of damp earth, found in certain regions of the US. Soft and sticky enough that it sticks to shoes, but doesn't separate from the ground very easily. Slows down the bike and drains a rider's energy without apparent cause. Low moisture content. Fills the pedal cleats on the shoes, rendering them heavy and useless. Following a rain, this type quickly transforms into Grade 3.
Grade 3 - Play-Doh. Water content is up to about 20-30%, leading to major sticking action. Literally jumps from the earth to your bike. Accretes to the tires, filling the treads. Fills up the tight spots between the tire and frame tubes, and in between the cassette cogs. Causes the bike to gain ten pounds in a matter of minutes. Requires pressure sprayer and brush to remove.
Grade 4 - Peanut Butter. Less sticky than Play-doh; more likely to stay on the ground. Moisture content is up to 40% or so. This stuff is sticky enough that one can't really plow through it, yet it's slippery and makes it hard to control the bike. Ruts form which may yield to a tire, or send the bike careening off in an unanticipated direction. Requires ferocious pedaling to keep momentum. Occasionally a piece sticks to the tire and is thrown into the air; subsequently lands on another rider's face.
Grade 5 - Goo. About as thick and sticky as the energy gel you eat during a race, only brown and slightly less tasty, and more likely to be lumpy. Like Peanut Butter, Goo stays on the ground, but is less resistant to the advancing tire. At East Bay CX races this type often includes some content of cow dung or rotting flesh. In more pleasant venues Goo may be found on the verge of a wet grassy area where a few tires have passed.
Grade 6 - Slime. This is the level of mud where a rider really begins to have fun. Slime is wet enough that it sticks to everything but doesn't really build up on the bike. Sticks together well enough that it will fly through the air in large masses. This grade is used in TV commercials for four-wheel drive trucks, in which the truck slides around all over the place shucking mud in every direction. In a 'cross race, Slime often is found in corners where it can wreak havoc with traction, leading to a slide on your butt on the wet ground.
Grade 7 - Glop. This is the wettest consistency of mud that can still hold a shape. When tires pass through Glop, a furrow is left that heals up slowly over time to a smooth surface. Liquid water may come to the top. It's better to have thin 'cross tires to slice through this stuff, while fat MTB tires will float and plow and generally make a mess. Imparts a shiny appearance to bicycle and body parts.
Grade 8 - Slop. The bottom of a very wet mud puddle that is not refreshed by a creek. Still retains some lumpy qualities, unlike Grade 9 Soup. Splatters very nicely and stains clothing better than any other type. Renders your glasses completely opaque. Remember not to smile at your friends after a dunk in this stuff unless you want them to laugh hysterically at the mud between your teeth. Requires a good hose-off to clean, plus a few cycles in the laundry.
Grade 9 - Soup. 80-90% water, heavily laden with sand, particulate and goo, but without the lumps characteristic of Slop. Scientists might classify this grade as a "Non-Newtonian Fluid." Typical of a stream crossing where the stream flow isn't fast enough to refresh the mud. Will soak your jersey completely, while leaving the particulate matter all over the front. Doesn't stick to the bike, instead just runs off onto the ground.
Grade 10 - River Water. Might feature some residual brown color but doesn't stick to anything. Just wet and cold without any redeeming qualities other than it may loosen up thicker grades of mud from your tires and shoes.
Stolen from here . There are also some nice pics of that various grades of mud.