Its worth noting that knobbies fling water slightly differently than a slick tire because the knobs prevent the water from running to the midline of the tire. I don't ride on the road much with MTB tires, but I've noticed they fling water in a more scattered pattern, but haven't paid much attention to the specifics. The tread could effect the angle that water is actually flung from the tire, but thats just a hypothesis.

For sure, you get more spray in the face with knobbed tires. Road tires are a death trap in the snow and ice, however. Here's my rainy day setup:
http://farm4.static.flickr.com/3230/...42c4891e_b.jpg

I agree that the side spray from the front wheel is probably not a problem for the drive train, and that much (but not all) of the centrifugal spray off the front wheel that might otherwise hit the chain, is probably contained by a full front fender. A little bit might fly back from below the fender and get on the chain rings. So a front fender offers some protection to the drive train.

For the rear wheel, it's possible that some of the side spray rises steeply enough to reach the lower chain run, and no fender will help here. So the question boils down to what happens to the centrifugal spray off the rear wheel? Will the fender in some cases act like a half pipe and divert some of that centrifugal spray right back back down parallel to the wheel and onto the rear derailleur? You say no, I say maybe.

Water shooting out the side of the fender (halfpipe style)is unlikely with a regular arched fender unless there was really a lot of water being forecefully flung onto the fender (see disclaimer below). Normally, if the tire and fender and correctly aligned, the high-velocity tire spray should initially be flung toward the midline of the fender. Once that happens, water can do three things. (1) It can fall back into the tire and be sprayed up again, (2) it can run to the front or back end of the fender and harmlessly drip off, (3) or it can drip off the sides of the fender onto the hub, derailleur etc.

Above, the claim was made that this side runoff (#3) is potentially worse for the cassette, hub and RD than simply going fenderless. I was thinking about this riding home today and I noticed my fenders (planet bike) have a lip running along the sides of the fender that prevents this. The lip acts as a gutter. Water running to the edge of the fender is diverted by the lip and runs toward the front or back end of the fender. I don't know if other fenders have the same lip, but it seems that well-designed fenders would have such a lip. It certainly works....at least, in the thousands of miles of wet road riding with planet bike fenders I have never seen water spraying or dripping from the sides of the fenders down onto the hub, cassette, or derailleur, nor have I ever seen any evidence of it in the form of dirty residues on said components. However, whenever the roads are wet, water is always conspicuously dripping off the ends of the fenders, which tells me the fender is doing its job correctly. Its possible other fenders don't work as well, either because they lack the lip or they generate less surface tension.

Note: A clip-on "backscratcher" will not work this way. Water will simply drip off of it...it is meant to protect you and not the bike.

(Disclaimer): In a torential downpour with flooded roads, all bets are off of course.. The amount of water being kicked up by the tires exceeds the ability of the fenders to divert water. At any rate, with or without fenders, you're bike is going to be exposed to road water in severe rain.

oh no, time to get a full chainguard

Holy thread resurrection Batman! and to the day, uncanny!

novara headwind pants. they're snug but not tight like lycra. I wouldn't wear jeans under them though.

http://www.rei.com/product/815145/no...ike-pants-mens

over jeans you can wear thin rain pants