This front guard from CycraGuard has ladder straps that make it easy to get a good ﬁt on a large range of different down tubes, from monster carbon ones to skinnier steel, and even square ones.
Running down the centre is a soft rubber section that widens and squares out at the top, so you can push the guard up close to the fork crown, which stops lots of muck getting through.
Two rubber plugs are provided which pop in easily and hold the guard slightly off the surface of the down tube. Combined with grooves down each side, this makes the CycraGuard workable for bikes with down tube cable routing.
Unlike bigger (and heavier) motocross-style guards that track the fork, these down tube-mounted fenders can only do so much, but they do keep most of the mud out of your face.
NOTE: Price is for front and rear mudguard set. You can read a review of the rear guard here.