Originally Posted by
tjspiel
I mostly agree. Front fender must drop pretty low to keep spray off of your drivetrain. IME experience though, a seatpost mounted rear fender can be sufficient to keep the spray off of your back if it extends far enough rearward. It may not help the guy behind you at all however.
Yes, its actually pretty basic geometry. As long as the fender extends to the steepest imaginary line that intersects your backside and the very back of your rear wheel, it will basically protect you.