Originally Posted by trackhead
Why are people paying money to put mud clogging, low clearance fenders on dirt bikes? It seems counter intuitive.
As mentioned before, less rock thru radiator risk yes, but perhaps the main reason is cooling ... you lose up to 50% of your effective cooling with the airflow blocked by by a high fender (most rally bikes have a large single radiator going all the way across)... the fender covers a third of your radiator surface area, and adds so much turbulence to the remaining airflow hitting your radiator that it significantly reduces cooling on the remaining 2/3 of your radiator.
Additionally, in rallys these bikes spend a fair bit of time around 75 - 100 mph ... and the low fender is significantly more aerodynamically stable and efficient than a high fender. At those speeds its a significant difference.
So in answer to your question, there are 3 good reasons to use low fenders on dirt bikes, and only 1 reason not to.
Even when it is muddy (light mud) a low fender is better at keeping mud spray off your headlight and goggles as well.
As rallys tend to be held on fast dirt gravel roads, sand etc, there are plenty of reasons to use a low fender.
This is how much cooling you can get with a low fender:
And this is how much gets cut off with a high fender:
And this is what can happen with your high fender cause you dont get enough cooling: