I recommend 2 1/2 inch ducting to the front bumper. You'll have to squeeze the ducting around the air pump but it still works fine.

 

i have been thinking. i was planning on putting 2.5" ducts and have placed a 2.5" inlet on the dust shield of my AP2. since I have a bunch of 2" ducts lying around. i just came to realize that i can probably squeeze 2 lines of 2" from the bumper ( the holes are long vertically but narrow horizontally) to about where the shocks are. then, place a dual 2" to 2.5" collector with a 90 degree of exit so the 2.5" duct is a straight shot to the rotors. this will introduce less fatigue on the ducts since the bends are handled by the collector and also prevent rubbing with 255 tires since stacking 2 2" ducts on top of each other is narrower than just 1 2.5". in terms of air pressure, a larger surface area inlet at the bumper reducing to a 2.5" outlet at the rotor will result in higher pressure than if the hose was just 1 constant diameter the whole way through.

what do you guys think?