Don't know how wide the factory flaps are, but as long as they are at least as wide as the pair of tires, they should be OK. I doubt if the flaps will protect much against water and dirt, but the main thing is to protect against throwing up rocks and pebbles, which come mainly out of the tread. It seems to me that flaps wider than the tires would just get in your way. JMHO
2003 Ford F-350 V-10 Crew Cab 4WD Long Bed
2004 Jayco Designer Medallion 29 RLTS 5th wheel
Bill, Gayle, and Mindi (dachshund)
Retired at last !
Nothing is foolproof to a sufficiently talented fool.