Originally Posted by ArmyofOne
The reason your single rear wheel is rated to tow more than a dually is simple really. It fly's in the face of logic until you really think about it.
Picture your SRW with 2k on it, the tire is bubbled a little right? What happens when you apply turning force (TQ) to the wheel? It creates friction. Bu adding a second rear wheel to each side, you INCREASE friction, and therefore resistance. That resistance is what makes a difference in your towing capacity. All other things being equal, it comes down to, your SRW isnt turning 4 tires with a crapload of weight on them, it only has to turn 2. The reason's why many people run dually's eludes me, in most cases it is not nessecary. The only time you REALLY need a dually, is if most/all of your weight is centered over the axle, for the stability. Anyone who has hauled around a bed camper in a SRW and then hauled a camper in a DRW will tell you its night and day. It might feel better towing with a DRW, but when towing, DRW can actually hurt, not help.
You are way overthinking this, the SRW can pull more because it weights LESS, the difference in towing capacity is weight of the dual rear wheels with all else being equal. in that case something other than the wheels & tires are the limiting factor. one of my previous truck was a 3/4 ton ram and was the same way, it could pull MORE that the 3500 dually but couldn't carry as much. the only difference between the 2 were the dual wheels. it is true that there is more friction with 2 additional tires BUT it will NEVER be enough to make a SRW be better towing than a dually! the stability of a dually is better ALL the time! my current truck is a dually and I can also tell you it is more stable even empty that my SRW was. the only time the duals are a disadvantage is due to sheer size and expense replacing tires!