While I agree that roof-mount carriers have an FE penalty (even beyond best design) they are generally small in both volume and weight capacity. Importantly, they are centered over the vehicle,
between the FF/RR axles. The weight is hopefully not enough to affect COG meaningfully.
Whereas the hitch carriers may not have quite the capacity, they
tend to exceed the TW (trailer Tongue Weight) capacity all too often as I have seen whilst running the roads. This is a safety concern: unloads the front axle which is a seriously bad idea for braking/steering control. Changes other handling qualities of the vehicle (
polar moment of inertia) which is even worse in some situations.
I'd rather have a small trailer. The U-Haul "Sport Trailer" weighs 540-lbs, with a capacity of 39 c/f and a cargo weight of up to 965-lbs (TTW 1,500-lbs).
Aero doesn't begin to describe this trailer.
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