Roof top carrier vs trailer hitch cargo rack? Effect on mileage

[DrivingForce]

Going on a 300 mile round trip beach trip with the family and need a solution to increase cargo. Roof top box seems simplest, but I'm afraid it could decrease my range on the highway substantially. Anybody have any idea if a trailer hitch unit is better for this?

[IanL]

I think that a trailer (unless it was very streamlined) would create more wind resistance than a nicely faired roof box.

[DrivingForce]

Ah, sorry I meant a trailer hitch-mounted cargo box that sits behind the rear bumper, not a trailer. That way the frontal area of the car isn't changed.

I've noticed my Soul is extremely susceptible to head winds when it comes to range reduction. A roof top box might cause a similar situation.

[IanL]

Ah, sorry I meant a trailer hitch-mounted cargo box that sits behind the rear bumper, not a trailer. That way the frontal area of the car isn't changed.

Its not just an issue of the frontal area. A protrusion at the rear may create a fair amount of turbulence in the airflow, which causes drag. Ask a C130 pilot what having the ramp down to the horizontal does to his airspeed and how much he has to open the throttles to compensate.

[DrivingForce]

Ah, sorry I meant a trailer hitch-mounted cargo box that sits behind the rear bumper, not a trailer. That way the frontal area of the car isn't changed.

Its not just an issue of the frontal area. A protrusion at the rear may create a fair amount of turbulence in the airflow, which causes drag. Ask a C130 pilot what having the ramp down to the horizontal does to his airspeed and how much he has to open the throttles to compensate.

This is true, but I think the area behind the Soul is a very turbulent area anyway since it is not a streamlined car. A rooftop box will also mess up the flow of air. Arguably even more than a trailer hitch mounted cargo box.

I guess nobody has tried both?

I'd try the hitch method, but I can't seem to find good info on a trailer hitch that works, and also I would need some sort of license plate bracket since the license plate would be blocked.

[notfred]

Here's a thread about adding a trailer hitch to the Soul EV viewtopic.php?p=12542

[jray3]

I guarantee the difference will be noticeably better with a hitch-mounted cargo carrier than a rooftop box. Main downside is further reduction of our tenuous FWD Traction in hill-climbing…. I ran back-to back tests with my RWD I-MiEV a decade ago, and then stuck with the hitch rather than roof whenever possible.