How bad is this, Aerodynamically? (rear-mounted bike rack on SUV)

[skyking]

Pulling one wheel and moving over should get most of your loss back, as suggested above. At some point it should be inside a "bubble" that will form in any case. That is the "money" bubble we try to eliminate

[KamperBob]

A 1-2mpg loss with a bike on back isn't much. Go ahead and remove the front wheel, turn handlebars flat and recenter as suggested it can't hurt. But don't expect to get back to baseline. The bubble behind your tailgate isn't static. A pair of eddy currents rotate in 3D with mirror symmetry down the vertical center plane of the vehicle. Balance dictates forward flow up the center then outwards towards each side. A smooth tailgate facilitates that flow bubble. A bike impedes that flow. Satisfaction follows expectations.

[pete c]

I have had a new Kia Rio for the last week. Most of my hiway driving up to this point has returned mid thirties mpg. Today I drove to Burlington, VT. Brought the wife and both our mountainbikes on the trunk mounted rack. It absolutely killed my mileage. I saw about 26 mpg. I could definitely feel it. Like I was dragging a parachute.

I would guess that the SUV wasn't hurt as badly as the roofline is high all the way back, so the bike is tucked down in the wake. Not so a fairly aero sedan.

I could have done as well bringing the wife's Odyssey with the bikes inside!

[freebeard]

Are you sure? 1-2mpg on 30? How much raw data collected in what way?

It could be head/tail winds or even barometric pressure.

Without the bike is without the rack as well? Adding a diverter below the back bumper might do as much or more than the 'spoiler'.