Bicycle hitch affect on efficiency x

[Slowflight]

I recently installed a Stealth hitch on my M3P to transport my bicycle. I was interested to find that the energy efficiency dropped from 270 Wh/Mi to 320 Wh/Mi over the same route. Max speed 60mph

 

[Foxsbiscuits]

Yea it's the aerodynamics/drag. You've basically put a metal wall with holes on the back of your car .
I assume that's why people mount them on the roof?
Also how are you getting 270 this time of year? I'm M3LR averaging about 330Wh in the cold.

 

[Slowflight]

Living in Florida certainly improves HV battery efficiency

 

[Slowflight]

But it would be interesting to see the change in efficiency between roof mounted bicycles and hitch mounted bikes. Notwithstanding Foxbiscuits’ remarks (and they are substantially correct!), a roof mounted bike is in a localized area of higher pressure which increases drag, whereas a hitch mounted bike is in a localized area of lower pressure which, though more turbulent, should lower total drag. I certainly can’t predict the outcome, but it would be interesting if some curious soul out there could test it

 

[Foxsbiscuits]

I think you're right actually, from my very basic internet research the roof rack option is less aero.
Maybe rerun your route test? Sometimes wind can play a big factor.
I don't see how adding the bike could lower drag but I'm no physicist, would be good to hear others opinions with accompanying data.

 

[Kevy Baby]

There's something fishy about a efficiency drop that significant over JUST the addition of the bike rack.

Unless in addition to the rack (and presumably bikes), you also had a ton of cargo in the car. Oh, and it was a really cold and windy day. And...