I just came back from five week trip to Austin, Texas (Mpls to Austin). I was hauling two pets, another passenger, two bikes (on back rack) and luggage. I was SHOCKED to see how drastic my milelage changed throughout the trip. It varied by tank anywhere from 40 MPGs, down to 25 MPG. It did seem quite windy, but couldn't believe the MPG could drop this low! I was doing freeway driving and also noticed that I never got any recharge icons on the display screen. When I was driving in Austin, my average MPG was nearly 50mpg throughout the hills in Austin, so it didn't seem to be a hill thing. Wondering if it was either freeway driving (no stopping, starting), wind or hauling load. Any ideas? Thanks!
Wind, I had the same problem coming up from Brownsville to Corpus Christi, wind cut down mileage really bad.
The bikes increased your Cd and your frontal surface area. At freeway speeds, that increased aero drag is very significant, making the engine work harder. You didn't mention what speeds you ran, but you should have seen impg vary with speed...
wallymw, If you took the bikes off while driving in Austin, getting the "regular," 50 MPG is a clear indication of the massive negative effect of the bikes in the rack on your MPGs. I'm not so sure of increased frontal area, but the airflow in the supercritical area at the back of the car was most likely all screwed up = increased drag = low MPGs.. It comes with the territory whether its a bike rack, roof rack, windows open, whatever. The Prius' FE is very sensitive to increased Cd at speeds probably as low as 20 MPH.
Not long ago, Consumer Reports had a small segment talking about cargo on top, tire pressure, etc. That cargo on top decreased MPG by about 10, if I remember correctly. So, depending on your cargo on top, it could be even more. Just having the hardware on top can have a measured effect.
