He found that compared to the baseline of no roof rack the empty rack reduced his mpg by 12 7 and the roof rack with a bicycle reduced it by a whooping 27 3.
Roof rack gas mileage impact.
Mileage went from 41 mpg at 65 mph to 40 mpg.
This means that adding an empty roof rack to a car that usually gets 35 mpg will drop the gas mileage to 32 5 mpg.
A drop of 7 percent may not sound like much but it adds up over time.
A close second was the kayak with 28 percent or a change.
Adding an empty roof rack to a vehicle can drop the gas mileage by about 7 percent.
The gear with the most impact were the dual mountain bikes strapped to the roof which impacted the fuel economy by 31 percent or 9 mpg.
This editor many years ago in a move across the country to oregon from michigan found that the highway mileage of a four cylinder accord dropped from more than 40 mpg down to 32 mpg with a.
The empty roof rack had a nearly 2 percent impact on fuel economy which translates to a little more than three quarters of a gallon of gas.
I ll justify these numbers below.
An empty rack has been reported to increase the cost of fuel over time from anywhere from 1 to 15 while a fully loaded roof rack will add 20 to 50 to your fuel bill.
The other great thing with the thule system is that it takes literally 2 minutes to get the box off and maybe 5 10 mins to take the bars off each time so it really isnt that much of a hastle if you want to save on gas when you re not using it.
Unfortunately even an empty roof rack will affect mileage.
Mileage went from 41 mpg at 65 mph to 40 mpg.
Their study was published recently in the journal energy policy in a paper titled fuel consumption impacts of auto roof racks.