According to used car buying guide parkers extra weight can reduce a car s mpg by up to 20 per cent because the engine has to work harder to haul it around.
Roof box impact on fuel economy.
Roof boxes too are designed to be wind cheating so at low speed their impact on economy is negligible.
Their study was published recently in the.
The control test the tourx without roof rails installed revealed that adding roof rails alone decreased the car s fuel economy by about seven percent or a negative 2 mpg change.
Not all down to the box some would be due to four people in the car and the boot full as well.
But the higher the speed the more affect they have.
The roof rack mpg experiment he compared the gas mileage of his car at 54 7 mph 88 kph with 1 no roof racks 2 an empty roof rack and 3 a mountain bike on the roof rack.
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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.
Rear mount cargo boxes or trays reduce fuel economy by much less only 1 or 2 in city driving and 1 to 5 on the highway.
All my thule stuff was one of my best purchases in a while browsed cl and got all my stuff for about 150 bucks would have been 350 400 new.
They found that in 2015 roof racks nationwide were responsible for 0 8 percent of light duty vehicle fuel consumption or 100 million gallons of gasoline.
Check the instructions about maximum speed mine states 60mph max it has seen 90 but i did get nervous.
My jetta wagon goes from 29 5with nothing on the roof to 27 5 with a box.
But no matter how aerodynamic it might look it also alters the flow of air around your carefully shaped wind tunnel tested.
Adding any roof box increases frontal area of your vehicle of course.
Adding a roof box means your car has to carve a bigger hole in the air which requires burning more fuel so your mpg will suffer.
It s impossible to give an exact figure because it depends on so many factors but britain s biggest roof box manufacturer thule states that your mpg is unlikely to decrease by more than 5.
Mileage went from 41 mpg at 65 mph to 40 mpg.
