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.
Roof box impact on fuel economy.
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.
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.
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.
But no matter how aerodynamic it might look it also alters the flow of air around your carefully shaped wind tunnel tested.
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.
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.
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.
Aug 2 2010 3 20pm 0 0.
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.
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 the higher the speed the more affect they have.
Adding any roof box increases frontal area of your vehicle of course.
Roof boxes too are designed to be wind cheating so at low speed their impact on economy is negligible.
A large blunt roof top cargo box for example can reduce fuel economy by around 2 to 8 in city driving 6 to 17 on the highway and 10 to 25 at interstate speeds 65 mph to 75 mph.
Mileage went from 41 mpg at 65 mph to 40 mpg.
Roof box and fuel economy ijws15 used to lose about 4 5 mpg in the 1 8 t saloon.
