Does a Roof Rack Use Enough Extra Gas That You Should Remove It?

Aerodynamic drag is one of the forces resisting a vehicle as it moves through the air. A roof rack adds objects and surfaces above the main body of the vehicle, disturbing airflow and increasing drag.

The engine then has to produce additional power to maintain the same road speed. At low speeds, rolling resistance and other losses can be relatively more important. As speed rises, aerodynamic drag becomes increasingly significant.

Adding a roof rack increases the aerodynamic work required to maintain speed. That extra work ultimately appears as additional energy or fuel consumption.

Published testing demonstrates why blanket claims about a specific percentage are misleading. Different vehicles, rack shapes, crossbar positions, cargo loads, and test speeds produce different results.

Because the range is so wide, the calculator intentionally asks you to enter an assumed penalty and shows what that assumption means financially. It does not pretend to measure your vehicle.

Aerodynamic drag increases rapidly as vehicle speed rises. That means an aerodynamic accessory can have a relatively small effect during low-speed urban driving but a much larger effect during sustained highway travel.

This is why your annual highway miles are more informative than your total mileage when estimating the practical cost of leaving an aerodynamic accessory installed.

A roof rack does not exist in isolation. The body's shape, roofline, windshield angle, height, width, existing roof rails, and other aerodynamic features all influence the resulting airflow.

The practical consequence is that a fuel-economy result from one vehicle should not automatically be applied to another.

The simplest roof configuration is a set of crossbars with nothing mounted to them. Adding equipment increases the amount of air the vehicle has to move around.

Not every visible roof component should be treated as something the owner can or should remove. Factory roof rails may be integrated into the vehicle's design, while aftermarket crossbars and accessories are often removable.

Only remove equipment the manufacturer or accessory instructions indicate is intended to be removable. Never modify structural or safety-related vehicle components simply to chase a small fuel savings.

Suppose removing your rack improved fuel economy by a modest amount. That does not automatically mean you should remove it every time. There is a time and convenience cost to taking it down, storing it, and reinstalling it.

Your useful comparison is therefore:

The calculator gives you the annual and multi-year fuel cost so you can make that comparison using your own driving rather than someone else's MPG test.

An EV still has to overcome aerodynamic drag. Instead of measuring the penalty in gallons of gasoline, you experience it through additional electricity consumption and reduced driving range.

The same physical questions still apply: vehicle shape, speed, rack configuration, and cargo all influence the amount of aerodynamic resistance.

If you want to estimate the actual penalty for your own vehicle, you can compare fuel economy with and without the rack under as similar conditions as practical.

A controlled test is especially valuable when the cost difference is small and you want to know whether removing the rack is worth the inconvenience for your particular vehicle.