How Much Fuel Does a Roof Rack Waste?
Calculate the exact additional fuel, financial cost, and extra drag coefficient (Cd) caused by carrying a roof box, rack, or bicycle.
Trip & Vehicle Parameters
*Note: Aerodynamic drag increases exponentially with speed squared (Fd ∝ v²).
Your Streamlined Roof Box adds +0.085 Cd to aerodynamic drag, burning an extra 3.2 gal of fuel over 250 miles.
Removing your roof attachment when not actively carrying cargo saves hundreds of dollars annually in unnecessary aerodynamic air drag.
Why Does a Roof Rack Waste So Much Fuel?
At highway speeds (65+ mph / 105+ km/h), over 60% of engine power goes purely into pushing through air resistance.
Empty Crossbars at 65 MPH
Carrying empty roof rack crossbars alone degrades fuel economy by 11% on sedans and 8% on SUVs.
Roof Box at 80 MPH (130 km/h)
A roof cargo box increases fuel consumption by up to 2.0 Liters per 100 km (approx +22% higher fuel usage).
Roof-Mounted Bicycles
Two bicycles mounted on the roof created the largest aerodynamic drag spike, reducing overall range by 31%.
FAQ
Yes, even empty roof bars noticeably reduce fuel economy. Carrying bare crossbars alone increases aerodynamic drag and degrades fuel economy by 8% to 11% at highway speeds (65+ mph). Over 12,000 miles of driving, an empty roof rack can waste $150 to $280 in unnecessary fuel costs.
Yes, a hard-shell roof box is significantly more fuel-efficient. Hard-shell cargo boxes are engineered with streamlined aerodynamic profiles (adding roughly +18% drag), whereas non-aerodynamic soft cargo bags catch much more wind and can increase aerodynamic drag by up to +35%, resulting in nearly double the extra fuel consumption.
Removing a roof rack when not in use can save you between $150 and $300+ per year in gas. For long highway trips or yearly commutes, removing empty bars, cargo boxes, or roof bike mounts reduces aerodynamic drag back to your vehicle's factory efficiency baseline.