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Roof racks vs Fuel efficiency – The Facts

August 1, 2017

Roof racks vs Fuel efficiency
Our real-world tests show roof racks can ruin your mileage!

There seems to be a constant debate on how big an influence mounted roof racks, empty or loaded, have on your vehicle’s fuel economy.

Adding any rooftop carrier, cargo box, or bike rack doesn’t come free, and we’ve seen various reports with figures in the neighbourhood 15-50% added to the fuel use regardless of vehicle. In fact, our testing will show that it cuts your highway mileage all the time it’s installed, whether there’s luggage up there or not!

Audi Q5 Roof racks
Test Car – Audi Q5 with standard manufacturer’s roof racks installed.

So, to find out for ourselves, we took to the streets to do some real-world testing. Using an Audi Q5 2.0 TDi Manual as our test car, we did three separate test runs in three different rooftop configurations. The 25km test runs were conducted on an empty stretch of road on the N4 between Pretoria and eMalahleni. The environmental & road conditions were close to ideal, so take into account that extremely windy conditions, steep inclines & twisty roads etc. will negatively affect the fuel consumption even further.

Test Conditions
Test Distance (Per run) 25km
Test Speed 120km/h
Temperature 29 °C
Wind Conditions Mild (Almost no wind)
Road Surface Smooth
Road Incline Flat

 

Obviously, it’ll be different for every car and shape and size of roof rack, as well as contents of the rack, but herewith the findings of our simple experiment:

Test Car: 2010 Audi Q5 2.0 TDi (Manual)
No roof rack 8.3 l/100km
Empty roof rack (Standard Audi crossbars 2x – See picture) 9.1 l/100km (+9%)
Roof rack with Kayak (About 4,5m long) 10.2 l/100km (+22%)

Audi Q5 Roof racks
Audi Q5 – Standard cross-bar roof racks

Thus, the loaded roof rack increased fuel consumption by about 22% compared to the baseline. However, what is actually more surprising, is that the empty racks added a full 9% to the fuel consumption.

So, there you have it, driving around with empty roof racks on your car for a year could easily add in the region of R2000+ to your annual fuel expenses! (Taken at R10,9 / litre doing about 20k annually – will vary depending on the car you drive.)

Adding any protrusion will increase the drag area of your vehicle by altering the flow of air around your carefully shaped, wind-tunnel tested vehicle. The additional drag and turbulence could have a devastating effect on your fuel use.  Here are some additional fuel consumption additions that might surprise you:

Roof rack (Unloaded) Up to 18% (Full size rack)
Bull bar up to 14%
Snorkel up to 6%
Heavier tyres up to 25%

Note: These figures are calculated estimates only. All vehicles will show different fuel usage under different driving conditions.

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