Yes. Roof racks and roof boxes can reduce a REEV’s electric range and increase petrol consumption when the range extender is supplying energy. They add weight and aerodynamic drag, with the effect generally becoming more noticeable at motorway speeds.
A roof box can still be useful when the boot is full. You just need to account for the extra energy use and check the vehicle’s load limits before packing.
Why Does a Roof Box Affect Range?
Equipment on the roof changes how air flows around the vehicle. The electric motors must use more energy to overcome that resistance, particularly at higher speeds. Additional weight also increases the energy needed to accelerate and climb hills.
Research from the US Department of Energy confirms that roof cargo can have a greater efficiency penalty at higher speeds. An empty box still creates drag, so leaving it fitted between trips can affect consumption too.
In a REEV, this means the battery’s stored energy may cover fewer kilometres. When the range extender generates electricity, the additional demand can also increase petrol use.
How Much Range Will You Lose?
There is no single percentage that applies to every vehicle. The result depends on:
- Equipment: Bare crossbars, a roof box and an open basket affect airflow differently.
- Speed and wind: Faster driving and headwinds increase aerodynamic resistance.
- Load: The weight and shape of what you carry influence consumption.
Figures measured on another SUV should not be treated as a prediction for your iCAUR. Leave extra margin in your charging and fuel plans, and monitor average consumption during the journey.
For other factors that affect the estimate, read why your REEV’s driving range changes from day to day.
Check the Roof Load Before Packing
The roof-load limit includes the rack, mounting equipment, box and luggage.
For example, a 75 kg driving roof-load limit, minus 25 kg of carrying equipment, leaves 50 kg for luggage, provided the rack and box also permit it. These are illustrative figures, not iCAUR specifications.
Check the limits and approved fitment for your exact model. A higher-capacity rack does not increase the vehicle’s permitted roof load. Rooftop tents require a separate compatibility check, including the supported load when parked and occupied.
How to Keep the Impact Down
- Use the boot first. Keep heavier items low and secured inside; use the box for bulky, lighter belongings.
- Drive at a steady, appropriate speed. Follow the equipment’s speed restrictions as well as road limits.
- Check total height. Measure the vehicle with the box fitted before entering covered parking.
- Secure everything correctly. Follow the fitting instructions and recheck the fixings as directed.
- Remove unused equipment. An empty roof box still affects airflow.
A roof box gives you useful extra space, but expect higher consumption while it is fitted. Choose compatible equipment, stay within the load limits and allow a little more range for the journey.
