# Best Roof Boxes for Electric Cars: How Much Range Do You Lose? By EV Charge Cables · Published 3 November 2026 **The short version** A roof box adds aerodynamic drag that costs range on an EV more than on a petrol car. A 500L box at 70mph typically reduces range by 15–25%. The key is choosing a box with a low drag coefficient and keeping motorway speed down. For shorter runs, the range penalty is manageable. - Hard shell boxes have lower drag than soft bags — choose hard shell for motorway trips - Speed matters more than the box: at 60mph the penalty is roughly half what it is at 70mph - Soft bags (no roof rack needed) are fine for city/slow roads where drag is minimal Roof boxes and EVs are not natural companions. A petrol car loses some fuel efficiency; an EV loses measurable range — and range anxiety makes that feel worse. But the penalty is predictable and manageable if you choose the right box and adjust your speed expectations. Here is what to know before buying. ### How much range does a roof box actually cost? Aerodynamic drag increases with the square of speed. At motorway speeds (70mph), a large roof box can add 15–25% range loss compared to driving without it. At 60mph, the penalty roughly halves. In town at 30mph, it is barely measurable. The drag coefficient of the box matters more than its size alone. A long, narrow, aerofoil-shaped box like the Thule Motion XT creates less drag than a short, boxy one at the same volume. For EV owners doing long motorway runs, box shape and keeping speed to 60mph are the two most effective levers. | Scenario | Speed | Approx. range penalty | | --- | --- | --- | | Hard shell aerofoil box, 420L | 60mph | 10–13% | | Hard shell aerofoil box, 420L | 70mph | 18–22% | | Soft cargo bag, 400L | 60mph | 12–15% | | Soft cargo bag, 400L | 70mph | 22–28% | | No roof box | Any | 0% | If you are doing 200 miles of motorway with a 300-mile range EV and a roof box at 70mph, plan for an extra stop. At 60mph on the same car, you likely make it without a stop or with one quick top-up. ### Hard shell vs soft bag: which is better for EVs? For motorway trips in an EV, a hard shell box is the better choice. Hard shell aerofoil designs have a lower drag coefficient than soft bags, which tend to billow and create turbulence. The difference matters most above 60mph. Soft bags (also called cargo carriers) attach with straps and do not require a roof rack. They are cheaper, easy to store, and fine for low-speed trips: going to a campsite via A-roads, moving house locally, or carrying kit to a day event. If your journey is mainly motorway, spend the extra on a hard shell. ### Do I need a roof rack? Hard shell roof boxes require a roof rack (also called roof bars). Most EVs have fixing points for aftermarket roof bars; check your car's handbook or a fitting guide. Soft bags attach with straps directly to the roof and frame — no rack needed. If you already have roof bars from a previous car, check the width and load rating before fitting a box. ### Our picks #### Best hard shell for motorway EV trips: COSTWAY 400L The COSTWAY 400L is a decent mid-range hard shell that fits most roof rack systems. At around £250, it is a fraction of Thule pricing without sacrificing the key benefit of a rigid aerofoil shape. Dual-side opening makes loading easier when parked parallel to a wall or fence. **pick: COSTWAY 400L Hard Shell Roof Box** - 400L capacity - Dual-side opening - Fits most roof rack systems - Lockable - Low profile aerofoil shape Price: £254.95. [Buy on Amazon](https://www.amazon.co.uk/dp/B0BSRY95RT/ref=nosim?tag=evchargecable-21) #### Best budget: Amazon Basics rooftop cargo bag If you are doing a one-off move or a slow-road trip and do not want to spend £250 on a hard shell, a soft cargo bag is the pragmatic choice. No roof rack needed, folds flat for storage, and waterproof for UK weather. Just keep your speed down. **budget: Amazon Basics Rooftop Cargo Carrier Bag 425L** - 425L capacity - No roof rack needed - Waterproof heavy duty material - 8 straps for secure fixing - Folds flat for storage Price: £43.99. [Buy on Amazon](https://www.amazon.co.uk/dp/B072ZHRDMZ/ref=nosim?tag=evchargecable-21) #### Flexible soft bag: Rooftop Cargo Carrier This reinforced cargo bag sits between a cheap supermarket bag and a full hard shell in both price and protection. Suitable for camping gear, sleeping bags, and bulky items you want to keep separate from the boot. **pick: Rooftop Cargo Carrier Bag 1000D** - Heavy duty 1000D material - 100% waterproof - Universal straps - Folds into carry bag - Multiple sizes available Price: £48.88. [Buy on Amazon](https://www.amazon.co.uk/dp/B0BFWQJ7LP/ref=nosim?tag=evchargecable-21) ### Tips for using a roof box on an EV - Drive at 60mph instead of 70mph — the range saving is significant and the time cost is usually 10–15 minutes on a two-hour journey - Remove the box when not in use — even an empty box adds drag - If you have a range estimator, check it after 5–10 miles with the box fitted to calibrate your actual loss - Load heavier items low in the boot rather than the box — EV range is also sensitive to total weight - Pre-condition the car before setting off on cold days so you are not using heater power on top of box drag --- Canonical version: https://www.evchargecable.co.uk/blogs/guides/best-roof-boxes-for-electric-cars EV Charge Cables, EV charging cables matched to your car: https://www.evchargecable.co.uk. Some links in this article are Amazon affiliate links; as an Amazon Associate we earn from qualifying purchases at no extra cost to you.