How will a roof rack affect your car? Roof racks, loads and towing in the theory test

Updated 25 October 2026•6 min read

A roof rack or roof box makes your car use more fuel, so take it off when you are not using it. The DVSA's car driving syllabus says learners should understand how roof top boxes can increase fuel consumption, and should remove roof racks when they are not needed.

That is the answer theory test questions about roof racks are looking for. The rest of this page covers the other rules about carrying a load or towing, because questions on this topic often ask about handling, tyre pressures and speed limits too. Every rule below comes from gov.uk, and we checked each page on 25 October 2026.

Why a roof rack increases fuel consumption

The DVSA publishes a free learning to drive a car syllabus, which sets out what a learner needs to know. Its unit on driving safely and efficiently lists two points about roof racks:

removing excess weight, including roof racks or storage, from your vehicle when not needed
how carrying unnecessary equipment or luggage, such as roof top boxes, can increase fuel consumption

A roof box also adds to the effect of speed. A 2011 Department for Transport notice on saving money on holiday driving says that at motorway speeds a roof box can increase fuel consumption by around 25%. It advises keeping your speed down when you use one, and suggests taking the box off at your destination if you are not going to use it.

So if a question asks how a roof rack will affect your car, the answer is that it will use more fuel. The same unit of the syllabus covers the other fuel-saving habits that come up in the test, such as planning ahead so you can brake smoothly and thinking about air conditioning. Our eco-safe driving guide goes through them all.

Loads and how your car handles

A roof rack or cycle carrier is a way of carrying a load, and loads have their own rules. The syllabus unit on preparing a vehicle and its occupants for a journey says a driver should understand:

the types of load securing equipment, such as roof racks and cycle carriers, and when to use them
that you must not allow any load to stick out dangerously from your vehicle
that passengers or loads can affect handling when cornering, accelerating and braking
that older vehicles may be more affected by loads than newer vehicles with stability control
how to use the vehicle handbook to find the adjustments to make, such as tyre pressures
that a load may restrict your view, so you need to take active steps to see as much as you can

In short, a loaded car takes longer to stop, leans more in bends and may need higher tyre pressures. The handbook for your car gives the figures. For the tyre rules themselves, see our guide to tyres and vehicle safety checks.

What Highway Code rule 98 says

Highway Code rule 98 covers towing and loading. For loads, it says:

you must not overload your vehicle or trailer
you must secure your load, and it must not stick out dangerously
heavy or sharp objects and any animals should be secured, because in a collision they could hit someone inside the vehicle and cause serious injury
carrying a load or pulling a trailer may mean you need to adjust your headlights

"Must" in the Highway Code means the rule is the law. Our Highway Code guide explains the difference between "must" and "should", which matters in theory test answers.

If you tow a trailer or caravan

Rule 98 also covers towing, and gov.uk's towing with a car page sets out what your licence allows.

Rule	What gov.uk says
What you can tow	If you got your licence from 1 January 1997, you can tow a trailer up to 3,500kg maximum authorised mass.
Before you tow	Your car and trailer must be roadworthy, including legal tyres, working trailer brakes and working trailer lights (rule 98).
Loading a trailer	Spread the weight evenly, with heavy items over the axles, to reduce the chance of snaking (rule 98).
Mirrors	If the trailer or load is wider than your car or blocks your view behind, you must use towing mirrors (rule 98).
If it snakes	Ease off the accelerator and slow down gently. Do not brake harshly (rule 98).
Speed and lanes	Lower speed limits apply, your stopping distance may increase a lot, and you must not use the right-hand lane of a motorway with three or more lanes (rule 98).

For the towing speed limits on each type of road, see our UK speed limits guide. For how a heavier vehicle changes your stopping distance, see stopping distances. Driving anything heavier than a car and trailer needs a different licence and theory test: see which theory test covers motorbikes, lorries and instructors.

How these questions are asked

Questions on this topic tend to be short. You might be asked how a roof rack affects your car, what to do with a roof box you are not using, how a heavy load changes your tyre pressures, or what to do if a caravan starts to snake. If you know the reason behind each rule (drag and weight use fuel, loads change handling, a loose load is dangerous in a crash), you can answer however the question is worded.

theorytest.ai is independent and is not affiliated with the DVSA. The rules above come from gov.uk, so check there if you are revising some time after the date at the top of this page.

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