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Roof box tips: which to buy, how to fit it, reducing noise and storage solutions

Here's our guide to all things 'roof box'!

Mercedes-Benz roof box

Mercedes-Benz roof box

So you want a bit more space without having to fork out for a new car? A roof box is a great option. However, we know that it’s a minefield out there. Not only is there a huge range of roof boxes to choose from, but you also need to consider various other accessories, and other factors such as storing your roof box when it’s not in use and even fitting the thing in the first place!

It’s a lot to take in. But don’t worry, we’ve got you covered, and have devised this how-to article to help you through the various different stages when buying a roof box. So bear with us, and we’ll take it from the start…

Check your car manual

First thing’s first; check your car user manual for the maximum load capacity your car can hold on its roof. It may seem obvious, but often people don’t consider that certain cars can carry more weight than others, and this should be the first factor in your mind when shopping for a box.

Size and shape

Now you know the maximum capacity that your car can hold on its roof, you can start to consider the size and shape of roof box that would best suit your vehicle and needs.

There are various shapes of roof boxes you can buy, but generally speaking, they stem from two main types; rounded and square/rectangular. A rounded roof box is good for use as a ‘second boot space’ – perfect for extra equipment and clothing, but nothing too big. For those of you with extra items such as a pram or ski poles, you might want to consider a square box, as this would allow more space for bulky gear.

In terms of width, narrow boxes are really handy if you want to leave space for a bike or two, or even a kayak. These can come in long or shorter sizes, so it really depends what your ratio of box gear is to larger additional items such as bikes.

A wider box is good for families, although it limits what else you can fit on the roof. A wide box may still allow room for a bike or two if it is short enough, or if you use aero bars (don’t worry, we’ll get to that soon!) When using a wider box, always put the bikes on a rear bike mount off the boot.

Boxes that are both long and wide are excellent for families, as they can fit the most gear in. However they are big and cumbersome, and can be tricky to move.

Another top tip: consider the conditions you will be driving in. For the skiers among you – choose wisely. Buying cheap may not be the best idea, as weaker roof boxes can crack in cold weather due to being made of brittle plastic.

Base system

So now you’ve picked the best size and shape for your roof box, we can move onto the next step in the shopping process. This part is extremely important. Unfortunately it’s not as easy as choosing a box and sticking it on top of your car; there are a few more accessories you need first.

While older cars had rain gutters built in that made it easy to attach your roof rack, more modern cars don’t and many even have a completely flat roof, which makes the process a little trickier.

A complete roof rack system includes a fit kit, towers, and cross bars. The cross bars carry all your stuff, the towers grab the cross bars and the fit kit clips it all to your roof. Lets start from the beginning:

  • Fit kit – This is necessary if you have a flush roof, with no built in gutters or factory roof rack installed. These kits consist of clips called feet or connectors that attach to the corners of your roof to accommodate the bars. This is the only item that is specific to your vehicle, so check which clips you need before buying. (Image: Fit kit in bold, attached to towers, which hold the cross bars.)

  • Towers – It is very important that the towers are fitted properly to your car, as you don’t want all your gear flying off down the motorway without you! The good thing about these, though, is that they are universal, so if you change your car, you will just need to get a new set of fit clips to reattach your rack.

  • Cross bars – Cross bars hold everything together. There are three main types: square, circular or aero. Square bars are the cheapest, although they are the least aerodynamic, meaning more whistling at high speeds and a higher mpg. Thule’s aero bars are undoubtedly the best option, but alas, they are also the most expensive. Factors that make them stand out are the increased fuel economy and the fact they are quieter, and look better. Sitting in between these two are the circular options, which provide a happy medium if you can’t afford to go aero. Sliding bars are also available, which make getting to the box easier, especially on wide or tall vehicles.

If this all sounds a bit confusing, Thule’s ‘Fit Guide’ lets you choose your vehicle and shows you roof racks and boxes that are compatible with your car.


These are what attach your roof box to your base system. There are two main types of connectors: U-bolts and T Track adaptors.

  • U-bolts – These usually come as standard with most roof boxes. They are suitable for all roof boxes, however there are some downsides to using the U-bolts. If you decided to opt for the aero bar, you cannot use U-bolts to attach your roof box. U-bolts can also scratch softer aluminium bars.

  • T Track adaptors – These look a lot sleeker when fitted, and can also be used with aero cross bars. T Track adaptors spread the load and cut down on wind noise.


Once you’re happy with your purchases, you can start to consider fitting your roof rack and box to your vehicle.

All Arnold Clark dealerships can source and fit roof boxes for you, so if you are uncomfortable with fitting your own box, don’t hesitate to contact your local dealer for more information.

The ease with which you can fit your roof box depends on what size and shape you opted for. A long-wide box for example, could take two people to lift onto the vehicle.

How to stop whistling noise coming from your roof rack and box

One of the main annoyances for drivers with a roof box fitted is the whistling noise that occurs when travelling at high speeds. This whistling is caused by gaps between the bars and base. There are several things you can try to reduce this, which are as follows:

  • Reposition the rack – Move your cross bars around a little; move them forwards, backwards, even slant them slightly. This probably won’t fix the problem, but it could make it slightly more bearable.

  • Wrap rope around the bars – Wrap a bit of rope around the front cross bar, and wrap it around the length of the bars, tying it at the end to the other side of the cross bar. This is a bit of a DIY solution, but it does disrupt the airflow, therefore helping to reduce whistling.

  • Yakima “windjammer” airfoils – This handy little gadget snaps on the crossbar and creates a smooth flow of air to reduce wind noise. It’s also pretty cheap too!

  • Get a fairing – This is the most expensive solution, however it is also the most effective. The fairing works by increasing the streamlining of your vehicle, which reduces noise and also goes some way to increasing fuel economy by reducing drag.

As ever, you get what you pay for.

How to store your roof box

Roof boxes are handy things to have, but when you’re not using it, you may wish to take it off your car and store it elsewhere, either to increase fuel economy or perhaps because driving about looking like you’re going on holiday might not be so exciting on the commute to work!

Boxes are bulky items so the ideal place to store them is above your car in the garage, or perhaps in a shed. There are some fantastic solutions on the market specifically designed for roof boxes. These are:

  • Roof box hoist – This uses a pulley mechanism to hoist your box up from the roof of your car to the roof of your garage. It’s easy to use; you just unbolt your box from the cross bars and hoist it up!

  • Storage straps – These are a cheaper option, and work in a similar way in that they hold your roof box suspended from the roof of your shed or garage. They’re not quite so easy to use as the hoist, as they don’t use a pulley mechanism to lift the box up, however they work just as well.

Turn it upside down and use as a bath? … We’re joking of course, but owning a roof box when you don’t also have a garage can be a bit of a nuisance, as they are bulky items to carry up the stairs into the loft! They are quite weatherproof however, so if worst comes to worst, your roof box shouldn’t come to too much harm in the garden covered with some tarpaulin, although do bear thieves in mind!

That’s all from us. Hopefully we’ve covered all of your roof box questions, but if you have any more or wish to add any other solutions to help out fellow roof box owners, let us know on Twitter or Facebook.

About the Author

Sophie McGraw

Staff Writer at Arnold Clark