Whatever roof carrying system you have, whether you wish to mount a roofbox, cycle carriers, surf board or ski carriers you will need to mount it on a set of roof bars. It is therefore worth considering the humble roof bar in more detail.
The Thule brand is well established and the market leader in roof racks and related equipment. They have a reputation for being expensive, which they can be, but by keeping to the lower end of their product range and shopping online I have found prices competitive with, for example, Halfords own brand. There are many online retailers but roofracks.co.uk and towequipe.co.uk are two that I have used a number of times and can recommend.
Within the Thule range there are two basic designs of roof bar: the Aero bar made of aluminium, which is light and aerodynamic but around twice the price of the alternative Square bar, which is made from steel. The Square bar has the further advantage of being practically universal: almost any brand of roof carrying accessory can be mounted onto it without the need for an adapter or special fittings. Since I did not expect to travel at high speeds for long distances the aerodynamic efficiency of the Aero bars was not significant and I chose the cheaper Square bar.
The pairs come boxed as a pair and are available in several different lengths to suit a wide range of cars. The Thule site has a configurator that allows you to select the correct roof bars and foot pack for your car. The foot pack is what you need to mount the bars onto your car. Different packs are needed for cars with roof rails to those without. While you can mount foot packs almost anywhere along the length of a roof rail, if you need to use the type that clamp directly to the car's roof, usually fitting in the door openings, there will be specific points, often marked on the car, where the feet must be fitted. Your car handbook should explain this in more detail.
A third possibility is that your car has mounting points in the roof itself, usually identified by having a thick trim strip running the length of the roof a little inboard from the door openings on each side. The mounting points are normally concealed under covers that need to be prised off. I have seen this arrangement on Renault Scénics, for example. If you have a pre 1990 car that has rain gutters then I don't think you will be able use any of the Thule foot packs, unless the car also has roof rails.
A final consideration is whether to go for a standard or low profile foot pack. The low profile is more aerodynamic and will save an inch or so in height but brings the roof rails closer to the roof line, potentially creating difficulties if you need to reach under the roof rail to secure a fitting above it. I decided to go for a standard profile foot pack.
The bars themselves are painted black with a ridged plastic covering on the top. The underneath is slotted to allow the feet to be fitted on each side when a plastic cover clips over the open end of the roof bar. This assembly is simple, requires no tools and is explained clearly in Thule's instruction leaflet. In my case I then simply placed the open part of the feet over the roof rails, clamped them up by hand and locked them in place with the integral lock in each foot.
As far as spacing goes it is important to observe the minimum spacing of 700 mm between the front and rear roof bar as well as see that they are centred correctly with an equal overlap each side of the roof rails. Thule advise that wind noise from the bars will be reduced if they are placed further to the rear of the car. The combined weight of the roof bars and footpack is 6 kg and total weight allowed -including this - is 100 kg. Of course, you should also observe the weight limit for your car, which may be lower.
In use I have not been unduly trouble by wind noise. Sometimes I have heard a low moaning sound but this seems to depend on the weather at the time. The bars have stood up to a season's regular use and after being cleaned were in excellent condition with no corrosion or deterioration of the painted finish. However, I did notice some dents in the plastic coating where cycle carriers had been left in place for some time, which I think is acceptable.
Facts and figures at a glance
~Weight: (with footpack) 6kg
~Usable load limit: 94kg maximum
~Speed limit: - depends on load or accessories fitted
Price is variable of course but you will usually get a better deal by buying together with the footpack, which you will need anyway.
Roof bars will adversely affect fuel consumption, particularly at higher speeds. It is therefore a good idea to remove them when they are not needed.
As part of the Thule range they have been City Crash tested, road tested and subjected to a Sleeping Policeman test. I find all that reassuring.