Do not use thule load carriers and accessories for purposes other than those for which they were designed.
Speed limit with roof box.
My usual trip to south of france is 36 38 mpg with roof box 32 34.
Aerodynamic drag increases with speed and exceeding the speed rating could effectively exert too much force onto the accessory or the roof rack.
Some roof boxes are rated for a maximum of 60 mph so check this out before you buy.
Their car has a roof rack and it seems to you that the items attached to it are wobbling as.
Do not exceed their carrying capacity.
The only statement that thule has on the speed you should travel while carrying a cargo box on the roof like th615 is the following.
Max speed when driving with a roof box.
Adapt your speed to the conditions of the road and the load being carried.
Bars that have an aerofoil shape are the quietest.
As long as your rack is properly attached to the roof and you re not exceeding the weight limits how can there be.
A lot of roof rack accessories such as roof boxes come with maximum speed ratings.
For safety to your vehicle and rack system obey all posted speed limits and traffic cautions.
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Adapt your speed to the conditions of the road and the load being carried.
With a well designed roof box and roof bars wind noise shouldn t be much of a problem.
Exceeding the speed rating could damage your car or the roof rack.
There s just one difference.
There shouldn t be any maximum speed.
As far as you can see the driver in front is also doing everything they should to stay safe on the roads.
Wind noise and fuel economy.
If towing a caravan you re already limited therefore no problem but solo it might be.
You re driving well within the speed limit and keeping a two second gap between your vehicle and the car in front.
You ll introduce a hell of a lot of drag and significantly lower gas mileage but otherwise there should be no problems at any speed.
The speed rating more than like has to do with drag and lift factors as mentioned above.
Some roof rack accessories such as roof boxes come with a maximum speed warning which shouldn t be exceeded.