For safety to your vehicle and rack system obey all posted speed limits and traffic cautions.
Speed limit with roof box.
The speed rating more than like has to do with drag and lift factors as mentioned above.
With reference to the amount of petrol used the consumption will go up whatever speed you go at with a roofbox on so going slower is not going to improve consumption it s all relative the ideal speed for consumption is around 55 60 but that does not mean you have to increase your speed to this to get ideal consumption if in a 30 or 40 limit as it does not mean you should reduce from 70 to this to significantly increase performance.
With a well designed roof box and roof bars wind noise shouldn t be much of a problem.
A lot of roof rack accessories such as roof boxes come with maximum speed ratings.
Max speed when driving with a roof box.
For safety to your vehicle and rack system obey all posted speed limits and traffic cautions.
Do not use thule load carriers and accessories for purposes other than those for which they were designed.
Adapt your speed to the conditions of the road and the load being carried.
Some roof boxes are rated for a maximum of 60 mph so check this out before you buy.
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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.
Bars that have an aerofoil shape are the quietest.
If towing a caravan you re already limited therefore no problem but solo it might be.
There s just one difference.
Exceeding the speed rating could damage your car or the roof rack.
Their car has a roof rack and it seems to you that the items attached to it are wobbling as.
Adapt your speed to the conditions of the road and the load being carried.
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.
Do not exceed their carrying capacity.
You re driving well within the speed limit and keeping a two second gap between your vehicle and the car in front.
There shouldn t be any maximum speed.
Be sure to read their instructions carefully too.
As long as your rack is properly attached to the roof and you re not exceeding the weight limits how can there be.
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.