If you're planning on strapping a kayak to the roof of your car and hitting the open road, there are a few things you need to keep in mind. First and foremost, you'll need to make sure your kayak is properly secured. The last thing you want is for it to come flying off the roof while you're driving! Once it's secure, though, there are no hard and fast rules about how fast you can drive with a kayak on the roof.
Of course, common sense dictates that you shouldn't push the limits too much. If you're driving at high speeds or in windy conditions, it's best to play it safe and slow down. In general, though, as long as your kayak is securely attached to the roof of your car, you should be able to drive at normal speeds without any problems.
So there you have it - there's no need to worry about how fast you can drive with a kayak on the roof. Just make sure it's properly secured and use common sense when making decisions about speed and weather conditions.