This depends on your car. Every car’s roof has a different weight rating, and you should find your specific car’s rating. One thing to note, is that the roof rack counts as weight, too. So if your roof is rated to carry up to 180 lbs, but your roof rack weighs 35 lbs itself, you’re only left with 155 lbs leftover. It’s also important to note that these are driving weights, and your roof can hold much heavier loads when stationary, like when you’ll actually be using the tent.