From Clark Griswold in National Lampoon’s Vacation to your father lashing baggage to the family station wagon, generations of men have tried to stow too much luggage to the top of the family car. Hollywood and your hazy childhood memories are not far from reality, with many guys more likely to research bridge clearances on the way to the lake than running a quick Google search on car roof weight capacity. However, figuring out how much weight a car can carry ⏤ even if it fits nicely inside a cargo box ⏤ is critical and, if not done correctly, potentially dangerous to both to you and the motorists in your rearview mirror. So how much weight can a car roof actually hold?
The answer, of course, depends on your vehicle, whether you have a roof rack or carrier, and, from a legal standpoint, what the laws are in your state, or those states you’re driving through. According to the National Highway Traffic Safety Administration (NHTSA), there were 51,000 crashes, 10,000 injuries, and 440 known fatalities in 2010 as a result of debris flying off cars. The AAA Foundation for Traffic Safety turned up similar findings in a 2016 study, noting that “about two-thirds of debris-related crashes are the result of items falling from a vehicle due to improper maintenance and unsecured loads.” That report identified 200,000 crashes, 39,000 injuries, and more than 500 deaths between 2011 and 2014 as a result of road debris.
To identify how much weight you can safely load on top of your car, you must first pay attention to your car’s dynamics, as well as the regulations that govern your state. Here’s what you need to know about safely lashing stuff to the roof of your car.
Understand Your Car’s Dynamic Rating
The first consideration every motorist must take into account is what kind of car he’s driving. As you might imagine, the archetype of vehicle has a specific range of weights common with in the category. An SUV? You’ll hold more. A two-seater coupe? Likely much less.
Once you’ve found your specific car’s requirements, make sure you look for two numbers: a dynamic weight limit and a static weight limit. Dynamic capacity is the most important, as it’s the magic number for how much the roof can hold when the car is driving down the road. Hint: It’s not nearly as much as you’d think. On average, most cars, trucks, and SUVs can carry only about 165 pounds. Smaller cars have even less. And despite broad generalities regarding capacity, there are plenty of exceptions: A 2017 Toyota Rav4, a four-wheel-drive SUV you’d expect to be able to haul all kinds of crazy gear, is only rated to 100 pounds.
“Each vehicle will differ,” says AAA’s Tamra Johnson, “which is why drivers should consult their vehicle’s driver manual to determine weight restrictions.”
“Most vehicles are pretty limited; a couple hundred pounds max,” adds automotive writer Aaron Miller, who’s quick to point out that you also have to take into consideration the weight and shape of the cargo. “A kayak is light and aerodynamic. A mattress isn’t. Air can catch the mattress and cause lift, making the vehicle very unstable.”
The static rating, by the way, is how much the car’s roof can hold when the vehicle is standing still. It’s generally much greater than the dynamic rating because: a) the cargo weight is dispersed over the entire frame of the vehicle; and b) car roofs are by design built pretty tough (they do, after all, have to protect passengers in the case of a rollover).
But unless you’re planning to install a rooftop tent, you really don’t need to worry about your vehicle’s static rating. When it comes to hauling gear, the dynamic capacity is the figure you need to know ⏤ so once again, don’t forget to check that manual.
Your Roof Rack or Cargo Box
A roof rack obviously helps spread the weight across the car’s frame, as opposed to directly on the roof, but it doesn’t mean you can carry more stuff when the car is in motion. In fact, just the opposite. If you’re using a roof rack or cargo carrier, you need to subtract its weight from your total rating. For example, if your car roof is rated to 165 pounds, and your roof rack weighs 30 pounds, you can really only load 135 pounds of camping gear on top. The same is true of any crossbars you’ve installed to help fit your cargo box ⏤ they count too. Thule, the popular Swedish purveyor of all kinds of car and bike racks, puts this simple equation on its website: “Maximum roof load = load rack weight + any fitted rack accessories + the weight of the load itself.”
What’s equally important is to never exceed the weight limit of the weakest link in your roof-rack system. For example, “The maximum capacity of your roof-rack will be dependent on the lowest-rated part of the system,” writes etrailer, an online retailer of custom-fit towing accessories. “So, if you have a roof-mounted cargo box that has a weight capacity of 150 lbs., roof-rack crossbars that are rated at 200 lbs., and these are on a roof rated at 100 lbs., then you cannot load more than 100 lbs.”
This means you can buy the biggest cargo basket on the market, but if you’re trying to put it on a car that can only hold 75 lbs., you wasted your money. The same is true of that sweet rooftop tent. If it’s rated for 165 pounds, but you’re driving something like the aforementioned Rav4, think again. All in all, even if you’re not strong in math, just remember to always use the lowest-rated part as a guide.
Know the Law
When it comes to the law, the question isn’t, “How much stuff have you tied to the roof?” but, “What are the odds of it flying off?” Only 15 states have statutes regarding improperly or unsecured loads, while all 50 states have laws making it illegal to drop things from your vehicle.
“Currently every state has laws that make it illegal for items to fall from a vehicle while on the road,” says Johnson, “Most states’ penalties result in fines ranging from $10-$5,000, with at least 16 states include possible jail time as punishment.”
So, yes, a police officer who notices you driving a Smart Car with a grand piano strapped to the top probably will pull you over. But assuming it’s properly tied down and doesn’t fall off as they approach your vehicle, you’re not likely breaking any laws. If you’re driving through Georgia and that grand piano does fall off, get ready for up to a year behind bars.
Which is why it’s important to check the road debris laws in your state, and any that you’ll be driving through, before you start lashing old furniture onto the roof, if only to know what you’re in for if you screw up.
Learn How To Tie A Damn Knot
Or, at least how to take the proper precautions when securing cargo to your car. According to AAA, you should make sure that everything is properly “tied down with rope, netting, or straps, and that larger objects are secured directly to the vehicle.” They also suggest covering the entire load with a tarp to help secure items from possibly flying off while in motion.
Not sure if your granny knot or bunnies’ ears will securely hold? Odds are they won’t. Learning proper knots doesn’t require a return to Boy Scouts or the Naval Academy; rather, you can easily find one that, with practice, will become second nature. Our advice? Use the “Truckers’ Hitch Tie,” which will quickly and securely lash your cargo to you roof with easy (and zero Loctite).
If you’re using a cargo carrier, the load ⏤ and weight ⏤ should be distributed evenly across the box. Heavier items should go inside the car, not on top. “From a safety standpoint, you’d want the cargo as low as possible,” Miller says. “Keep the free weights inside the vehicle, pack the clothing on top.” Thule also notes: “With a load on the roof, the vehicle’s driving characteristics, its braking performance and its sensitivity to side-winds may change.” The explanation for this is simple: With heavier items on top, your center of gravity is higher, making turns more dangerous due to centrifugal force. It also exposes your rack and roof the greater stress and potential damage.
And finally, regardless of whether you’re helping a buddy move a mattress or are taking your collection of rare porcelain ballerina figurines to the park, check the load before you pull away. Then check it again. Make sure it’s tightly secured and your cargo box is locked. And if you want to play it safe, do as Thule suggests: “Check it after a short distance, and thereafter at suitable intervals.”