Load bearing capacity for roof

Just out of curiosity, does anyone know how much static weight the roof is rated for? I see a bunch of 4Rs with full-length roof racks, roof-top tents, etc., and was wondering how much weight the roof is rated to support.

 

Owners manual 2021 4Runner - Page 190 - "Do not exceed 120 lb. (54kg) cargo weight on the roof luggage carrier."

 

OP is asking how much weight the roof will hold, not the rails.

 

120lb dynamic I'm assuming?
Static, not in motion, maybe higher.
There's actually a ton of conversations on this out there.

My 64" basket weight capacity is 250lb. Certainly that's static, it's Amazon.

 

Aren't we taking about the same things when we say how much will the roof can hold. I mean when you put crap on the roof, no one's talking about without the side rails even. Factory rails static weight, or factory cross bars static weight is the question

 

I think 120lb mentioned in manual it's a rating for factory crossbars.

 

I think Toyota has been intentionally conservative and vague on roof capacity. Tons of people running lots of weight on roof.

Common sense goes a long way not pushing it to the limit putting you or others at risk.

Quoting @McSpazatron from another thread. He articulated this nicely:

Ok, here are my thoughts on the whole roof rack business. I realize everybody figures out their own solution, and I respect that because we’re figuring out as we go.

Toyota has set the weight limit they’ll vouch for, and it’s pretty low. Even though aftermarket roof racks might publish higher dynamic and static weight limits, I highly doubt it’s a limit for anything other than the integrity of the mounts and rack itself. I have not seen any rack manufacturer test an installation dynamically until the mounts get pulled out of the roof, the roof caves in, or the body gets racked sideways.

It’s important to keep in mind that the side to side rocking motions that happen on any mild trail going at moderate speeds, or off camber angle changes can put huge pulling loads, compression loads, and racking loads directly on the roof structure.

Beefy mounts may be strong, but it doesn’t help if it’s stronger than the little T nut hardware arrangement on the inside of the roof. How much racking does it take to pull those through the roof in a hard side-to side motion? In the few years I’ve been looking, I haven’t seen any aftermarket company do actual destructive testing to get weight limit numbers I’d be willing to trust.

So in the meantime, anybody loading up an aftermarket roof rack is truly on their own to figure it out. That’s why it’s good to actually try to visualize the forces that get imparted to the four mounting points. Take for example that spare tire. It weighs about a 100 pounds. If you put it on top of a 5 foot structure, then swing that structure side to side with the pivot on the bottom, how much force is required to accelerate it and decelerate it? I can easily imagine on a road that rocks you side to side, shock loads could be 3 or 4 times the weight of the tire applied sideways on the mounts and roof. How many of those cycles can the roof take before a fatigue failure of the roof steel?

That’s what I think about whenever I’m considering how to load the roof.

In my case, I decided to make a simple rack that uses the stock rails and mounts, because I’d rather trust the wide weight distributing mounts. The wide pad contacting the roof limits fatigue forces at least into the roof, and the plastic construction will probably break before forces get too out of hand. Maybe…because I don’t know that…I havent destroyed my 4runner roof to find out. That’s why anybody going above toyotas limit is completely on their own.

So like has already been mentioned, be strategic in how you use the roof if you are concerned about longevity. The best bet is to keep the roof for bulky lighter options as much as possible. Remove it or unload it when the storage is not necessary to limit metal fatigue of the roof. And don’t assume just because somebody on the youtube has 1000 pounds on it, that it wontultimately break the body of the vehicle

 

OP didn't mention anything about the rails. He asked how much weight the roof will hold. There are aftermarket roof racks that will handle a lot more weight than the factory set-up. I read the OP's question that he is curious at what point does the roof start to bend/dent. Not when the rails bend.

I could be wrong. Wouldn't be the 1st time.

 

I guess I should clarify that I'm asking about the roof itself, not a rack or cross-rails. I used to load plan for USAF cargo planes, and that's what got me to thinking. The standard 463L pallet we used was rated at being able to carry 10K lbs, but we normally used 7500 lbs for planning purposes. So you've got 7500 lbs on a 108" x 88" aluminum pallet that gets loaded onto an airplane. Obviously, the floor load limit on the plane has to be greater than what's being put on it. So an analogy in the 4R world is you've got a full-size roof rack that has fuel cans, water jugs, high-lift jack, roof top tent, and whatever else people put up top, being supported by the roof. If the weight of that stuff was spread evenly across the roof rack, that would spread the load across the roof itself as well (assuming the strength of the roof is the same across the whole thing).

So is it safe to assume that as long as you don't exceed the limits of the roof rack or cross rails, the roof in turn can safely support it as well (ignoring center of gravity and center of balance calculations)? My initial guess is yes, because the dynamic and static loads for these roof baskets / rails seems fairly small, all things considered?

 

Wouldn't it be safe to say that Toyota has designed the roof structure so that the A, B, and C pillars and the cross girder connections between them, need to be able to support the weight of the vehicle (at least temporarily) in case of a rollover? I'm not saying you can put 5000+ pounds up there, but I think it would support more weight than any sane person would want to carry on the roof. I think the limitation is on the fasteners to the roof. IDK. My logic could be failed here...

 

I agree weakest link is brackets in roof. Rollover testing is done but I don't think any testing for rating gear on roof.

 

Could be...but also, a big factor to consider when loading up a roof rack is the dynamic (moving) versus static (stationary) ratings. In an airplane, the loads have to be restrained from forward, aft, vertical, and lateral movement, in multiples of g-factors (3gs forward, 1.5gs aft, 2gs vertical, etc). This is normally achieved using straps or chains, but the single point of failure is the ring on the floor that these restraint devices attach to. So I'd agree that however the roof rack is mounted to the roof would be of primary concern, especially when the rack is loaded and the vehicle is in motion.

 

Toyota will never answer this question as it would most likely create potential liabilities for them. They only need to provide proof of what it can withstand in a rollover. I've never heard of weight on the top causing structural issues with the roof as of yet. The problems come with the addition of the weight and how that can affect rolling over. But a larger roof rack and items on top can also catch garages/trees/etc and that in turn can fuck up the roof. As far as a # of lbs that will make the roof give ... we need someone to volunteer to keep adding shit up top until it happens to find out

 

What I know is when I replaced my stock rack with RCI, it came with metric property class 10.9 bolts. The stock bolts were unmarked.

 

I think the answer is, don't be the Clampetts.

 

This and what Catbrown357 said.
It's good this info is getting some attention. I did see that video someone posted about load ratings and failures from an Australian gent. It came to light because their truck roof rack was held in by some rivets. Obvious point of failure there. Would be nice to see someone cut open a 4 runner pillar and see how the mounting points are held on. Maybe a YouTuber could do some stress testing. I also agree that to some degree there may be a roll over rating as well. In my opinion if you feel like your stressing the roof maybe look at alternative solutions. TOW it Don't Haul it. There are so many tiny cargo trailers on the market right now you could even put a roof top tent on if that's what you chose.

 

That's exactly what I was thinking...a small 4'x8' trailer with drop sides could do wonders in replacing the Beverly Hillbillies approach to packing out...

 

Glad someone else knew what I was referencing there! I'm sure there are plenty who don't!

 

Not for everyone for sure but I'd rather add a few things to the top when needed than deal with a whole separate trailer and maintaining that too. Different strokes

 

The roof steel is curved, so distributing weight evenly across its surface would not be practically feasible. It’s pretty much the reason it has a roof rack. Also, it’s pretty apparent that the surface of the roof span was not designed to carry any load directly on the tin. Just push lightly down on the center of the roof tin with one finger, you’ll see. It literally flexes down with almost no pressure. The stamped raised ridges on the steel don’t really add load capacity either. I bet those are there to keep the roof steel from bouncing up and down while driving.

Also, there’s no use in drawing any analogies between a load floor and a roof. They are designed different to meet different needs and dont share any structural similarities. Unless the roof is also designed as a floor (which is not the case in the 4runner).

But if you’re asking how much weight it takes to collapse the pillars, it’s way more than the weight of the 4runner. I can imagine you could put several thousand pounds of soft material on it and would not collapse in a static situation. Granted, the roof tin would be permanently deformed, and probably some of the internal cross structure, but it wouldn't technically collapse.

You can put a lot on the roof directly if you don’t care about how it will look afterward



But the pillars do have limits

 

I think Toyota only discloses the dynamic weight for the rails. Probably for legal reasons.

The front runner rack is damn strong. If you need to run a lot of weight on the roof I'd recommend a very strong rack.

 

I was wondering the same thing about the roof tin. Why would anyone want to load weight on the roof directly? And if using a rack, why exceed the recommended weight limit of the rack?

 

Aftermarket ppl are just welding sht together… just don’t be a torch bearer for a brand new consequential product

 

I wasn't asking about loading anything directly on the roof, I for one surely wouldn't do that. But anything that someone puts in a basket or on the rails/crossbars is in turn supported by the roof in one way or another (drip rails, pillars, whatever). If someone's not paying attention, I could see where it wouldn't take much to exceed the stated weight limit of a basket, just because there's space. I was overseas, and we had added plywood sides to a flatbed trailer (to hide the cargo), and we were putting crates of anti-tank mines on it. The folks started loading the trailer at the front, stacking the crates about four high. After a couple of rows were done, it dawned on me that they couldn't stack them that high on the rest of the trailer, because it would exceed the weight limit. So after doing some quick calculations, we stacked them lower for the rest of the trailer, and were good and road-legal. 'Course one thing that could prevent someone from exceeding the weight limit of a roof basket is the fact that you'd have to get those heavy objects up there in the first place (think fuel and water jugs, high-lift jack, etc). From what I've seen and has been posted in here so far, if folks use common sense when loading anything up top, they'll be good (for the most part). Just be aware of the higher center of gravity resulting from the added weight and bulk up top, exceeding the weight limit of the roof doesn't appear to be an issue.