250 lbs dynamic load - RTT mounting question, custom option needed?

[RickDenverRealtor]

I have been looking at a RTT that is heavy, 250 lbs. Don't judge that part, please merely help with a solution if you have one.

The towers that support / connect the Thule and Yakima cross bars to our factor side rails max out at about 165 lbs (though a store told me 220 lbs).

Perplexity.ai states: The maximum dynamic (driving) load capacity for Thule and Yakima crossbars is typically around 165 lbs (75 kg) across two bars.For Thule crossbars like SquareBar Evo, ProBar Evo, AeroBlade, and WingBar Evo, the minimum dynamic weight capacity required for a rooftop tent is 165 lbs (75 kg). Anything heavier than 165 lbs requires the roof rack's capacity to match or exceed the tent's weight.Similarly, Yakima states that the dynamic load limit for their crossbars should not exceed 165 lbs. This is the combined weight of the rack system and any cargo that can safely be carried while driving.​

Ignorant question, but would adding a 3rd or 4th cross bar help distribute the load and make this mount safe?

I have not been able to find OEM rails or cross bars to support this load.

Input on a solution welcome.

Please do NOT reply with "camp on the ground, buy a lighter tent" etc. as that is not helpful to solving the problem.

Thank you

 

[ROBERT BONNER]

I come from a long line of roof over loaders and having seen many roof crush tests and roof overloading failures....I have a few comments and suggestions:

1) If you have a moon roof, stop reading now and forget it. Assuming you don't have a moonroof, consider the following:
2) I think it is highly unlikely that you'll find any aftermarket roof rails that will advertise the ability to carry more than Ford specs for the roof for liability reasons if nothing else.
3) Roof load limits are based on a variety of factors that you may not have considered and should before proceeding. The main thing that Ford looks at when establishing the maximum is it's affect on vehicle dynamics during evasive maneuvers, including all of the software that is pumping rear wheel brakes, adjusting steering boost, ELSD, transmission, boost, etc., etc. during that 3/10's of a second that you are avoiding contact with a teenager texting her boyfriend while trying to occupy your lane and hers simultaneously. The more weight, the further from the roll center of the vehicle, the more affect on vehicle roll, yaw and associated risk for roll over, oversteer, etc. This doesn't mean you should decide to not to overload it...just be aware that if you end up having to dodge an idiot on the road, the truck WILL respond differently.
4) Another aspect is that the roof load is part of the GVW, probably biased towards the rear GAWR - every pound you put on the roof is a pound you can't put in a seat, on the floor or off the tongue. These trucks have an alarmingly small amount of payload. Put a full load of fuel in, 2 adults, a spread of 4 kids, a dog, as much luggage as you can cram in, a cooler off of the tongue and 250# on the roof and you will definitely be over the GVW and likely over the rear GAWR as well. If in doubt, run it across axle scales at a truck stop. Overloading the GVW for long periods will accelerate failures of lots of things in addition to messing with dynamics. Once again. If you are aware and accept all of these things, go ahead, it is your truck.
5) Assess the bending strength of whatever cross bars you have. Place them on a smooth surface (whether you choose to use 2, 3, 4 bows), load them with your payload and measure the deflection at the center, then try to "bounce" the load and see if the bows flex. If you can't measure deflection under these conditions, go ahead and put it on the roof. Then drive it at freeway speeds, try to find some crosswinds and satisfy yourself that your load isn't "singing" or doing any wind driven "bouncing". If you satisfy these requirements, you won't damage the truck structure with 250# on the roof. If you can't find bows to satisfy these requirements, have someone weld some up out of steel pipes with ends that properly attach to the roof side rails.


More than you ever wanted to know, or perhaps all things you already know. Good luck.