Question about FR mounts

[MOAK]

Hello all, it’s been a while. We finally made the switch from ground tenting to Rooftop tent. After our last two trips it is obvious we should have made the switch years ago. Our new RTT scales out at 162lbs and it was previously mounted with the long bolts and stainless bars. I’ve ordered an awning for our kitchen and moved the tent up on frontrunner’s tall brackets. I’m using grade 8 bolts. I’m a bit concerned about using only four bolts to hold this thing down. Obviously using 2 more of the fr feet would make it stronger, but necessary? Thanks in advance .

 

[NatersXJ6]

In my opinion, grade 8 is completely unnecessary, and 4 bolts should be plenty to secure the tent when properly tightened in normal driving conditions.

more important is making sure they stay tight, good locking nuts are a decent idea, and I have always put fender washers in the tent floor side to ensure the best load spread I could get.

 

[MOAK]

Cool, I use grade 8, as a matter of course, everywhere that is steel to steel, wood to steel, any old bolt will do, with lock nuts, regular & fender washers, everywhere. Normal use? Miles & miles of washboard, occasional rock crawling and lots of ledges, along with highway miles, during all four seasons.

 

[Lemsteraak]

Rather than just thinking about how to bolt your system down, maybe look at the whole package. We did a couple sled tests (simulated crash tests) as well as a crash analysis many years ago. We were fortunate to have one of the US vehicle manufacturers put our tents on some vehicles they were crash testing. This was on the "universal" mount system that virtually all the roof tent manufactures have adopted. I was surprised by the results, the tents and bar system passed but all had slid about two inches because of the collision force. In the case of an actual collision, a rear ender, the tent slid back about two inches on the mounts.

I know you are designing a very different system but you may wish to factor in the forces in a collision. In the case of our crash analysis, it was a crash that our field tester, a good friend of mine was involved in. Unfortunately, there isn't a lot of information to go on as there are no tests to my knowledge above 165 pounds. Most of the roof bar mounting systems are only tested that high so this would be the weak link. In fact some of the bar feet are made of high strength plastic.

It sounds like your equipment is very capable but you still might want to inspect all the mount points. Vehicle manufacturers don't give out a lot of information on the strength of their mounts. Even the rack manufacturers don't always know. We had downrated a very popular SUV to our tents 125 poundss or less. I was at SEMA and talked to the OEM rack manufacturer. They correctly pointed out how you could pick up the whole truck with the rack. It was well made and designed with 2 inch steel tubing. The vehicle manufacturer was installing their rack with sheet metal screws when it came into the country, they weren't aware of that. Check to see that your mounts are bolted to the vehicles internal roll cage, or frame.

I hope this helps, I know I'm not giving a proper answer to your question but thought this information might prove helpful in your build.

 

[MOAK]

Rather than just thinking about how to bolt your system down, maybe look at the whole package. We did a couple sled tests (simulated crash tests) as well as a crash analysis many years ago. We were fortunate to have one of the US vehicle manufacturers put our tents on some vehicles they were crash testing. This was on the "universal" mount system that virtually all the roof tent manufactures have adopted. I was surprised by the results, the tents and bar system passed but all had slid about two inches because of the collision force. In the case of an actual collision, a rear ender, the tent slid back about two inches on the mounts.

I know you are designing a very different system but you may wish to factor in the forces in a collision. In the case of our crash analysis, it was a crash that our field tester, a good friend of mine was involved in. Unfortunately, there isn't a lot of information to go on as there are no tests to my knowledge above 165 pounds. Most of the roof bar mounting systems are only tested that high so this would be the weak link. In fact some of the bar feet are made of high strength plastic.

It sounds like your equipment is very capable but you still might want to inspect all the mount points. Vehicle manufacturers don't give out a lot of information on the strength of their mounts. Even the rack manufacturers don't always know. We had downrated a very popular SUV to our tents 125 poundss or less. I was at SEMA and talked to the OEM rack manufacturer. They correctly pointed out how you could pick up the whole truck with the rack. It was well made and designed with 2 inch steel tubing. The vehicle manufacturer was installing their rack with sheet metal screws when it came into the country, they weren't aware of that. Check to see that your mounts are bolted to the vehicles internal roll cage, or frame.

I hope this helps, I know I'm not giving a proper answer to your question but thought this information might prove helpful in your build.

Thank you, this is the kind of information I was seeking, so your answer is very proper. I have thought out and built the entire package and the weak link is the mounting system. With the kind of testing you have witnessed, I'd say my build and the Front Runner products, combined with grade 8 hardware is in excellent shape. The rack is bolted to heavy 2x2 angle using 5, 5/16" grade 8 bolts at each end, which is welded to heavy 2x2 tubing which has been welded to the new 2x2 sub-frame of the trailer. A secondary reason for the re-enforced frame was to equalize the center of gravity once the RTT and rack were bolted up top. I do have a tendency to try and keep and build equipment that is as overbuilt as our 80 series. A lifetime ago I was a driver instructor out in California. We hired guys off the street and taught them to operate small dump trucks and construction equipment trailers, hauling skip loaders, 8-12 ton rollers, back hoes, paving machines, etc. I could never impress enough, the importance of making the equipment one with the trailer, by properly binding everything down. If there were an accident, no one wants equipment flying off of the trailers. Nor do any of us want our racks and all of our gear to go flying, let alone fall apart after traversing untold miles of rough and/or washboard roads. I think I might take the time to post up my trailer build. I can't weld, but we have a club member that works in stainless food grade that welded everything up for me.

Thanks again, with your information I see no need to add another pair of brackets.

Subframe- uprights- rack