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how strong are the roof bars??

6K views 18 replies 7 participants last post by  shu2kill 
#1 ·
hey... im about to get a 2002 Xterra, and i plan on building a camping vehicle that is equally well suited for some mild offroad as well as for highway driving and pulling a boat... i camp a lot, and these camping trips can be up to 4 days, and besides all the camping equipment, we carry a lot of climbing equipment as well... so the first mod i want to do is a homemade roof rack to increase the space... i have been thinking about fixing it to the original roof bars with 4 U bolts, one on each corner...

do the roof bars are strong enough to hold a rack and equipment?? the rack will be very light, but once ready for camping it can be quite heavy, with the backpacks full of equipment, ice chests, and supplies... i would try to put the heaviest equipment inside, but the rack would get some weight as well...

will it hold?? i dont want it to tear the bars from the roof, i dont even know how they are hel to the roof yet... i have seen pictures of roof racks with spare tires, ice chests, and stuff, but im not sure how they are fixed to the truck...
 
#3 ·
thanx... i think i saw the weight rating of the small basket it has at the front of the rails, but i dont remember if it also had the total weight... 140 lbs would be fine, its almost 65 kg, and i guess the rack will weight 5 kg at most...

so 4 U bolts would be fine??
 
#4 ·
I would anticipate 4 U-bolts being fine. Just make sure the hardware is tightened properly...and use lock tite on the threads to keep them secure.

I haven't seen your design or anything, so it's hard to tell where it would fail...but my guess would be not at the U-bolts
 
#5 ·
thank you!!

i plan on building it of such a size that it fits inside the roof bars, so it wont be very high... im not much of designing on paper, i just think about the design, and once everything fits in my head, i build it... i have built front and rear bumpers for my jeep, rock sliders, 2 cargo baskets, toolbox, and several other things, and i rarely draw anything.... so i guess i will be taking pictures of the builds for the How To forum but i wont upload sketches or drawings beforehand...
 
#8 · (Edited)
here is a secret from the world of engineering:

Factor of safety...or the "factor of ignorance"

When designing something and determining a max allowable load...the rating is often anywhere from 20-50% on the conservative side...and often failure criteria is not always a catastrophic failure...IE a bowing tube on the rack, or a certain angle of deflection that is allowed. Also...if that 250 pound brother was distributed to the entire roof rack, by a basket bolted at various locations...the load is even easier to carry by the roof rack.

If that 120 max load seems maybe borderline for your needs or on the low side, rest assured if you are at 150 pounds or 160 or even 200...if that weight is in a basket that is resting on the roof rails and distributing the weight to multiple points on the roof rack, you are probably in no danger

That being said, if you think you may be on the heavy side of the max load rating, having 6 or 8 u bolts distributing the weight even more so each section of the rack holds less weight will mitigate the heavier load. Depending on your design, u bolts will probably be enough in the sense the u bolts wont break, but you don't want the middle of the basket to sag under the weight either! That is where the 6-8 U-bolts would help out the most
 
#9 ·
here is a secret from the world of engineering:

Factor of safety...or the "factor of ignorance"

When designing something and determining a max allowable load...the rating is often anywhere from 20-50% on the conservative side...and often failure criteria is not always a catastrophic failure...IE a bowing tube on the rack, or a certain angle of deflection that is allowed. Also...if that 250 pound brother was distributed to the entire roof rack, by a basket bolted at various locations...the load is even easier to carry by the roof rack.

If that 120 max load seems maybe borderline for your needs or on the low side, rest assured if you are at 150 pounds or 160 or even 200...if that weight is in a basket that is resting on the roof rails and distributing the weight to multiple points on the roof rack, you are probably in no danger

That being said, if you think you may be on the heavy side of the max load rating, having 6 or 8 u bolts distributing the weight even more so each section of the rack holds less weight will mitigate the heavier load. Depending on your design, u bolts will probably be enough in the sense the u bolts wont break, but you don't want the middle of the basket to sag under the weight either! That is where the 6-8 U-bolts would help out the most

so true...

since im planning on building the rack of such a size that it sits inside the roof rails, it will be more or less square, so it would be small... thats why i had considered 4 U bolts only.... but if i decide to build it on top of the rails, it would be bigger, and maybe 8 bolts would be better, or at least 6, 3 per side....
 
#10 ·
Oh I see...so a square type basket in between the side to side rails?

I was thinking of a rack with no cross members, and a large basket in between the long front to back rails...the entire length of the roof type of thing

But that is where your design comes into play...the stock roof rack will be able to do what you need it to do :)
 
#11 ·
well, i havent decided yet on the type of basket.... i thought a square one to fit between the rails and the cross members... but maybe that one will be too small for my needs, and the space on top of the crossmembers would be useless... so maybe removing them and making a longer basket?? i know i want to keep the roof rails, but the crossmembers i dont mind removing them...

im not sure, im still researching, looking for ideas and opinions...
 
#12 ·
No worries on the rating of the rack. I hauled a 230lb couch tied down with 4 ratchet straps up there for 30 miles at 60 or so MPH in 15MPH crosswinds.
The truck would have flipped before the rack gave out.
Yes, it was a bone chilling drive.
Yes, if Aunt Edna dies you'll be able to strap her up there and dump her at Cousin Normy's place.
 
#13 ·
the way i would look at it is...

if you do a basket that is square between the side to side cross members....what would you do with the extra length of the roof rack? You would have some space at the end and at the front probably...does that extra space give you any benefit? I would think it would just be wasted space...

Heck, you could even make the basket the entire length of the roof...u bolted to the roof rack...so it hangs down below the roof rack...and still have room to put the cross members in place...maybe use the cross members as a sort of divider to wedge a cooler against the side of the basket or keep things from sliding around...or extra security on top to keep something laying flat, etc...the cross members being adjustable allow you to move them anywhere you want...I'd try to integrate them into your basket idea maybe
 
#14 ·
well, it seems i still have a lot of research and thinking to do... im picking the truck tomorrow, so i havent been able to give it a good stare and begin picturing things... i could even do a mock up of the regular equipment i carry to give a better idea...

as soon as i decide i will try to do a sketch, but most probably i will end up just building it and taking pics...
 
#15 ·
O.k. I have attached pics of my rack which is similiar to the DEPHEP rack. I had to build mine because DEPHEP's wouldn't ship (too big) to where I live. I normally (when going camping) carry a 5 Gallon Jerry Can (40lbs), a full size spare (50lbs) and two large North Face bags (total of 80lbs). The roads that I drive on here would be considered horrible by US standards and camping consists of 30KM of trerrible roads/trails that are rutted from trucks with 18inches of ground clearance. Additionally, I stand on the rack while packing it and have never had the rack I built or the factory rack flintch.

I have topper tape between the my rack and the factory rack to prevent slipping and only four hooks securing it to the factory rack. I think that this is the best way to go since it distributes the weight to the entire factory rack. Anyway it works well for me.

Oh. one thing to keep in mind if you go this route. The factory bars on the xterra are not flat. There is a bow in them and when you build your rack you will have to factor that in or you can pull your factory rack out of the roof with the aftermarket rack. Let me know if you have any questions.
 

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#18 ·
Yes, there is a bow. It is ever so slight however when you put flat steel on curved aluminum you can guess which will win. I made the top portion than put a small bow in it using weight and a forklift! Also, the topper tape helps fill the gap if you don't get the bow exact. Put a 4' or 6' level on your bars and you will see it. Here are some more pics.

One of the pics show the rear of the rack that is made for a steel 20L/5gal jerry can. The loops that you see on the top of the rack are for the rachet strap that holds the can down (offset because of where the nozzel is). I don't worry about the wind resistance of it too much since when the jerry can is up there it has a full size spare that sits in front of it and the can is only a couple inches taller than the spare.

You can see when I was testing (still in primer) it with the cooler, spare and can on it. I could have fit another cooler up there, it has a lot of room.

I am looking at doing a bolt on shovel & machette (the thing to have in Africa) mount for it one of these days.

Any questions just let me know.
 

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#19 ·
ok ok, thank you!! i thought they were leveled...

anyways my idea was to put the rack inside the rails, not on top of them... this way, the bow will not be a problem... however nothing is decided yet, so i will keep this in mind in case i decide to mount it on top...

thank you!
 
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