2nd Gen Homemade Roof Rack Hardware and Thule Cargo Box - Jeep Compass Forum
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post #1 of 6 Old 07-09-2019, 08:45 PM Thread Starter
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2nd Gen Homemade Roof Rack Hardware and Thule Cargo Box

I bought a Thule cargo box this spring when they want on sale, the "Large" size (16 cubic feet). That alone was expensive enough, but I could not stomach handing over $250+ for the Mopar or Thule brackets and cross rails.

Besides the cost itself, as we have seen in other people's photos they sit comically high on the roof (not something I need since I don't have the sunroof), and the brackets wrap over and totally wreck the good looking roof line on the rails. They also just plain don't look very sturdy, IMHO.

I decided to go my own way. Grabbed some scrap angle iron from an old bed frame, a spare piece of 3/4" metal conduit, and a handful of bolts and I was on my way. Cut four pieces of the angle iron, measured and drilled them out with my cheapie drill press. Chopped up the conduit and bored some holes in those, and I was pretty much done.

I was in a hurry to go camping so I only had time to paint the brackets, which was the important part since those are intended to be permanently affixed to the inside of the rails.

The conduit crossrails I will be pulling off to clean up and paint. I was thinking of just putting black foam pipe insulation over them and 3D printing some caps for the ends. Thats all in the aesthetics department, but we went hundreds of miles with our tent and my golf clubs up in the cargo box and it worked great.

These are the brackets I made just before installing them:




A couple of quick videos:




The Thule box has four claws that can grab onto just about any shape. I could have cut and bolted a couple of 2x4s with black indoor/outdoor carpet stapled to them and it probably would have worked just as well, but the metal tube seemed less obtrusive. I don't intend to leave the tubing up there when the cargo box is not in use.










Thoughts and things I would do different:
The angle iron works great, but I wish I would have used better paint and had more time for it to harden up. Actually was thinking dipping them in a bedliner or something durable would be the best route. I wish I would have welded the 5/8" nuts on the bottom of the brackets, it would have made putting the cross rails on and off easier and less potential to scratch the roof fumbling around, definitely lay down some cloth to protect the roof.

I used stainless steel 1/4" bolts and blue locktite so other than touching up the paint I don't plan to take these off unless I need to, but if I did I'd weld the nuts on and paint them better or coat with bedliner.

The brackets are the most important part. Literally anything can be a cross rail now. If I was hundreds of miles from home and really needed it, a couple pieces of board would do so long as you had access to a saw, drill, and some bolts.

I had hoped to do something different to try to put the weight more on the factory rail itself, rather than on the brackets and bolts, and I may eventually get to that but I have not put anything heavy enough on top yet to worry about it. Feels super solid when you grab ahold of one of the bars.

--------------------------

Initial thoughts on the Thule cargo box: The "Large" size is pretty darn huge. Its really nice in terms of added storage, but to get it far enough backwards to be sitting decent on the roof you have to unscrew the AM/FM antenna, and it has tremendous drag on the 65-75 MPH highway. My gas mileage has taken an enormous hit, as low as 22 MPG on some short trips driving into the wind, 24 MPG on a 65 MPH highway in a rainstorm, really struggling to get 26-28 MPG on fair weather days. The box is aerodynamic but you can still hear the air rushing around it, about as loud as having a window cracked maybe, so not totally objectionable or loud but you won't forget that its there.

The worst part is that its the straw that breaks the camel's back for the transmission. I don't know about everyone else's car but despite having the longest legs (final drive ratio), mine loves to get into 8th gear on the highway, it always has the first 28k miles of owning it, and yet as you know it takes very little in terms of a hill or an incline and it has to drop to 7th. Well, add one large cargo box to the roof and now its dropping to 7th all the time, and I mean ALL the time, for the slightest hill or gust of wind. Its bad enough that it will eventually give up and hold 7th on its own, something I've only previously seen when towing a washer, dryer, and standing freezer that was up in the wind. Knowing this, I now slap it in manual mode as soon as I get to highway speed to force 7th just to avoid the first 10 downshifts before it catches on. On a windy day, dropping to 6th is slightly better (mileage-wise).

I had expected some extra drag and mileage loss but its so extreme, it just emphasizes how close the engineers shaved it when they ran all the numbers and figured out engine power and gear ratios. Adding this cargo box threw it all out of whack and in two tanks of gas it has not seemed to adjust to it either. So, its nice to have but I won't be leaving the box up there when I'm not using it, because I don't like having to use manual shifting just to go to work and back without the transmission shifting 64 times.

I bought the largest box I could get. All I really needed was enough length for downhill skiis, so to anyone else looking at something similar I would say don't over-buy because I'm looking at $50 more in gas to go to the mountains with the box on vs box off, and I probably didn't really need 16 cubic feet. Of course at slow speeds the drag is negligible so if you only drive around the city and don't go miles and miles on a 4 lane highway every day for work won't be so bad.

That my 2 cents.
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post #2 of 6 Old 07-10-2019, 12:23 PM
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Thanks for a very informative post!

My only experience with stuff on the roof was carrying my canoe with my old Patriot. I estimate that it caused an economy drop of about 15%, i.e. from 30+MPG to about 26MPG.
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post #3 of 6 Old 07-12-2019, 11:01 AM
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How thick is the angle iron ? It looks on the thin side and I'd be worried about it bending over time. I bought some rails off of Amazon a couple months ago for $100, they're aesthetically pleasing and also handle the weight of anything I can throw in my roof rack for camping
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post #4 of 6 Old 07-12-2019, 04:45 PM Thread Starter
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Quote:
Originally Posted by 84z28
How thick is the angle iron ? It looks on the thin side and I'd be worried about it bending over time. I bought some rails off of Amazon a couple months ago for $100, they're aesthetically pleasing and also handle the weight of anything I can throw in my roof rack for camping
I feel there is a bit of humorous irony here, that the guy with aftermarket ABS (plastic) brackets and thin aluminum crossbars is concerned about the durability of my all-steel hardware

Sorry I'm just being funny. I don't think there is any concern about the strength of my brackets, they are about 1/8" thick steel cut from a bed frame. Those bed frames easily support the weight of a mattress, box spring, and two large Americans doing their nightly business without issue for years on end. Pretty confident they can hold some golf clubs and skis up. Don't underestimate that EMT steel tubing either, that may only be 1/16" thick but its very strong and rigid, the length I cut for this project I don't think the average guy could bend with his bare hands. The factory side rails will have issues long before there is any potential of problems with the homemade hardware. That's how homebrew stuff goes, it gets way over-built usually.

I looked at the aftermarket cross rail kit you got, at one point it was as low as $59.99 but I don't trust the plastic brackets for the long-run. Plastic tends to get brittle with age and constant exposure to the elements. My brother had a plastic-bracket roof rack on his honda, and it was actually a brand-name thing like Thule or something recognizable, but last winter his brand new snowboard got some road rash when it came flying off on the interstate. Driving at high speed in high winds the ABS brackets cracked and broke off.

Now, "aesthetically pleasing", safe to say thats not my strong suit. I'm very utilitarian with just about anything I construct. I could get some more pieces of steel tube and try to put a nice gentle curve in them with the pipe bender at the old man's shop, but I don't think I will bother. This Thule box seems like it likes to lie flat on a flat bar. I will paint the bars black at some point and possibly use something other than a nut for the spacer, get some end caps on it and all that, but when the Thule box comes off so will the bars so since they're not being left up there I'm not too worried about it.

------------------

Side note, I used AlphaOBD to force the 2WD (dyno) mode just for fun this morning and it is a calm nice day out, got back up to 28 MPG average for a 20 mile run on the 65 MPH highway with the box on top. Its a bit annoying to imagine regularly plugging in the adapter and opening the app just to force 2WD but on a road trip it might be worth the effort if I'm using a lot of autostick, otherwise I think it stays in AWD when shifting manually even cruising on the highway. I don't have any evidence or proof of that yet but when we go on our next road trip I can do some logging with AlphaOBD when the wife is taking her turn to drive and I should be able to find something that tells me whether the PTU or rear clutch is engaged, both to find out if autostick forces AWD and whether or not the 2WD dyno mode really works. I'm pretty sure the dyno mode does work though, the gas mileage went up and normally when cruising and slapping it in autostick it is immediately followed by the humming sound and a click of the rear axle locking in, didn't get that today.
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post #5 of 6 Old 07-12-2019, 08:52 PM
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They're aluminum bars with die cast mounting brackets, so a hair better than ABS and has a 165lb load capacity. You should have jumped on them if you saw them for $59.99

Quote:
Originally Posted by arudlang View Post
I feel there is a bit of humorous irony here, that the guy with aftermarket ABS (plastic) brackets and thin aluminum crossbars is concerned about the durability of my all-steel hardware

Sorry I'm just being funny. I don't think there is any concern about the strength of my brackets, they are about 1/8" thick steel cut from a bed frame. Those bed frames easily support the weight of a mattress, box spring, and two large Americans doing their nightly business without issue for years on end. Pretty confident they can hold some golf clubs and skis up. Don't underestimate that EMT steel tubing either, that may only be 1/16" thick but its very strong and rigid, the length I cut for this project I don't think the average guy could bend with his bare hands. The factory side rails will have issues long before there is any potential of problems with the homemade hardware. That's how homebrew stuff goes, it gets way over-built usually.

I looked at the aftermarket cross rail kit you got, at one point it was as low as $59.99 but I don't trust the plastic brackets for the long-run. Plastic tends to get brittle with age and constant exposure to the elements. My brother had a plastic-bracket roof rack on his honda, and it was actually a brand-name thing like Thule or something recognizable, but last winter his brand new snowboard got some road rash when it came flying off on the interstate. Driving at high speed in high winds the ABS brackets cracked and broke off.

Now, "aesthetically pleasing", safe to say thats not my strong suit. I'm very utilitarian with just about anything I construct. I could get some more pieces of steel tube and try to put a nice gentle curve in them with the pipe bender at the old man's shop, but I don't think I will bother. This Thule box seems like it likes to lie flat on a flat bar. I will paint the bars black at some point and possibly use something other than a nut for the spacer, get some end caps on it and all that, but when the Thule box comes off so will the bars so since they're not being left up there I'm not too worried about it.

------------------

Side note, I used AlphaOBD to force the 2WD (dyno) mode just for fun this morning and it is a calm nice day out, got back up to 28 MPG average for a 20 mile run on the 65 MPH highway with the box on top. Its a bit annoying to imagine regularly plugging in the adapter and opening the app just to force 2WD but on a road trip it might be worth the effort if I'm using a lot of autostick, otherwise I think it stays in AWD when shifting manually even cruising on the highway. I don't have any evidence or proof of that yet but when we go on our next road trip I can do some logging with AlphaOBD when the wife is taking her turn to drive and I should be able to find something that tells me whether the PTU or rear clutch is engaged, both to find out if autostick forces AWD and whether or not the 2WD dyno mode really works. I'm pretty sure the dyno mode does work though, the gas mileage went up and normally when cruising and slapping it in autostick it is immediately followed by the humming sound and a click of the rear axle locking in, didn't get that today.
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post #6 of 6 Old 07-13-2019, 05:27 AM Thread Starter
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Quote:
Originally Posted by 84z28
They're aluminum bars with die cast mounting brackets, so a hair better than ABS and has a 165lb load capacity.
I must have been looking at something different altogether, I thought was the same thing but it only advertised 150 pounds. The cheap set I saw was also shipped from china via the "you'll get it someday" type of shipping, otherwise normally right around the $100 mark.

--------------------------

I pulled the Thule box and bars off tonight. Only took a few minutes but I still wish I would have welded the big nuts on the brackets to make it even easier. Everything still looked good and felt solid. About three tanks of gas I ran with it up there, hopefully my mileage will rebound. Probably not right away though, I have a 1200 pound trailer hooked up have to make a 300 mile run tomorrow, will be 2000 lbs coming home.

I tell you what, 1200 pound trailer + thule box made for some really crappy gas mileage for a few miles coming home today from picking up the trailer. ~20 MPG, not even hardly any wind I don't think. Was still around 24-25 most of this week with just the box up top. I'm honestly considering selling the large box and buying something much smaller. The extra space is nice but its excessive extra space, I could have had half as many cubic feet and as long as it was still long enough for our skis in the winter and big enough to squeeze our tent in the summer it would have done what we needed. I mean, I like the space but its hard to be ok with dropping so much economy on a long road trip and the nail in the coffin has to be having to manually shift to save on the tranny constantly downshifting. That makes it harder for my wife to take a turn driving, having to explain "well thats a big hill better drop one gear". [20 minutes later on flat ground] "Did you not ever shift back into the higher gear after that hill?" She is understandably not into that kinda thing. I'm not a huge fan of it myself. We do so much 65-75MPH highway driving, I just don't see how this is going to work.

I could put our skis in a ski bag and bungee them to my cross rails and still get them to the mountains, I don't really have to have a box at all other than the nice security/locking aspect of it. I've seen some pretty skinny ski boxes from Thule that maybe won't rob up to 1/3 of my mileage.

I don't know what to think of it for sure yet. I'm no aerodynamics engineer, my wife wonders if putting our homemade cross rails so low hurt mileage because the space for air between the roof and the box was narrower than it would have been otherwise. Could be? I guess unless/until someone else buys a big box like that on regular cross rails it will be hard to say, not enough data and experience.
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