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Discussion Starter #1
I've got to give Twilightzero credit for most of the thought that went into this project. I just got my E a couple months ago and wanted to get a roof rack. So I started saving some $...and then I see it! DIY "Ghetto Fabulous" Roof Rack 2.0

I'm generally up for a good challenge (I do industrial machine repair) and can't believe I didn't think of making one to begin w/.

Now the wheels are turning, and I'm hoping to make some improvements to Twilightzero's design. The changes wont be cheap, but the rack will be cheaper than OEM/Yakima/Thule, and accessorizing will be easy.

My first e-shopping was done at WW Graingers.com and a search for "T-slot extrusion" showed me exactly what I was looking for.

2RCP8


I'll be using 2 of those cut down to 58-60", (I haven't decided on a length yet)

I've ordered slot covers to cut down on wind noise, end caps to give it a "finished" look, and a couple packages of nuts/bolts to hold everything in place. That totaled $102.xx from Graingers, and the M6x1.0x20mm bolts w/ lock washer and fender washers cost $20.91 (thanks ACEhardware :( )

Total cost so far=approx.$123.xx

Checking McMaster-Carr showed me even more products and the prices (catalog) are cheaper for comparable products.



However Graingers is more convenient, I don't have to pay shipping, and I get a discount through my work account.

I was going to use 2"x2"x2" C-channel like Twilightzero, but a quick search of the scrap bin at work turned up some 2.5"x2" extruded aluminum I-beam. So that will become my stand-off(s) after being cut to size.



Alright, I didn't read his instruction thoroughly enough, and cut my pieces into 5-1/4" lengths which are too long. So they're going into the mill to be shortened tomorrow.
 

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Those I beam extrusions would have been nice to have 5 yrs ago when I made rack. I had to settle for bolting two pieces of 1 1/2" angle extrusion together to form an equivalent bracket.
 

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Discussion Starter #3
I think the extruded aluminum T-slot has been around for over 5 years. But I'm not sure when it became readily available through industrial suppliers.

I finished the initial assembly/installation today, and will only be making minor changes mechanically. The button head screws holding the inner part of the bar clamp have to go. They were a total PITA to tighten, and will be replaced w/ 1/4-20 hex-head bolts. I also will probably be removing the slot covers from the front/rear of each bar, I don't think those surfaces will generate much noise, and I wont need to remove the bar to add attachments there. That means I'll most likely be covering the bottom slot but we'll see how noisy that is first.

Then I'll probably make a wind deflector...It'll give me somewhere to put stickers. :|

So here are the pics for today...







 

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That is very cool!! It probably has a lot to do with the color of your E though :D
 

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Discussion Starter #6 (Edited)
lol Thanks NismoGriff and twrundar!

And, here's the list of parts I used.

( 2 )2RCP8 t-slot extrusion 72" ($24.69 list) $22.22
( 2 )2RCR7 2pk end caps ($2.83 list) $2.55
( 8 )2RCT2 t-slot covers ($4.65 list) $4.19
( 2 )2RCT8 dbl nut 6pk ($7.67 list) $6.90
+tax $5.43
=$102.29
+ Bolts/Washers/etc ($20.91)
=$123.20 total

I could have saved $16.76 (+tax) by only ordering half the T-slot covers I did, and another $6.90 on extra dbl nuts.

The I-beam didn't cost me anything, but I'll try to find a similar product, and cost for estimating. If anyone should want to do this...
 

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Discussion Starter #7
*CAUTION!!! SUBSONIC WAVE GENERATOR!!!!!!!!!

I'm not talking about some whimpy background hum. This is shake the mirrors/feel it in your chest sonic boom!


Apparently this set-up is quite harmonic. After typing my previous reply I took the E out for a ride to the liquor store to grab a few celebratory beerz. On the way there I was surprised to hear what I thought was the car in front of me BOOMIN' their system. On the way back, with no other traffic around, it became apparent that my new roof rack could be renamed "Ryno-HAX"!

I've been to the HOME DEPOT and, wrapped the bars w/ foam pipe insulation. Went out for another ride and got the same results after exceeding 35mph.

I'm going to have to fabricate some type of wind deflector to get the bars out of the wind, or try to pre-load the bars with an arc. But that may be more difficult than I'd like this project to be.
 

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My homemade rack was quite noisy, starting at about 40mph. I used Yakima bars, but they were closer to the roof.

The foam sort of worked. My next version was a 1x2 piece of wood held at angle below the front bar (using stock Yakima bar clamps). Later I refined it to a 2" strip of aluminum. I just needed enough to change the flow of air between bar and roof.

With your extrusion you could have bad noise as the wind flows over the slots, but you have covered those, haven't you?
 

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Discussion Starter #9 (Edited)
Yeah they're all covered by the foam insulation. The top/bottom are the only slots I'm willing to cover permanently. I was hoping to get some linear bearings for the bars to make canoe loading extensions with. But If I cant get this "BOOM" issue under control w/o covering the front/back/bottom that option will most likely be out.

I'm going to cut a piece of LEXAN(tm) tomorrow for a deflector and see what I can make for brackets. My goal is to make this a 1-man operation, and workable in the dark, if at all possible.

I'm thinking cam-locks for my accessories. (any input from experienced "rackers"???) That should make things easy to manage single handed.
 

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my rack based on the ' ghetto 2.0 ' rack has some wind noise , but barely noticeable , flex and harmonics must play the tune and it is transmitted thru the mounts , perhaps a slip of inner tube rubber between the I beam and the roof might dampen the tune ? :)
 

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also rubber between the crossbar and the ibeam, and rubber washers on the mounting bolts. This should isolate the vibration some.

For giggles. load something heavy on it and see if the vibration stops?
 

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Discussion Starter #13
Thanks! The rubber bushings are a great idea. I'm not sure how well they'll work (given the harmonics of the cross bars). But easy enough. So consider it done.

I had considered doing 'in line' bars, and thought they would be useless for my application (canoe hauling). Since I'd have to put the cross bars on every time I wanted to 'paddle out' I might as well just have cross bars.

I spent some time working on the wind deflector today. It's not done yet, and may be revised. I'll post some pictures when I get something ready to test.

I'm also considering "raising the bar" to see how that affects noise.
 

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for some reason this vibration/harmonics got me thinking...

I would venture to guess that the vibration/noise is due at least in part to air turbulance, caused by the shape. Twi's rack has holes and lets some air pass through it. Your rack is covered and creates a vacum on the trailing side of the square tube. If you made some sort of partial wing on the trailing side I would bet the noise would stop.

There is at least one pilot on the EOC and I'm sure he could confirm or deny my suspicions. I'm not sure of how it work exactly but I'm sure it's related to bernoulli's principle and the change in air pressure on the trailing side of the square tube.

You need to give the tube a wing. Not a typical wing but a symmetrical wing... same on the top and bottom.

Can't remember the Pilot's name but he has a plane on his avatar.

Hope this helps.:confused:
 

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Drill 1/4" holes (about 3" apart) dead smack in the middle of the cross bars all the way from one side to the other. Straight through so you can see through them when you're looking at them from the front of the car. That SHOULD take care of the weird hum. Sounds stupid, but there's a damn good chance it'll work.
 

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Yakima and Thule bars also have noise problems. That's why most have fairings. Pipe insulation can also help. In some cases, just wrapping a rope, or bungee cord around the bar (spiral fashion) is enough to alter the air flow. Owners have also found that some accessories, including cargo boxes, gets rid of the noise.

Note that the fairing is mounted just on the front bar. The rear one does not need anything.

I tried a short clip on airfoil that Yakima sells, but it didn't do anything. That's why I went with the homemade fairing.

Experience tells me that the critical area is the gap between the front bar and roof.
 

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Discussion Starter #17
I wish drilling holes were an option. But I'm sure they'd ruin the structural integrity of the bars.

I fashioned some 1/4" thick rubber bushings for the 'feet' and the cross bars today. I used some washers under the outer bolt holding the bars down to pull the bars down further on the outside and create a slight arc. It also bent the 'I'-beam slightly, but I can add some support there, and it's not much of an issue.

I bolted it all up, and went out for a test drive. I didn't put the pipe insulation around them, and only had the slot cover in the top. I figured this would be the noisiest configuration. It wasn't bad. The bushings reduced the subsonic noise to a quiet drone that could easily be talked over, and doesn't shake the mirrors off. I could finally hear the wind noise from the bars turbulence.

The fairing mounts are proving to be difficult compared to the rest of this project. I've hacked some brackets out of aluminum sheet and 1"x1" angle. They'd probably work fine, but I'm not happy w/ them as a permanent fixture, and will work on making something out of bar-stock in the mill at work.

And I'll get pictures of the progress up soon.
 

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Discussion Starter #18
Alright it's picture time!

First up is the arch in the bars.



I removed the washer and lock washer to get the bolts to start.



And finally you can see how the I-beam has been distorted by the pressure bending the bar puts on them.

 

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Drill the holes. It's not like you're trying to build a bridge out of these things.

The holes will have absolutely no affect on the structural integrity of these bars. At least not for the application you're using them for.
 

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Discussion Starter #20
You're right I'm not trying to build a bridge. I'm trying to build the lightest most structurally rigid roof rack I can w/o spending much $. (and yes I understand that I could have built something cheaper)

Anyway....

I fitted the fairing to the front bar today. I'm not very happy w/ the brackets that I made to attach it, or the shape of the fairing blade. They do their job though, and that's alright I can make something better later. Unless I move on to other projects...

So I drove about 60mi at freeway speeds up to 75mph, and It's as quiet as a church mouse! I'm thrilled w/ the improvement.

I'll post some pics tomorrow. I'm not sure how well the Lexan will photograph but I'll try.
 
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