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Steel Tube strength: building a roof rack...

Keitha

Keitha

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I am designing and building a roof rack for my 1991 Suburban. I plan to cary miscelanious gear/stuff, and occasionaly a 17' Canoe and/or surfboards. Nothing too heavy.

My question is to help me decide what steel to build it out of. I do not want to overbuild this and have it weigh a ton.
I am deciding between 1" or 3/4" square steel tubing. I am going to build a 4x8 basket design.

I like the idea of 3/4" as it should be less wind resistance.
What is stronger: 1" square tube at 14guage or 3/4" square tube at 11guage? They both weigh the same/ linear foot.

Do you think 14 guage, 3/4" would be strong enough?

thanks,
 
I vote for the 3/4". As long as you brace it together enough and have an adequate number of supports to the roof, it will hold just fine.
 
I would build it out of aluminum.

1) Lighter

2) Strong enuff for light duty

The draw back would be cost and having to use Tig or bolt it together.
 
Aluminum is out of the question because of cost and I have to justify using my Miller 211.
 
they make a spool gun for that 211:whistle: but aluminum bleeds. you'd end up with streaks running from it on your paint. The 3/4 would be fine even at the 14ga. if its built right. Round would look better and be even less drag.
 
I would personally make it out of 1x1" 1/8th" wall and have the deck made out of 1/8" flat expanded metal, that way if you do haul something heavy you wont damage your roof rack trying to load it up there. It shouldn't weigh that much (if it were aluminum I would skip the spool gun and go for TIG mainly because of the thin wall, and possibly tight spaces, also spool guns are a b*tch to dial in based on the impurities in both the parent metal and the brand of wire). You know that these old square bodies slice through the air like a sledgehammer, if wind resistance is a concern ad a wind deflector in front of the roof rack, it will help with drag and keep all the bugs off of your equipment:waytogo:.

I plan on building two individual roof racks for my K5 out of 1" square tube that would be stout enough to load a spare tire up there (although mine will be mounted on my rear bumper), it will also double as a light bar and headache rack for hauling metal or lumber.
 
Another vote for the 3/4, why because I think bungee cords and tie downs would hook better to the smaller stuff
 
The larger tube is more resistant to bending but either size is plenty fine. The difference in wind resistance will not be measurable.

-Brian
 
Thanks guys: I think I will go with the 3/4". I will post pictures as it goes together.
 
shady said:
they make a spool gun for that 211:whistle: but aluminum bleeds. you'd end up with streaks running from it on your paint. The 3/4 would be fine even at the 14ga. if its built right. Round would look better and be even less drag.
Click to expand...

As if steel tubing won't bleed. I've never had aluminum bleeding, but it may depend on the series of aluminum your using. Stick to some 6000 series and you'll be fine. If your really worried, give it a coating of paint on top. I'd rather have a little aluminum bleeding (if it happens) than rust bleeding from some tubing.

40-70 lbs of tubing, vs about 10 to 20 lbs of tubing, its a lot of weight up top.

If you need an excuse to use your welder, I'd make it out of both aluminum and steel- you can fabricate the brackets and what not, and you can bolt square aluminum tubing to it. Lightweight, strong, and you don't need to do anything too special.
 
Pookster said:
...40-70 lbs of tubing, vs about 10 to 20 lbs of tubing, its a lot of weight up top.

If you need an excuse to use your welder, I'd make it out of both aluminum and steel- you can fabricate the brackets and what not, and you can bolt square aluminum tubing to it. Lightweight, strong, and you don't need to do anything too special.
Click to expand...

I'm kind of liking this idea.:waytogo: I will play around with the design and see what I can do.
 
In Costa Mesa, CA I wouldn't worry about either steel or aluminum bleeding like I would in the midwest or east. Just paint the thing and be done.

I would definitely strive for light weight. It's about efficiency and proper engineering of whatever material you use. There's a tendency for folks to have very overly heavy roof racks.

If you're serious about lowering drag, you could use streamlined tubing (they make both steel and aluminum). One of these tubes perpendicular to the flow could have as much as ten times less drag than a round tube of the same span.
Aerodynamic_Tubing.jpg
 
with that tube you could lower drag by angling it right and lifting off:haha::haha:



That stuffs cool. I've never even heard of it. I'm gonna have to look it up.
 
That tube is cool, but looks expensive! My main thought in lowering wind resistance is probably pretty silly given that it is going on a 1991 Suburban. I defenitly want to keep weight down. Too much weight on the roof will make this thing a bit tipsy.

Here are the weights/foot for different square tube:
1" -------------------------- 3/4"
11g = 1.44 lbs/ft ---------- 11g = 1.03 lbs/ft
14g = 1.03 lbs/ft ---------- 14g = 0.75 lbs/ft
18g = 0.63 lbs/ft ---------- 18g = 0.47 lbs/ft

Given that I will have a bit over 80', it does make a difference.
 
shady said:
with that tube you could lower drag by angling it right and lifting off:haha::haha:



That stuffs cool. I've never even heard of it. I'm gonna have to look it up.
Click to expand...
for small amounts I just mail order it from aircraft spruce.

I figured you can built yourself a beefy rack for not much money.if you want the streamline stuff it will be more costly. 99 dollars for 6 feet of 6061 t6 aluminum. I'd skip it

However I'd get it measured out (the straight runs) and have them cut them to roughly the same length. For example, I'd use 6061 t6 square tube 3/4" .049 wall thickness. Its plenty strong, and 5 feet of it weighs a little over a lb. Its about 4-5 dollars a foot.

Make 4 corner jigs out of steel: You can do 4130 cromoly, or just use regular mild steel.. your choice. You make em into almost like a corner clamp. for welding, so that it has a ID of 3/4" .

For weight carrying, you can do all sorts of cross beams and what not. Lots of choices, you can drill and bolt them to the aluminum frame. Just use some stainless bolts.

http://www.aircraftspruce.com/menus/me/aluminum_6061t6square.html
 
shady said:
with that tube you could lower drag by angling it right and lifting off:haha::haha:



That stuffs cool. I've never even heard of it. I'm gonna have to look it up.
Click to expand...

Aesthetically, it's great looking ... but remember our trucks have the aerodynamic coefficient of a brick, a three-ton brick. I think you'd need a wing off a 747 to get our trucks airborne :haha:

-- A
 
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