Subframes...Round or Square?

07-08-2001, 01:02 PM

Does anyone know which is overall better, round or square subframes?

dinomite · 07-08-2001, 03:38 PM

i have wondered this myself, i do know that you want full lengths though

elmir50 · 07-08-2001, 07:45 PM

Round tubing is much stronger structurally then square tubing. This is why it is used extensively when any kind of race car is built.

Moxie · 07-10-2001, 07:44 PM

True, round tubing is better for roll cages and tube chassis. However, for a weld-on subframe connector, you're welding it to a flat floor plan. Round against flat doesn't match up squarely, so the round tube subframes have flanges welded on the end.

Even with the flanges, round tube subframes don't provide as much surface area to be welded as square tube subframes. The extra strength of the round tube is more than offset by the decreased surface area of the welds. No matter how strong the tube is, that won't matter if the welds crack.

That was my long-winded way of saying buy square tube subframes.

------------------
Moxie Racing

The Nitrous Oxide Information Site

blueneonman1 · 07-11-2001, 12:43 AM

I would have to agree with "moxie". I have square subframes and my cousin has a mustang with steeda tube ones. He always raves about my Mustangs body stiffness over his and he thinks (even though he heard otherwise) that my subs are better.

------------------
Blueneonman - '95 5.0L Mustang GT Convertible | K&N Custom Cold Air Intake | FMS 9mm Wires | Hollow Cats | Flowmaster 2 Chambers | BBK Subframes | 6-pt Rollcage | King Cobra Clutch | FMS Adjustable Clutch Cable | B&M Short Throw | Coolest Neon Lighting on a Mustang EVER!

Homepage: http://www16.brinkster.com/blueneonman/

n20lx · 07-11-2001, 11:09 PM

A square tube is more resistant to bending than a round one for the same dimension 9for example 2" round v/s 2" square) Trust me. I'll do the math if you want. The reason round tubing is used in roll bars is it is easier to form. You couldn't make the bends it multiple directions with square tubing.

jimberg · 07-11-2001, 11:31 PM

Subframe connectors aren't there to resist bending as much as they are to resist stretching and compression down the length of the connector. This keeps the frame aligned. Your body will still twist somewhat (Think of a ladder), but it won't bend to the left or right.

------------------
351W 89 Mustang GT Convertible

jimberg · 07-11-2001, 11:49 PM

Oh, and round tubes resist twisting better which is another force that subframe connectors are going to encounter before they are subjected to a bending force. These two forces are why bicycle frames are made out of round tubing as well as race car chassis.

Round subframe connectors are better.

------------------
351W 89 Mustang GT Convertible

n20lx · 07-12-2001, 10:42 PM

A round tube will load more uniform in all directions, but your still gonna have more moment of inertia with a square or retangular tube. As far as stress due to tension this will rely on cross sectional area. i still think you see round tube in roll bars from formablity than from strenghth since the difference between the loading in the variuous shapes is slight. you don't see round bridge beam, building columns or even connecting rods. i don't have my books at the house so I will do some calc's at work.

jimberg · 07-12-2001, 11:34 PM

What I'm saying is that the major stresses that subframe connectors endure are not the folding of the car like it was a taco, hood to trunk. It is more from twist like a candy cane and bending from left to right like a brat laying on its side. (Gotta love food similes). Round subframe connectors will deal better with the bending and the twisting. Square may deal better with folding, but that's not really a problem.

Bicycles are all round tubes and they are straight so shaping can't be the reason why the use round tube. Nor is is aerodynamics.

------------------
351W 89 Mustang GT Convertible

Garyput · 07-12-2001, 11:53 PM

None of us here have near enough power to start bending and stretching square or round tube connecters when installed properly. The people that do have that kind of power are dealing with complete purpose built race cars .

I like square tubing myself, makes nice welds to the factory sub frames.

Phantom5oh · 07-13-2001, 12:55 AM

the best subframe connectors are square tubes that have been cut into the frame and welded in as if they were part of it... (also called through the floor subframe connectors)... they are the best that money can buy... much better than any other add on such as kenny brown or steeda or any other conventional connectors that you guys are arguin about... weld on, or even bolt on is CRAP!!! you need to have the floor pan cut and have square tube welded in... this is what the real racers have before they have a cage put in...

ps i am drunk buti know what i am talking about seeing as i build cages for a living... oh and I HAVE MORE THN ENOUGH POWER TO BEND ALL OF YOUR SUBFRAME CONNECTOR PUT TOGETHER...

------------------
CHECK OUT MY MODS

http://www.mustangworks.com/cgi-bin/...splay.cgi?1350

[This message has been edited by Phantom5oh (edited 07-13-2001).]

Dark_5.0 · 07-13-2001, 07:33 AM

Square sub frames are better cause the 90 degree angls at the corners replicate the triangle wich is the strongest geometrical
figure.

The more expensive bicycles use square tube on the main bar to add strength and take out flexibility.

Roll cages are a safety device thats why they use round tubing the smooth round wall of round tubing is much safer than square tubing square tubing has sharp 90 degree angles that would be dangerous in a roll over.

I use to be a welder and I am very good at it I have fabricated many metal structures.
Trust me square tube is much stronger and much better it is the angles of the square tube that give it the strength.

THE ONLY REASON PEOPLE SELL THE TUBE SUB FRAMES IS CAUSE THEY ARE SO EASY TO MASS PRODUCE.

------------------
88 mustang gt convertible bored to 306 BBk equal length headers mac cold air fender kit cowl hood nitto drag radials ford racing clutch flow masters h-pipe 160* thermostat 16 degrees of timing electric fan off 94' t-bird jacobs electronics cap and wires. Edelbrock 1 1/2 inch drop springs.
best 60 ft 2.14, best 1/8th 9.65, best 1/4 15.2 @89mph, Stock gears and 3000+ Altitude

n20lx · 07-13-2001, 07:37 PM

Seriously...
Get whatever you feel comfortable with. Like many said the difference from one to another at the levels they're loaded to will be slight. Somebody is gonna have to show me the math for me to believe that the round are stronger, but that's my problem (to paraphrase Buscemi in Fargo "I didn't come all the way down here to f###ing debate you". The best I have ever seen in action is 2x3 tube welded frame section to frame section through the floor. this will even stiffen a convertable.

07-08-2001, 01:02 PM	#1
jrfaraci Guest Posts: n/a	Subframes...Round or Square? Does anyone know which is overall better, round or square subframes?

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07-08-2001, 03:38 PM	#2
dinomite The Dude Join Date: Feb 2001 Location: Arlington, VA Posts: 1,262	i have wondered this myself, i do know that you want full lengths though

07-08-2001, 07:45 PM	#3
elmir50 Registered Member Join Date: Mar 1999 Location: Tsawwassen BC Canada Posts: 413	Round tubing is much stronger structurally then square tubing. This is why it is used extensively when any kind of race car is built.

07-10-2001, 07:44 PM	#4
Moxie Registered Member Join Date: Aug 2000 Location: Plymouth, MI Posts: 254	True, round tubing is better for roll cages and tube chassis. However, for a weld-on subframe connector, you're welding it to a flat floor plan. Round against flat doesn't match up squarely, so the round tube subframes have flanges welded on the end. Even with the flanges, round tube subframes don't provide as much surface area to be welded as square tube subframes. The extra strength of the round tube is more than offset by the decreased surface area of the welds. No matter how strong the tube is, that won't matter if the welds crack. That was my long-winded way of saying buy square tube subframes. ------------------ Moxie Racing The Nitrous Oxide Information Site

07-11-2001, 12:43 AM	#5
blueneonman1 Registered Member Join Date: Mar 2001 Location: Palm Harbor, FL Posts: 208	I would have to agree with "moxie". I have square subframes and my cousin has a mustang with steeda tube ones. He always raves about my Mustangs body stiffness over his and he thinks (even though he heard otherwise) that my subs are better. ------------------ Blueneonman - '95 5.0L Mustang GT Convertible \| K&N Custom Cold Air Intake \| FMS 9mm Wires \| Hollow Cats \| Flowmaster 2 Chambers \| BBK Subframes \| 6-pt Rollcage \| King Cobra Clutch \| FMS Adjustable Clutch Cable \| B&M Short Throw \| Coolest Neon Lighting on a Mustang EVER! Homepage: http://www16.brinkster.com/blueneonman/

07-11-2001, 11:09 PM	#6
n20lx Registered Member Join Date: Sep 1998 Posts: 495	A square tube is more resistant to bending than a round one for the same dimension 9for example 2" round v/s 2" square) Trust me. I'll do the math if you want. The reason round tubing is used in roll bars is it is easier to form. You couldn't make the bends it multiple directions with square tubing.

07-11-2001, 11:31 PM	#7
jimberg Registered Member Join Date: Oct 1998 Location: Rogers, MN Posts: 2,089	Subframe connectors aren't there to resist bending as much as they are to resist stretching and compression down the length of the connector. This keeps the frame aligned. Your body will still twist somewhat (Think of a ladder), but it won't bend to the left or right. ------------------ 351W 89 Mustang GT Convertible

07-11-2001, 11:49 PM	#8
jimberg Registered Member Join Date: Oct 1998 Location: Rogers, MN Posts: 2,089	Oh, and round tubes resist twisting better which is another force that subframe connectors are going to encounter before they are subjected to a bending force. These two forces are why bicycle frames are made out of round tubing as well as race car chassis. Round subframe connectors are better. ------------------ 351W 89 Mustang GT Convertible

07-12-2001, 10:42 PM	#9
n20lx Registered Member Join Date: Sep 1998 Posts: 495	A round tube will load more uniform in all directions, but your still gonna have more moment of inertia with a square or retangular tube. As far as stress due to tension this will rely on cross sectional area. i still think you see round tube in roll bars from formablity than from strenghth since the difference between the loading in the variuous shapes is slight. you don't see round bridge beam, building columns or even connecting rods. i don't have my books at the house so I will do some calc's at work.

07-12-2001, 11:34 PM	#10
jimberg Registered Member Join Date: Oct 1998 Location: Rogers, MN Posts: 2,089	What I'm saying is that the major stresses that subframe connectors endure are not the folding of the car like it was a taco, hood to trunk. It is more from twist like a candy cane and bending from left to right like a brat laying on its side. (Gotta love food similes). Round subframe connectors will deal better with the bending and the twisting. Square may deal better with folding, but that's not really a problem. Bicycles are all round tubes and they are straight so shaping can't be the reason why the use round tube. Nor is is aerodynamics. ------------------ 351W 89 Mustang GT Convertible

07-12-2001, 11:53 PM	#11
Garyput Registered Member Join Date: Jun 2001 Location: Salina Kansas Posts: 8	None of us here have near enough power to start bending and stretching square or round tube connecters when installed properly. The people that do have that kind of power are dealing with complete purpose built race cars . I like square tubing myself, makes nice welds to the factory sub frames.

07-13-2001, 12:55 AM	#12
Phantom5oh Registered Member Join Date: Mar 2000 Location: Boston, MA Posts: 334	the best subframe connectors are square tubes that have been cut into the frame and welded in as if they were part of it... (also called through the floor subframe connectors)... they are the best that money can buy... much better than any other add on such as kenny brown or steeda or any other conventional connectors that you guys are arguin about... weld on, or even bolt on is CRAP!!! you need to have the floor pan cut and have square tube welded in... this is what the real racers have before they have a cage put in... ps i am drunk buti know what i am talking about seeing as i build cages for a living... oh and I HAVE MORE THN ENOUGH POWER TO BEND ALL OF YOUR SUBFRAME CONNECTOR PUT TOGETHER... ------------------ CHECK OUT MY MODS http://www.mustangworks.com/cgi-bin/...splay.cgi?1350 [This message has been edited by Phantom5oh (edited 07-13-2001).]

07-13-2001, 07:33 AM	#13
Dark_5.0 Registered Member Join Date: Apr 2001 Location: Staging lane Posts: 4,337	Square sub frames are better cause the 90 degree angls at the corners replicate the triangle wich is the strongest geometrical figure. The more expensive bicycles use square tube on the main bar to add strength and take out flexibility. Roll cages are a safety device thats why they use round tubing the smooth round wall of round tubing is much safer than square tubing square tubing has sharp 90 degree angles that would be dangerous in a roll over. I use to be a welder and I am very good at it I have fabricated many metal structures. Trust me square tube is much stronger and much better it is the angles of the square tube that give it the strength. THE ONLY REASON PEOPLE SELL THE TUBE SUB FRAMES IS CAUSE THEY ARE SO EASY TO MASS PRODUCE. ------------------ 88 mustang gt convertible bored to 306 BBk equal length headers mac cold air fender kit cowl hood nitto drag radials ford racing clutch flow masters h-pipe 160* thermostat 16 degrees of timing electric fan off 94' t-bird jacobs electronics cap and wires. Edelbrock 1 1/2 inch drop springs. best 60 ft 2.14, best 1/8th 9.65, best 1/4 15.2 @89mph, Stock gears and 3000+ Altitude

07-13-2001, 07:37 PM	#14
n20lx Registered Member Join Date: Sep 1998 Posts: 495	Seriously... Get whatever you feel comfortable with. Like many said the difference from one to another at the levels they're loaded to will be slight. Somebody is gonna have to show me the math for me to believe that the round are stronger, but that's my problem (to paraphrase Buscemi in Fargo "I didn't come all the way down here to f###ing debate you". The best I have ever seen in action is 2x3 tube welded frame section to frame section through the floor. this will even stiffen a convertable.