Which one do I choose? - While you can't go wrong with either design, use the following to determine your order: If strength is your number one priority, choose the boxed design. Boxed tubing is torsionally stronger than round tubing however you will lose approximately 3/4" of ground clearance when using this style. If your car is lowered and ground clearance is the prime concern, go with the tubular model. While round tubing is not as strong torsionally, there are other features to these subframe connectors that make them more rigid than most other tubular models available.

www.bmrfabrication.com

 

Torsionally; that's "twist", and not "bend in half", right? I always thought round tubing was stronger than square, always, but that's more for "bending in half" strength, I guess. Thanks for that info!

 

I was always told a tube is stronger than a box. The Box has corners that bend and pinch easier then a tube. I'm happy with my tubular Alston SFCs. Unless you are off roading, I'd imagine both boxed or tubular would be up to the task however. My Alstons are barely visible from under the car. They have saved me over some rough pavement, they make great skid pads!

 

Hmm. . . I seem to recall superpools and when they are square and rectangle and even rectangular with rounded ends all of them needed supports on the straight parts. Funny, on my round 33' diameter swimming pool we never needed any sort of support braces. I have no idea which one is stronger nor do I care, lol. If you're that concerned with ridigity get a cage. And for those worried about Spohn's redesign, go ahead, search the boards for bad comments about his products.

 

soulbounder

This has nothing to do with cars, but I figured I'd spurt out some knowledge. The reason a round pool requires no supports is that the water wants to exert pressure evenly in all directions, pushing the walls of the pool round. On an oval or rectangular pool, the same is true. Without any supports on the straight walls of the pool, the water would try to push them out and cause the sides of the pool to bow outward. Some older oval shaped pools had metal straps that ran under the pool from side to side to prevent this from happening. I installed pools for a couple of years.

 

Yea, I know pools have nothing to do with cars but round vs. rectangular and which one being stronger or more common can be seen in almost everything and in everyday applications.

 

I believe round tubes are more likely to "bend" compared to a similar dimension rectangle tube, but the round tube will resist twising(torsion) much better than the rectangular tube. Pretty much the exact opposite of what the first post was saying. I'm not positive though, I'll bust out my notes on deformable solids if everyone disagrees, maybe I didn't remember too well.

Think of drive shafts/axles etc. are all round in shape resist twisting, while more rectangle shapes(I-beams) are used in structures to resist bending. I imagine the way most SFC are designed so the forces acting on them try to "bend" the SFC instead of twist it, and that's why the rectangluar tubing is supposed to be stronger.

 

A guy back home made a square drive shaft once cause some one told him it would never work...... He smoked alot of weed though.

 

Round is stronger , bottom line. However many cars have square tubing and they work great. I believe square would be easier to weld in along the floor.

 

All things equal, round tubing is stronger torsionally. However, the original post did not give dimensions or wall thicknesses. So, a given section of rectangular tubing could indeed resist torsion better than a certain section of round tubing.

 

I would think as stated before that round would resist twisting while square would resist bending. I think that bending is what they are there to resist right.