Roll Cage Discussion

1995zj

1995zj

I'm addicted
Location
Herriman, UT
I know that cages have been covered PLENTY...but I haven't found the answer that I'm curious about.

So a buddy and I were discussing what tube diameter to use for his cage on his YJ. The option is between 1.5" .120 DOM and 1.75" .120 DOM. I used 1.5" .120 DOM on my ZJ and he was planning to use the same size. However, he had asked someone at BH and they had said that the 1.5" isn't strong enough and 1.75" is ideal. They told him that after one rollover the 1.5" cage would pretty much be destroyed and need to be rebuilt. Also that KOH was going to start making 1.75" the required size for cages due to this.

I know BH is a reputable source and they would know what they are talking about, but I don't get it, and if that's correct I'd like someone to explain why. I personally thought that 1.5" would be stronger, as it has a smaller inside diameter and would be less prone to denting/bending. Am I wrong here?

I'm sure people have tested this out....but I can't find anything. Discuss.

edit: If anything though, I don't see there being a difference in stregth at all...as they are the same wall thickness.
 
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HA. I don't care...I really am curious now. I'm no engineer, so I have no idea. I just want to see if someone here knows the answer or can point me to it.
 
I have no opinion about what size to use, it really depends on the intended use. In general bigger OD same wall tubing will be stronger when loaded in tension, compression, bending, and torsion. I'm not sure about dent resistance, but I think wall thickness would be more important than OD. Petersens had a test a while back where they swung a hammer and dented different tubes. I think they only changed the material, not the OD and wall.
 
I think the bigger diameter (same wall thickness) will be stronger because it has more surface area to spread the load over. I am not an engineer by any means though. I had my buggy built out of 1.75" because I wanted it to be a bit stronger, afterwards (and if I were to do it again) I'd most likely use 1.5". For a Jeep, I wouldn't hesitate to use 1.5".
 
Hmmm...didn't really think of the "spreading the load over a larger surface area". Good point there.

I think 1.75" should be used on a full tube chasis as well, mostly for looks more than anything though. 1.5" would almost look too small IMO. But for interior cages I think 1.5" is the ideal size, as anything larger seems to look too large.
 
1.75 is stronger. The bending moment is higher. That's a fact.


It all depends on weight, use and space.

look at score and bore and other race sanctioning body's rules and regulations. Roll cage tubing diameters are based on weight of the vehicle.

Recreational use vs. comp use obviously you should go with stronger and/or larger material.

For an interior cage 1.5 works to keep tubing tight to the body (you know this) but you also have a body to help protect you in a roll.

Whereas a Wrangler won't.

To my knowledge no one has been injured from using stronger material
 
1.75 X .120 wall DOM tubing is significantly stronger than 1.5 X .120 wall DOM tubing. For the weight of a recreational rig like his Wrangler, I would use 1.75. I used 1.5" on my old comp buggy because it was small and light, but used 1.75" on my old YJ and on my current XJ. I've seen strength data before. Shouldn't be hard to find...
 
RockMonkey said:
1.75 X .120 wall DOM tubing is significantly stronger than 1.5 X .120 wall DOM tubing. For the weight of a recreational rig like his Wrangler, I would use 1.75. I used 1.5" on my old comp buggy because it was small and light, but used 1.75" on my old YJ and on my current XJ. I've seen strength data before. Shouldn't be hard to find...
Click to expand...

So it's significantly stonger because there is more surface area then or....? I'm just trying to figure out what exactly makes it stronger.

This is good info, I just couldn't understand why it would be any stronger if it's the same wall tubing.

So would 2" be even stronger then? Or is there a point where it starts going downhill again?
 
1995zj said:
So it's significantly stonger because there is more surface area then or....? I'm just trying to figure out what exactly makes it stronger.

This is good info, I just couldn't understand why it would be any stronger if it's the same wall tubing.

So would 2" be even stronger then? Or is there a point where it starts going downhill again?
Click to expand...

"Stronger" is an interesting word... It is more resistant to bending, compression, and stretching the larger diameter, given wall thickness and materials are the same. Conversly, the larger diameter material is less resistant to denting, and can hold less internal pressure.

In terms of making a rigid structure (like a roll cage or tubular chassis) larger diameter tube will make a stronger structure. Yes, 2" is stronger than 1.75", but it's also heavier, more expensive, and more difficult to work with.

To wrap your head around it, imagine a bigger difference than 1.75 and 1.5. Imagine two 2 foot sections of tube. Both 1020 DOM tube, both .120 wall thickness. One of them is 1.75" diameter, and one is .75" diameter. Intuitively, which one is easier to bend? Which one would make a more suitable material for a roll cage? The same difference applies to 1.75" and 1.5", just on a smaller scale.

1.75" is more rigid, and more suitable for vehicles over 4000 pounds or so. The only significant benefit to 1.5" tubing is weight savings, which is why you tend to see it on light-weight competition buggies.
 
Another point that I just thought of is the joints on the tubing where the weld would be. There would be a larger surface area to weld if the tubing was a larger diameter. This may also make the 1.75 a little better to use versus the 1.5.

LT.
 
There is a lot more to building a cage than just the diameter of the tubing. You can easily use 1 1/2' tubing to build your cage, however you will need to add more cross members, supports, triangulation etc to make it strong enough to with stand the potential hard roll. Then you need to factor in the additional cost and weight of the added supports.

Some may say, well I don't wheel much and I'm mostly a pavement pounder so a strong cage really isn't needed.
Well, when you are doing cartwheels down I-15 you might be glad you invested in the 1 3/4" DOM.

Just my $1.28
 
Shawn said:
There is a lot more to building a cage than just the diameter of the tubing. You can easily use 1 1/2' tubing to build your cage, however you will need to add more cross members, supports, triangulation etc to make it strong enough to with stand the potential hard roll. Then you need to factor in the additional cost and weight of the added supports.

Some may say, well I don't wheel much and I'm mostly a pavement pounder so a strong cage really isn't needed.
Well, when you are doing cartwheels down I-15 you might be glad you invested in the 1 3/4" DOM.

Just my $1.28
Click to expand...

Yeah, I've already built my cage in my ZJ out of 1.5" DOM. I guess more research should've been done on my end in the first place, but I feel I did pretty well with the design of the cage and I'm not worried about it holding up.

http://www.rockymountainextreme.com/showthread.php?t=68670

I was mostly just curious about this is all.
 
The desert guys recommend 4000 pounds or less 1.75 120 wall
5000+ 2.0x120. They used to use smaller but the crashes are worse as the vehicles get faster. We crashed a class 8, (5000 lbs+) first hit was on the top at around 50 mph (caught the front end and landed on the top can you say front flip). This was 15 years ago and it was built out of 1.75 4130. Personally I think 1.75 is enough if it is 120 wall.
Just my 2 cents
 
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