Mark's roll cage question list

Quote
NoCoast
I see two other bars from the top of the roll cage holding that strut top pretty firmly in place.
Now I suppose that could bend upward and the rear half of the car could tear off?
Shell longevity? I thought we were supposed to get on stage and rally ASAP and wreck the first car. Those two bars cost $100 for the pair and none of the six customers I've done cages for these past few months have requested it.

$100??
ASAP?

The fact that they haven't requested is is no point, they didn't think of it and as a shell prep guy you should educated them...
2 pieces of tube 18" long cost $100?

Why are you arguing? It's simple and makes shit stronger for hardly any weight or bother.
This is hard?

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

I'm still not seeing it. There are two bars that go to that location already.

Two bars, 6-7 feet of cage, four profiles, four tubes to weld, time.

---

Grant Hughes

John is right here and not just for his example of strut-tower forces. That bar also helps keep the sill-bar and door-X in tension during a side impact instead of just pulling the foot of the main-hoop forward. At the front end of the car, a tube from the foot of the A-pillar to the top of the strut tower does the same thing at that end....

---

____________________________________________________________-

One. Class -- 2WD

www.quantumrallysport.com

http://www.facebook.com/home.php?#/pages/Quantum-Rally-Sport/281129179600?ref=nf

Quote
Josh Wimpey
At the front end of the car, a tube from the foot of the A-pillar to the top of the strut tower does the same thing at that end....

There it is. That makes more sense. But doesn't the main hoop X also do some of that?

---

Grant Hughes

Quote
NoCoast
I'm still not seeing it. There are two bars that go to that location already.

Two bars, 6-7 feet of cage, four profiles, four tubes to weld, time.

OK, don't see it.
You can learn Grant by asking "I wonder why Ford always put a bar from base of main hoop upwards when the rules don't require it?"

And on my cage its a total of 2 x 32" or 64" or about $52 if it was 4130 CrMo bought in short quantities...but it ain't or $28 for DOM Mild Steel Tube A513 TYPE 5

(just happen to be ordering steel for the next run of 50mm things cause all the tubes I have for 50s are standard length for normal fronts and Subies rear and BMW fronts need a longer tube....)

You don't want to...fine. I was suggesting to Mark

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

I added that bar to the 2nd Merkur. Bottom of the main hoop to the rear tower.

Quote
john vanlandingham
You can learn Grant by asking "I wonder why Ford always put a bar from base of main hoop upwards when the rules don't require it?"

Well that settles it. The Ford guys OBVIOUSLY had engineered it and designed it and realized that without it EVERYONE would die and the rule makers were stupid for not requiring that single bar!

---

Grant Hughes

It is certainly interesting looking at the cages you guys are fitting and how there is a lot more to them than is required over here in the UK.
I have not yet seen this years MSA rule book, but unless there has been a drastic change then just a basic six point cage with single door bars with regard to the cage is all that is needed to get the car logbooked and out on stage.

The curved non intersecting door bars pictured, and the discussion on them at the start of the thread makes sense. I have considered the benefits of having a slight convex bend (facing outward) in certain tubes that would need to compress first to go "over centre" before it started to encroach in on the occupants space. The door bars and roof section of the main hoop seem places this would be a possible benefit. An impact at these points would need to push and move the supporting tubes of these curved members to allow the length to be wide enough to let the member go "over centre", where as a straight tube can just start bending inward from the start.
Think I might check with my local technical scrutineer on a whether the curved door bars can be used here in th UK.

---

Disappointingly not yet a Jackass

Wouldn't curving the bar weaken it's resistance to force in the same direction as the bar?

Tim.

Quote
danster
An impact at these points would need to push and move the supporting tubes of these curved members to allow the length to be wide enough to let the member go "over centre", where as a straight tube can just start bending inward from the start.

No, a straight door-bar tube in a door opening strike with a tree is in tension immediately upon impact. ---Yet another reason to use the diagonals from the feet up to the strut towers both front and rear.

The curved outward tube is first in compression between the main hoop and front stay but has a tremendous amount of leverage due to the angles and moves over-center with very little resistance before coming into tension. And, once it come into tension, the twisting and deformation associated with coming over-center has weakened at least one element (the tube, or one of its connections, or connected tubes) and thus compromised the total tension load it can support before failure. This is why NASCAR bars are frowned upon and require a lot of additional tubing (mass & connections together) to be certified for US rally.

Straight bars (or at least all bars in a single plane between the main hoop and front stays) in the door opening... Please

---

____________________________________________________________-

One. Class -- 2WD

www.quantumrallysport.com

http://www.facebook.com/home.php?#/pages/Quantum-Rally-Sport/281129179600?ref=nf

Quote
Josh Wimpey
No, a straight door-bar tube in a door opening strike with a tree is in tension immediately upon impact. ---Yet another reason to use the diagonals from the feet up to the strut towers both front and rear.

The curved outward tube is first in compression between the main hoop and front stay but has a tremendous amount of leverage due to the angles and moves over-center with very little resistance before coming into tension. And, once it come into tension, the twisting and deformation associated with coming over-center has weakened at least one element (the tube, or one of its connections, or connected tubes) and thus compromised the total tension load it can support before failure. This is why NASCAR bars are frowned upon and require a lot of additional tubing (mass & connections together) to be certified for US rally.

Straight bars (or at least all bars in a single plane between the main hoop and front stays) in the door opening... Please

Nice explanation.
Here's my favorite "thinking outside the box" cage recently... Keep a close eye on the green bars...




We chatted about his design and he modified and ended up with this.

---

Grant Hughes

Quote
Josh Wimpey
No, a straight door-bar tube in a door opening strike with a tree is in tension immediately upon impact. ---Yet another reason to use the diagonals from the feet up to the strut towers both front and rear.

The curved outward tube is first in compression between the main hoop and front stay but has a tremendous amount of leverage due to the angles and moves over-center with very little resistance before coming into tension. And, once it come into tension, the twisting and deformation associated with coming over-center has weakened at least one element (the tube, or one of its connections, or connected tubes) and thus compromised the total tension load it can support before failure. This is why NASCAR bars are frowned upon and require a lot of additional tubing (mass & connections together) to be certified for US rally.

Straight bars (or at least all bars in a single plane between the main hoop and front stays) in the door opening... Please

You know that makes perfect sense. I can grasp the high leverage aspect and the resultant slack then needing taken up.
Straight bars as you describe are effectively in tension the whole length between the shock towers offering a pretty large area of support to absorb the force.
It's always good to hear different views as it helps to build the fuller picture and understanding.
And the good thing is no pipe bender is now required by me as a bonus!

EDIT, Blast! Well no pipe bender till Grant posted that pic!

---

Disappointingly not yet a Jackass



Edited 1 time(s). Last edit at 01/23/2013 04:41PM by danster.

Quote
NoCoast

Quote
john vanlandingham
You can learn Grant by asking "I wonder why Ford always put a bar from base of main hoop upwards when the rules don't require it?"

Well that settles it. The Ford guys OBVIOUSLY had engineered it and designed it and realized that without it EVERYONE would die and the rule makers were stupid for not requiring that single bar!

No Ford were bright enough to think beyond the rules about ROLLOVER protection for the occupants---which may possible never come into play---and think about shell stiffening and shell longevity..
The age does one passive thing--save your life, and one active thing, save the shell's life every time you pound it.

Grant you're arguing like a keyboard Honda hero.. You know 99% of people I've gently suggested that they might want to consider that little bar have kinda squinted, had a revalation (you can see it occuring, there's a skrunched look the their face goes calm and then a smile) and they say "Oh yeah I can see how that works, yeah!"

You mad, brah?

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Quote
danster

Quote
Josh Wimpey
No, a straight door-bar tube in a door opening strike with a tree is in tension immediately upon impact. ---Yet another reason to use the diagonals from the feet up to the strut towers both front and rear.

The curved outward tube is first in compression between the main hoop and front stay but has a tremendous amount of leverage due to the angles and moves over-center with very little resistance before coming into tension. And, once it come into tension, the twisting and deformation associated with coming over-center has weakened at least one element (the tube, or one of its connections, or connected tubes) and thus compromised the total tension load it can support before failure. This is why NASCAR bars are frowned upon and require a lot of additional tubing (mass & connections together) to be certified for US rally.

Straight bars (or at least all bars in a single plane between the main hoop and front stays) in the door opening... Please

You know that makes perfect sense. I can grasp the high leverage aspect and the resultant slack then needing taken up.
Straight bars as you describe are effectively in tension the whole length between the shock towers offering a pretty large area of support to absorb the force.
It's always good to hear different views as it helps to build the fuller picture and understanding.
And the good thing is no pipe bender is now required by me as a bonus!

EDIT, Blast! Well no pipe bender till Grant posted that pic!

really simple a straight door bar hitting a tree is in tension..
Straight beam is stronger than an arch, that's why bridges are always made without arches, right? wait



Simple.
Uh wait..


But but but!


Generally compression for a tube secured at the bottom like this II the force going V thataway..
And generally tension is for a tube like this secured at the bottom force going thisaway ^

doorbars being hit seems to me like its mainly perpendicular or nearly so, so bending force ----->ll seems the largest factor .
So an arch bent outwards has a shorter straight part, that's stronger. And the arched shape itself IS stronger---we've known that since pre-Roman times although they really went to town with arches, and the arched outward shape absorbs and disperses energy further away from the bodies in the car and that can't be bad...

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

I <3 the funicular shape machine.

---

Kirk Coughlin
Woodbury, MN and River Falls, WI

Quemadmodum gladius neminem occidit, occidentis telum est.