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Old 01-05-2015, 11:56 PM   #1
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Roll cage material?

Hi All,

I am in the process of building a roll cage into my Fiat Uno. I have read a lot of mixed opinions on the web as to what material to use? Chomoly or Mild Steel? Please let me know your experiences/opinions on the two options?
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Old 01-06-2015, 02:37 AM   #2
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Cro-Mo is significantly lighter, but also more expensive. After checking the budget, I'd figure out how close the car is to the minimum weight for its class.
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Old 01-06-2015, 03:06 AM   #3
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Chromoly will only save seight if it allows you to use thinner wall tubing, the material it's self weighs the same. If you have any doubts about your welding abilities, 1018 DOM steel is more forgiving. 4130 is prone to brittleness in the HAZ if welded with excessive heat. Do some Google searches on the subject.
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Old 01-06-2015, 06:04 AM   #4
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First, do not skimp on a roll cage! Do you really want the "minimum" strength protecting you in a crash? Do you really want a cage built to a "budget"?

If you are in a driving situation where you need a cage, then you are in a situation where the driving is somewhat uncontrolled as compared to how HPDE's are conducted. This brings a completely new level of danger into the mix.

Take a look at these photos from a Boxster roll-over at Willow Springs. This was the result of minor contact between two cars coming out of Turn 2 at around 85mph. This car was the innocent driver - he was tapped in the rear, spun off track, caught in the dirt, and rolled 5+ times. It doesn't happen often but it can happen and a cage is there for exactly that worst case scenario.

Most cage builders at this time (2012) thought that the cages they were building were more than adequate - but the pictures tell a different story...






The cage in my car is one of the most stout and well built around. I know, that is quite a claim to make. Yes, its heavy and I have had to reduce weight in other places to account for the additional cage weight as compared to other Spec Boxster's with lighter cages.

People ask me: Is it heavier than it needs to be? Well, that depends on your definition of how strong a cage needs to be to keep you alive. There are no specifications that say build to this exact level and you are guaranteed to walk away unharmed. You build your cage and take your chances.

In my case, I wanted to maximize, not minimize, my cage to ensure that I had a higher probability that I would be able to walk away from totaling the car. I have a high paying job, a wife, and kids who fully expect me to come home from every race healthy.

So, what is your expectation? Is being disabled ok? Brain damaged ok?

I don't mean to be dramatic and get on my soapbox but this is the reality of the consequences of the decisions that you are making.

Take some time and think through what you want from your cage and communicate that to the cage designer and builder and then pay whatever it costs. Your life will literally depend on it.

I'll post the exact spec's of the tubing later today (don't have them memorized).

Here are some pic's of the cage in my Spec Boxster before paint:







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Last edited by thstone; 01-06-2015 at 06:14 AM.
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Old 01-06-2015, 07:56 AM   #5
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And

Get someone who has done it before in a Boxster, don't let this be your first design or welding experience. If you have rolled before, you don't have to ask why.
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Old 01-07-2015, 08:29 PM   #6
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As promised, here are the technical spec's for my roll cage;
  • 1.75" tube diameter
  • 0.095" tube wall thickness
  • 4130 alloy chromolly steel
  • Tig welded joints with 70S rod (specialty for 4130 welding)
  • 6-point style cage
  • Sheet metal gussets in critical areas
  • Custom driver's side door bars increase strength compared to standard NASCAR style
  • Large area base plates mig welded to structural areas of the chassis
  • "A" pillar vertical tubes (aka FIA bar)
  • Windshield frame bar, door bars, and main hoop are all stich welded to the chassis for increased rigidity
  • "Knee bar" and steering column mounts to replace factory dash bar
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Old 05-20-2015, 09:21 AM   #7
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Tom--

Who built your cage?

I'm getting mine built by Josh Lucas at Lucas Fabrication in Huntington Beach.

I like the features you've put into your cage. If you also used Josh, then I could just tell him, "Do it just like Tom's cage".

Thanks,

Greg
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Old 05-20-2015, 11:03 AM   #8
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Quote:
Originally Posted by thstone View Post
First, do not skimp on a roll cage! Do you really want the "minimum" strength protecting you in a crash? Do you really want a cage built to a "budget"?

Take a look at these photos from a Boxster roll-over at Willow Springs. This was the result of minor contact between two cars coming out of Turn 2 at around 85mph. This car was the innocent driver - he was tapped in the rear, spun off track, caught in the dirt, and rolled 5+ times. It doesn't happen often but it can happen and a cage is there for exactly that worst case scenario.

Most cage builders at this time (2012) thought that the cages they were building were more than adequate - but the pictures tell a different story...

I'll post the exact spec's of the tubing later today (don't have them memorized).
Thstone:

I clearly remember the video of the crash, it's pretty impressive...!

Edit: this is the link.. https://youtu.be/MIjNa4XjbLE




.

Last edited by Gilles; 05-20-2015 at 11:11 AM.
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Old 05-20-2015, 02:23 PM   #9
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Roll cage 101

There's a good article in Velocity magazine (magazine of the socal Porsche Owner's Club) on roll cages in issue 57-2, May 2012. It's called "Rollcage 101", by Jim Pierce, on page 12.

Here's a link to the issue:

https://porscheclubracing.org/wp-content/uploads/2012/09/VELOCITY-57-2.pdf
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Old 05-22-2015, 10:21 AM   #10
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Quote:
Originally Posted by Greg Holmberg View Post
Tom--

Who built your cage?

I'm getting mine built by Josh Lucas at Lucas Fabrication in Huntington Beach.

I like the features you've put into your cage. If you also used Josh, then I could just tell him, "Do it just like Tom's cage".

Thanks,

Greg
Yes, it was built by Josh. One of the best.
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