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Roll cage question


Mikedude32

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The material does not change the size / thickness requirements. The size thickness is controlled by the CCR and is dependant on the weight of the car.

 

Some rule books back in the day used to have different requirements for chrome-moly but I have not seen that in many many years, at least for road race sanctions.

 

Good luck,

Jeff

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Short answer is no, there is no distinction made in the rules for material spec between CM and mild steel. However, the tubing specs are determined by the weight of the car without fuel or driver. If that is under 3000 lb, the cage can be made of either 1.75 x 0.095 or 1.50 x 0.120 tubing. That spec also only applies to required bars per the rules; non-required bars can be made with thinner wall tubing.

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15.6.18 Roll Cage Tubing Sizes

For the purposes of determining roll bar tubing sizes, vehicle weight is as raced, but

without fuel and driver. Note: There is an allowance of minus 0.010 inches on all tubing

thicknesses. Minimum tubing size for the roll cage is:

Up to 1500 lbs.

1.375†x 0.095†Chrome-moly / Seamless mild steel (DOM)

1501 - 2200 lbs.

1.500†x 0.095†Chrome-moly / Seamless mild steel (DOM)

1.500†x 0.120†ERW* (No issuance of log books for cars with ERW cages 04/30/03)

*Note- Specifications listed for reference for inspection of grandfathered vehicles.

 

2201 - 3000 lbs.

1.500†x 0.120†Chrome-moly / Seamless mild steel (DOM)

1.750†x 0.095†Chrome-moly / Seamless mild steel (DOM)

1.750†x 0.120†ERW* (No issuance of log books for cars with ERW cages 04/30/03)

*Note- Specifications listed for reference for inspection of grandfathered vehicles.

3001 - 4000 lbs.

1.750†x .120†Chrome-moly / Seamless mild steel (DOM)

No ERW allowed.

Over 4000 lbs.2.000†x 0.120†Chrome-moly/Seamless mild steel (DOM)

No ERW allowed.

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Al hates it when I think about things, but there could be a safety concern here.

 

A 4th gen CAN get below 3000lbs. So, 1.75 ERW can be used. ERW is a LOT easier to find and a LOT cheaper to buy.

 

The rules are pretty vague, though.

 

I build a car that weighs 2975 with an ERW cage in it. All is wonderful.

 

Over time, I install a cool suit system, driver ventilation setup, brake ducts, passenger seat and harness setup and bigger fire suppression system.

 

Now, all of a sudden, the car weighs 3002 lbs w/o driver or fluids.

 

Am I allowed to remove all that stuff, including replacing the fire system with a 5lb handheld extinguisher so that I can pass a inspection?

 

Personally, I feel as though tubing dimensions should be based upon race weight and not necessarily a "conceived" weight.

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It's like being married ...

 

 

I build a car that weighs 2975 with 1.750†x 0.095 DOM cage in it.

OR

I find a car that has an ERW cage in it with a 4/29/03 log book.

 

All is wonderful.

 

Over time, I install a cool suit system, driver ventilation setup, brake ducts, passenger seat and harness setup and bigger fire suppression system.

 

Now, all of a sudden, the car weighs 3002 lbs w/o driver or fluids.

 

Am I allowed to remove all that stuff, including replacing the fire system with a 5lb handheld extinguisher so that I can pass a inspection?

 

Personally, I feel as though tubing dimensions should be based upon race weight and not necessarily a "conceived" weight.

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For the purposes of determining roll bar tubing sizes, vehicle weight is as raced, but without fuel and driver
So NO, you can't base the weight of the car "pre-build" as the criteria. If you add a cool suit, and it puts you over the weight limit "as raced", you're illegal.
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Personally, I feel as though tubing dimensions should be based upon race weight and not necessarily a "conceived" weight.

 

I thought the old Mitch was in hibernation?

 

Anyway, how often is this going to be an issue? When is the last time you pumped the tank bone dry just so someone could make sure you used the right tubing wall thickness?

 

Another item to point out, going with the thinner wall tubing is basically like a 50lb weight break (if your cage uses 100' of material), which is why I built my AI car with 1.5 x .120 DOM. In hindsight, I'd probably do 1.75 x .095 DOM, but it's a done deal now.

 

For a data point:

-1.75 x .120 DOM is ~2.1lb/ft

-1.50 x .120 DOM is ~1.6lb/ft

-1.75 x .095 DOM is ~1.6lb/ft.

 

So, if you use the thinner wall thickness, you're adding the ability install all those "upgrades".

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When is the last time you pumped the tank bone dry just so someone could make sure you used the right tubing wall thickness?
That's the thing - you don't have to pump the tank dry. The rule states "as raced" - meaning as it comes off the track. Warts and all.
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Except that if you come off the track at 3050 without the driver and you have 51 pounds of fuel in the car, it's still legal. Realistically, this is only going to be an issue when a car is new and getting it's first log book. You could be required to show it meets the weight requirement and you might have drain the tank to prove it.

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That's the thing - you don't have to pump the tank dry. The rule states "as raced" - meaning as it comes off the track. Warts and all.

 

15.6.18 Roll Cage Tubing Sizes

For the purposes of determining roll bar tubing sizes, vehicle weight is as raced, but

without fuel and driver.

 

looks to me you have to pump the tank dry.

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Nope TJ ... still here!

 

The whole point of my question was to bring to the surface the weight breaks points and potential consequences as your car "ages".

 

Today you build a car that just gets in under the break point. But next season, changing the exhaust, adding creature comforts, changing to a larger radiator, changing wheels ... a whole multitude of stuff could very well put an owner outside the weight break.

 

An owner can inadvertently make his cage illegal. I realize that it is the owner's responsibility to track that sort of thing. But as I recall, this series is considered a hobbyist series. Hobbyists might not have the same level of awareness or attention to detail that Brad or Matt might have.

 

The "without driver and fuel" caveat should be revised and align itself with post race weight minimums. After all, that is the weight we are building a cage for, correct?

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Anyway, how often is this going to be an issue? When is the last time you pumped the tank bone dry just so someone could make sure you used the right tubing wall thickness?

 

Another item to point out, going with the thinner wall tubing is basically like a 50lb weight break (if your cage uses 100' of material), which is why I built my AI car with 1.5 x .120 DOM. In hindsight, I'd probably do 1.75 x .095 DOM, but it's a done deal now.

 

For a data point:

-1.75 x .120 DOM is ~2.1lb/ft

-1.50 x .120 DOM is ~1.6lb/ft

-1.75 x .095 DOM is ~1.6lb/ft.

 

So, if you use the thinner wall thickness, you're adding the ability install all those "upgrades".

 

With the average CMC car, just how much cage do we have? 100 seems to be way more than I can picture without actually getting the car out of the trailer to measure only to save 50# when done with a weaker cage.

I don't see the need to use smaller or thinner walled material for a few pounds of weight savings.

Safety is paramount, use the 1.75 x .120 DOM and be done with it for the size of our cars IMO.

 

I don't have to have a fire system, but I do.

I don't have to have a HANS, but I do.

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It's probably closer to 140 feet, depending on how the cage is built and what extra bars you might have. Have you done any FEA analysis on cage structures, or are you just assuming that more weight is better? More lighter, thinner tubes properly placed can be a lot stronger and safer than a marginally designed cage with fewer, thicker tubes. The fact that it will probably also be lighter is merely a side benefit.

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With the average CMC car, just how much cage do we have? 100 seems to be way more than I can picture without actually getting the car out of the trailer to measure only to save 50# when done with a weaker cage.

I don't see the need to use smaller or thinner walled material for a few pounds of weight savings.

Safety is paramount, use the 1.75 x .120 DOM and be done with it for the size of our cars IMO.

 

I don't have to have a fire system, but I do.

I don't have to have a HANS, but I do.

 

The average cage uses more then 100', only do cages that meet bare bones specs (only 2 driver DBs, 1 pass DB, no bars to firewall, 1 back stay diagonal) usually use less.

 

It's all based on driver comfort level. I feel safe with 1.5 x .120 surrounding me and it gives me a nice weight break. I'd do it again for weight, especially if I was building a CMC 4th gen.

 

I race with about the minimum amount of safety equipment (no HANS, no fire system) because then I'm not sitting at home saving for the next item, but the safety equipment I do have is good quality (Sparco suit, 10lb extinguisher) and I trust it to protect me. My $.02, FWIW.

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I have built at least 7 cages in CMC cars all with the required bars and have never used over 90 feet.

Use the 1.75/120 DOM, then you are good to go.

Also if you don't have a HANS or similar, that should be your very next purchase before you get back into a race car.

Thanks,

Tony Guaglione

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i'm w/ Tony. we started our 5th or 6th cage today, and we normally use 70' for a normal cage. the exception was the 3rd gen we just done. 115' - it had 3 row NASCAR door bars on BOTH sides. the car saved 46# w/ .095" over the same cage using .120".

i agree, .120" is the way most us us should build our cages. .095" if you have some knowlege in what your doing.

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Nape... you really should get the hans. The fire system is not 'as' critical... but the Hans is something you will take with you forever...

 

I know it's tough spending $800+ on something that doesn't make you go fast... but it will suck worse if you aren't able to 'drive' to go fast ever again!

 

We've all heard stories of bad wrecks with people wearing HANS devices... and them walking away.

 

I'm know HANS dealer... but I'd recommend if you are Road Racing... (Not Track Daying)... you should have one!

 

As for Cage Thickness... I think it's important to also consider what other sanctions allow... you don't want to build a purpose built CMC car, and never be able to take it SCCA Racing (or sell it to someone who may want to... then it is worthless to anyone but you).

 

My .02

 

Dave

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I agree with Dave on the HANS. I sat out a couple events until I could afford one and am really glad I did. My family and friends are too.

 

As far as cages, the last time I checked NASA and SCCA had virtually the same thickness requirements - that could have changed though so check.

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Have you done any FEA analysis on cage structures, or are you just assuming that more weight is better? More lighter, thinner tubes properly placed can be a lot stronger and safer than a marginally designed cage with fewer, thicker tubes. The fact that it will probably also be lighter is merely a side benefit.

 

You are contradicting yourself on using more of the smaller to make it stronger then it could weigh as much weight as a bare bones thicker cage. That aside, you missed my point. And no I haven't done any analysis but the assumption was the exact same cage, one thinner and the other thicker, the thicker would be stronger. Again, both being built the same.

He never mentioned building a thinner cage with better design or a thicker cage with a worse design. It was a given it was the same design.

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