Determining correct cage tubing size

[keycom]

Trying to determine the correct minimum weight to figure out the correct minimum tubing size I can use for an 86 VW Scirocco.
Minimum weight is 2,320 (ITA-h, page 332 of GCR).

Page 89, 9.4.1.F.3 says the tubing should be 1.5" x .120" DOM.

But page 89, 9.4.1.F.2 just above it lists the weights as "WITHOUT DRIVER".

Is this true for IT cars also?

There is a significant price difference if I can drop to .095" DOM.

Thanks for your input.

[Greg Amy]

For Improved Touring cars, you're allowed to use the tubing appropriate for your car's minimum race weight, minus 180 pounds.

The ITA 1986 Scirocco has a min weight of 2320; subtract 180 pounds (as per GCR 9.4.1.F.4) and you can build your cage to specs appropriate to a vehicle weight of 2140#.

On Edit: HOWEVER, you should seriously consider building your rollcage to the next higher weight class. If sometime in the future your car were to be re-classified to ITB (which, historically, is a very distinct possibility), you'd be forced to completely rebuild the cage to be legal. It's possible the car could get a waiver, but this has been a sticking point for re-classifying slower cars into slower classes (e.g., first-gen RX-7 into ITB).

Besides, how much total weight and cost are we really talking about here...? In the long run, it's insignificant.

[joeg]

It's page 322?

GCR P.89 (4): "Improved Touring roll cage tubing sizes are to be calculated based on the published vehicle weight minus 180 lbs."

Accordingly, you are at 2140 lbs. which is good for .095 wall.

.120 wall is "safer," however, IMHO.

[John Herman]

how much totall weight and cost are we really talking about here...?
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34.4# assuming 100' of tubing. A good compromise would be to make the required tubes out of 0.120 and any optional braces (or tubes which could easily be replaced later) out of 0.095.

[keycom]

It's page 322?

GCR P.89 (4): "Improved Touring roll cage tubing sizes are to be calculated based on the published vehicle weight minus 180 lbs."

Accordingly, you are at 2140 lbs. which is good for .095 wall.

.120 wall is "safer," however, IMHO.
[/b]

THANKS!

Geez, I don't know how I miss some of this stuff that is clearly in the book. :018:

Comments about using the next size larger tubing have been duly noted. Good points!

[tom_sprecher]

FWIW: 1.75" x .095 is .1# per foot lighter that 1.5" x .120" wall. I used all 1.75" and used .120" on the main hoop and .095" everywhere else and would bet it's lighter and much stronger than an all .120" x 1.5" cage. Plus, it's what I had to work with which always makes a decision easier.

[Speed Raycer]

1.75x.095 wins hands down compared to 1.5x.095 UNLESS you're building something with a small cabin (like a miata). You can drop a little of the overall weight by using some thinner walled tube here and there on non-required bars, just don't get stupid thin or small. Remember, cages are supposed to protect ;)

[Bill Miller]

I agree w/ Tom, I'd use 1.75 x .095 over 1.5 x .120, it's stronger.


Tom,

I thought I read something that all the required tubes had to be the same size?

[keycom]

You can drop a little of the overall weight by using some thinner walled tube here and there on non-required bars,
[/b]

[tom_sprecher]

I thought I read something that all the required tubes had to be the same size?
[/b]

I could not find anything to confirm. Only that you had 3 choices in the 2201-3000# range.