Opel GT chassis - 2 x 2 x .120" frame rail legal for 8.50?

[dave brode]

Gents,

I'm in the hacking/measuring/planning stage of building an Opel GT bracket car. Plans are to build a 10.0 car, no license or cert hassles, but you know how that goes.

I've never liked the store bought 2 x 3 x .083" wall frame rails. I like 1.625" round tube frames, but 2 x 2 x .120" square tubing is just so easy [and cheap] for a home builder. Would the 2 x 2 x .120 square tube pass NHRA & IHRA general rules if I decide to certify the car for <10.00 later?

Thanks.
Dave

[Alan Roehrich]

The thing to do is contact the NHRA Division 1 tech director, or at least one of the tech inspectors, Dave Ley for example.

I would not build a 2"x2" square tube chassis, even if they let me. I don't think it would have much value, and I'm not sure if I'd consider it suitable for the purpose. But that's just my opinion.

If you like 1-5/8" round tubing, why would you not build it out of that? It's not like a tubing bender would be a budget breaker, not if you're building a race car chassis. And a car properly built from 1-5/8" x 0.120" DOM would have a fair amount of value.

[dave brode]

Mr. Roehrich,

Gee, I'm red faced now. Not a bad thing, as 1.625' is really what I want, and I would no doubt regret the square tubing. I'll look into benders.

That said, you or anyone willing to cal'c the strength of 2 x 3 x .083" vs 2 x 2 x .120"? There are plenty of cars out there with store bought formed 2 x 3 x .083" frame rails [or chassis shop built]. That .083" has to get mighty thin on the bends.

Thanks.
Dave

[ijames]

The moment of inertia (determines stiffness) of 2x3x0.083" is 0.968 in^4 in the tall direction and 0.517 in^4 in the narrow direction, while 2x2x0.120" has a moment of inertia of 0.474 in^4. Once again, height trumps wall thickness . Oh, 1.625x0.120" round has a moment of inertia of 0.162 in^4. The yield strength is proportional to the section modulus, which is 0.645 and 0.517 in^3 for the 2x3, 0.474 in^3 for the 2x2, and 0.199 in^3 for the round tube.

[dave brode]

Interesting. Thank you, Sir.

[dave brode]

Gents,

Why would S&W Racecars recommend not using DOM tubing in a drag car roll cage? Like many many other chassis related companies, they offer ERW and CM. They will bend a DOM cage, but only in 1.75". http://www.swracecars.com/store/Opel-GT ... -1591.aspx

Their 25.4 chassis is offered in only ERW and 'moly. http://www.swracecars.com/store/opel-gt ... -1591.aspx

Thanks.
Dave