What bar/tube thickness would you recommend?

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SaltyAppointment@reddit

Most people on reddit just bolt stuff on. Fab some aero part/brackets at best. Your question isn't for an average redditor. They should be determined by an engineer. It takes a lot of research. The material you seek would most likely be chrome moly. Sizing, thickness of the tubes would depend on the location and what it's supporting. A smart engineer wouldn't build the whole thing with just one tube sizing.

Also, I can't imagine you'd put yourself in a situation where you'd can crash at 150 mph.

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Big-Pomelo7619@reddit (OP)

Now this is some good insight. Don't worry, I know what I'm doing, plus I got other certified ppl to help me. We already know some of the materials and their dimensions that we're gonna use. It's not official, but I was planning to use a 765LT's carbon monocoque for part of it, along with other carbon parts. I just wanted to see what others would say if I asked this question.

Although I don't plan to crash, it's just a "what if" situation.

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SaltyAppointment@reddit

I'd definitely start with a chassis that's already made instead of building one from scratch. It's definitely a lot less headache. Unless you over design it, safety concern would constantly be in the back of my head. With a new chassis, you'd need a 3D model to do finite element analysis. Throw the body in a wind tunnel to test for airflow into and around the car. Also, don't forget you'd fab a body from scratch to fit the tube chassis. If you get a premade chassis, all of that is done for you. You can even get a kit car/supercar (I currently have one). You'd still get to be involved in everything (except building the chassis).

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Public_Enemy_No2@reddit

How old are you?

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Big-Pomelo7619@reddit (OP)

Old enough to know the answer to my question since I just wanted to see what people would say.

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Public_Enemy_No2@reddit

👌🏽

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Big-Pomelo7619@reddit (OP)

Well thanks for the insights people, I'm actually quite certified in this stuff and I have other certified people working with me on these projects. I just wanted others to share their insight/opinion about stuff like this.

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Carbonbuildup@reddit

Certified how? In what? I have been building cars for 20 years for various sanctioning bodies and your question is that of a 15 year old. If you’re attempting 200mph there’s really only one place on earth you can do that and that’s the Boneville salt flats. They have a comprehensive rule book that outlines everything you need to do to meet class regulations to run 200mph. A 1200 lb car running a turbo bike motor with the goal of 180-200mph is built completely differently than an LS powered 3200lb car with the intention of running the same speeds. Please don’t reply that you’re building a street car to do this because there’s numerous reasons why that’s just fucking stupid.

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Big-Pomelo7619@reddit (OP)

BSc in Mech E. Automotive Service Center Management lvl 4 (Motor vehicle repairs lvl 4 included in this). and a bunch of other stuff related to the automotive field.

In my country, there are a few places where cars are just barely capable of reaching 200 on the highways. I should know seeing that I have been at that speed on those highways many times before.

It's not one of those builds where you stay at 200 for a long time, it would just have the capability to reach that speed, even if only 190. It should just be able to fit the minimum requirement of sitting comfortably at 170.

I've been building and fixing cars for over 19 years, and the people helping me for some 20+ years and others for 30+ years.

However, It's not actually supposed to be a street car but within my country's extreme limits, it can be used on the street. It was intended to have the ability of the shell being transferred over to the slower build. So technically, not the same car. One frame is built for the street, the other for non-street purposes on the tracks we have here.

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SameCharacter3619@reddit

Oh, so from what I understand. The one you're talking about now is for drag-related purposes, but you have another one being built for street use, and you would just switch the shell/cover between them. Interesting. Just don't get yourself killed.

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Big-Pomelo7619@reddit (OP)

Yes that's exactly it. 1 frame for drag, the other for street, just using the same shell.

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Satanslittlewizard@reddit

“Certified” - but asking nonsensical technical questions on Reddit. Seems right.

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BrentRussel@reddit

Dallara makes the DW12 (current Indycar chassis) out of carbon fiber and Kevlar, and those things go like 240 MPH. There's a Dallara factory with a showroom in Indianapolis. You could probably see one there and mimic the design. Try not to kill yourself once you get it built.

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Big-Pomelo7619@reddit (OP)

Thanks. No worries, got a full certified team helping. It's just something capable of reaching that speed, and technically just for drag. The other one being built rn uses the same shell that this one would, but for street use.

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SausagegFingers@reddit

you need to do a lot of research to build a car like that. you're not making a tube chassis out of carbon, and aluminium would be a bad idea. High level cars tend to use T45 / cromoly, seamless mild steel is fine too just has to be thicker to compensate.

Go spend a lot of time looking at what other people do, and look into roll cage specs for a start

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Big-Pomelo7619@reddit (OP)

Thanks a lot. I've been doing research on it for like 8 years now. I even went and got a BSc. in Mechanical Engineering because I like doing these stuff. I forgot to mention that I was, not sure yet, but planning to use a 675LT carbon monocoque that I am acquiring to build it, but I just wanted to get people's opinion on what they would recommend so I can adjust based on that.

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greycar@reddit

You may wish to revisit your statics and solids textbooks. Those are the bare minimum to take an educated guess at sizing members. You should also look to any racing rules or roll cage rules you can find for allowable defection, resistance factors, and amplification factors for force and deflection. Other things to consider is connection resistance, weld design, slenderness ratio, and doing a p-delta analysis on your load cases.

If you don't want to do these things then draft up your frame skeleton and work with a structural consultant who specializes in FEA.

Source: I'm a Professional Mechanical Engineer who used to do Automotive Research.

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Big-Pomelo7619@reddit (OP)

Those factors are also included in the whole thing. There's a whole certified team assisting me with this.

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Big-Pomelo7619@reddit (OP)

It's not officially intended to reach 200, just like 180-ish. I intend to add the full works, airbags, abs, the full workup, like a typical supercar. Basically like a car from the factory, but built in a workshop by me (and a few other certified people).

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MaybeVladimirPutinJr@reddit

Adding airbags to a custon car will be near impossible. They have an extremely short window of time to operate correctly or else they will injure you worse.

What's the plan for when your chassis geometry is slightly out of whack and it becomes unsettled at 180mph?

I don't think this is the kind of project you jump right into. I'd start with something slower and cheaper like building your own version of an exocet or ariel atom as a learning experience before trying to rival modern supercars.

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GoldfishDude@reddit

Go buy a DF Goblin kit and stop this

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ultramilkplus@reddit

What sanctioning body? They'll have a rule book.

Beyond that, find a car that does what you're doing and see if you can get an idea of the materials used, then tweak it. Howe racing built/builds the Trans Am chassis and you may be able crib some material sizes and ideas off those. As far as crashing goes, if you hit something over 60mph, you're dead (production cars can barely manage 50mph) but if you follow the rules from someone like NHRA/ECTA/SCCA/FIA/etc. you might survive a rollover/wall scrape. That'd involve nets, containment seat, cage, fire suppression, etc.

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MeltingEarbuds@reddit

You're goofy as hell kid for thinking "material thickness" will save your dumbass at 200mph

Look up carbon monocoque and get an engineering degree if you want to stand any chance at living through that.

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Crazy83519@reddit

This certainly feels like a "if you have to ask, you probably shouldn't" type of question.

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Big-Pomelo7619@reddit (OP)

How so? It's something I intend to do overtime. I'm already in the process of building one that can reach about 100 out of 1/8" steel tubes so I just wanna know that frame thickness and material anyone would recommend for the other one that's gonna go way faster.

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mittenfists@reddit

Because there isn't a single answer. The engineering determines the material needs for the associated stresses.

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mshuler@reddit

and specifications! Every race series out there has cage specs based on detailed drawings, speeds achievable, weight, class goals (ie "street" vs full race car). OP should check with the race series tech team for proper cage documentation on optional materials, size, design, placement, optional bars, and on and on. OP should build to the race spec intended to be raced in. Period. Even crapcan 24 hours of lemons cars have requirements and clear docs (which btw are outstanding as a starting point, if nothing else).

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