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This is a really poor drawing. I probably should have done better I will not go into all the science of it by writing equations and explaining exactly what the stresses will be because it depends on lengths and forces. This is just a very basic description.

Hmm..

Well, the frame reinforcement is actually below the page, right? So if there's an upwards force F, there should only be a bending effect (shearing?) or tension on the top and left lines, right? No effect on the unlabelled X beam, and a tension effect on the one you indicated.

For a downward force F, there should be a compression on that X beam. But, downward forces shouldn't exist, in theory, since the maximum loading is the force of gravity (+/- a bit under hard cornering). The main multi-G stresses should be from bumps/broken roads and should always be forcing upwards.

Well that is a drawing of the frame reinforcement. It would attach right to the frame of the car (top and bottom lines) and become one with it - assuming all points are equally supported w/ adequate welds or bolts.

Yes all the initial forces would be UP (bumps) but when cornering hard the frame is twisting very differently then it is when you are driving in a straight line. The frame will bend DOWN on the outside of the corner. Those members are not zero force members in every circumstance.

Hmm, yeah I guess the main purpose of this is to improve cornering stability..

Ok, what materials would you suggest? I'd like to stick with low-carbon steel (A36) for ease of welding. Do you think it would be strong enough?

Would there be a corrosive effect if I tried to weld aluminum to the frame?

Carbon steel will rush pretty quickly being exposed to all the elements unless you paint it very well. There will be no movement so you should not have to worry about anything wearing. You will also not want something brittle+hard as we would want more of an elastic deformation to occur rather than plastic so that we would not see stress cracks.

http://www.flyinmiata.com/index.php?dep ... %201990-97" onclick="window.open(this.href);return false;

Trust the experts! Stainless steel would be the best because of the non-corrosive nature of it, but regular A36 carbon steel would probably work too, assuming you will be priming+painting everything afterwards and maybe even adding a rubber coating to it. If you weld everything, you will have a hard time removing the exhaust in the future, but it will make construction alot cheaper! Do not use round beams as in rebar because they are only good in tension applications and concrete reinforcement. Get something w/ an I shape or flat or HHS would be nice if they make them small - I've only dealt with stuff for designing buildings/bridges in class. You want it to be able to handle tension/compression and bending applied to the center of it. (transverse loads). This is why a "webbed" design like the miata one is nice! Not that you'd be jacking the car from the center of the brace, but it is good to know which way and how beams will deflect. A round beam will deflect any which way, but a differently shaped beam should only deflect along its weak axis.

onlytrueromeo wrote:Carbon steel will rush pretty quickly being exposed to all the elements unless you paint it very well. There will be no movement so you should not have to worry about anything wearing. You will also not want something brittle+hard as we would want more of an elastic deformation to occur rather than plastic so that we would not see stress cracks.

http://www.flyinmiata.com/index.php?dep ... %201990-97" onclick="window.open(this.href);return false;

Trust the experts! Stainless steel would be the best because of the non-corrosive nature of it, but regular A36 carbon steel would probably work too, assuming you will be priming+painting everything afterwards and maybe even adding a rubber coating to it. If you weld everything, you will have a hard time removing the exhaust in the future, but it will make construction alot cheaper! Do not use round beams as in rebar because they are only good in tension applications and concrete reinforcement. Get something w/ an I shape or flat or HHS would be nice if they make them small - I've only dealt with stuff for designing buildings/bridges in class. You want it to be able to handle tension/compression and bending applied to the center of it. (transverse loads). This is why a "webbed" design like the miata one is nice! Not that you'd be jacking the car from the center of the brace, but it is good to know which way and how beams will deflect. A round beam will deflect any which way, but a differently shaped beam should only deflect along its weak axis.

Well, the Miata reinforcement is beautiful but that webbed design is way beyond my capabilities.

I was considering 316 stainless, but that stuff is so expensive. My materials cost would rise from $75 shipped to probably $500. :/

I was planning to coat the entire setup in rubberized asphalt and keep an eye on it whenever I'm under the car. Even with a little rust, those beams would be so big and thick, I'm sure even without adequate coating they'd last the 5 or so years I've got left on this car..

I'll definitely bolt the X and horizontal bars to the frame rail reinforcements so they can be removed easily.

Anyway, I'll give it some more thought. Thanks for all your help. I'll keep you posted.

Ya, I wouldn't think stainless would be an option for most of us!

Good good on bolting to the frame. Make sure all your cross supports are welded to each other (like in the frame example if you have an X, weld at the crossing of the two) This will make the effective length of each member shorter and provide a stronger brace rather than if you just overlapped the two. You can also cut + weld them so you only have 1 layer of metal. I'm probably not explaining this very well

Good luck! Definitely Take pictures!

onlytrueromeo wrote:Ya, I wouldn't think stainless would be an option for most of us!

Good good on bolting to the frame. Make sure all your cross supports are welded to each other (like in the frame example if you have an X, weld at the crossing of the two) This will make the effective length of each member shorter and provide a stronger brace rather than if you just overlapped the two. You can also cut + weld them so you only have 1 layer of metal. I'm probably not explaining this very well

Good luck! Definitely Take pictures!

I was planning to bolt the X beams in the middle, and possibly to another reinforcement welded/bolted to the center of the car if I can find a beam there. Could weld the X beams, but it wouldn't be as strong as a bolt since I'd have to edge or butt weld it over a short length.

Most definitely I'll take pics along the way and document all the materials/angles/lengths. If it works out I'm sure others would be interested in trying it.

If you can weld well, it'd be just as strong since drilling a hole for a bolt removes material and make that spot a weak point in the beam.

Honestly though, if you do it right it should not matter either way.

I bought my first welder 3 days ago.

Would a roll cage stiffen things up similar to the underbody reinforcement?

^Yes but in a different way. Roll cage strengthens body more than the frame, but it still strengths the frame somewhat. This is just for the frame. I would love to to both! Then you'd have a SOLID platform w/ no chassis flex!

Why kill it when you can overkill it?

No such thing as overkill w/ car work

My concern with overkill in this case would be extra weight. If you were wanting to go that far, you could strip the car down, and seam weld all the spot welded stuff, and add reinforcements in corners, and such. That would keep the weight down, and significantly strengthen the chassis (I think more than an underbody brace). If I were building a race only car, I would do that, and connect the strut towers to the B-pillars with an "X", at the base of a B-pillar bar. You could rally race it.