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I'm going to take a shot at significantly stiffening my chassis by installing metal bars along the frame rails, with an X in between.

Does anyone have any experience doing this? I need an idea for clearing the exhaust... and I'm not sure exactly what to weld to. Any suggestions on steel thickness?

Cjthor, and I were thinking about doing this. We were think more of welding in nuts, though.

Instead of just welding in nuts, you would either weld or bolt on metal to the frame rails themselves to support them first, then have x members go between the two pieces, like the miata braces. This will help our weak frame rails and prevent them from getting dented from jacks.

See those things on Flyin' Miata? Make those for the MX-3!

onlytrueromeo wrote:Instead of just welding in nuts, you would either weld or bolt on metal to the frame rails themselves to support them first, then have x members go between the two pieces, like the miata braces. This will help our weak frame rails and prevent them from getting dented from jacks.

I was thinking that, exactly. My frame rails are all chewed up as it is.

Is that the best place to weld a strip of metal? I was thinking something 6' long from wheel well to wheel well, on the inside of the frame rail. Maybe 1/4" thick by 5/8" tall. Then bolting or welding beams across in an X to each end, and possibly two more at each end horizontally across the car.

If you guys go through with this, I want to see the results, and I hope you make diagrams with dimensions!

tehbrookzorz wrote:If you guys go through with this, I want to see the results, and I hope you make diagrams with dimensions!

Will do.

Very interesting project! Keep us posted, I might try to put some thought into this also this spring.

1/4" is pretty thick. I'd visit a few metal fab shops as they would have a better idea regarding material thickness vers weight. I though adding a roll cage to the inside was a good way to stiffen up a cars frame.

Well it's a daily driver.. Roll cage might be a little excessive. :p

Right now I'm thinking 1/4" square hot rolled steel angle beams (0.75" x 0.75") running inside of the rails, welded all along, and to the bottom. I'll weld 1/2" thick steel blocks to each end, and drill out holes to mount the X beams and horizontal beams. Then I'll find put a bolt in the middle of the X to tie the system together.

The X and horizontal beams could be aluminum for weight savings. They should experience mainly tensile force under loading if what I'm thinking about chassis dynamics is correct. Which it probably isn't.

Well, they wouldn't all be experiencing tensile forces otherwise your car would be trying to rip itself apart

One would be under tension, while the other is being compressed. The more "webbed" you make the design the better, as you will eliminate point loads. The miata one got it right - it distributes the load well and should not crack from use too soon.

onlytrueromeo wrote:Well, they wouldn't all be experiencing tensile forces otherwise your car would be trying to rip itself apart

One would be under tension, while the other is being compressed. The more "webbed" you make the design the better, as you will eliminate point loads. The miata one got it right - it distributes the load well and should not crack from use too soon.

Well imagine one corner of the car is compressed upwards over a bump. That should stretch the X beam from that corner to the opposite corner, as well as the horizontal beam on that corner, while trying to bend the frame rail. Lifting action on the front of the car should stretch the X, while trying to bend the frame rails. The only time they should experience compressive force is when jacking up the car, no?

Any time you "twist" a "frame" there will be tension, compression, and torsion.

onlytrueromeo wrote:Any time you "twist" a "frame" there will be tension, compression, and torsion.

On the frame, sure... but on the frame reinforcement? Where would the compression be, assuming you hit a bump with the front left wheel?

I know nothing about this stuff so help me get this right before I start welding.

I'm not very good at drawing, so bear with me. I will try to upload a sketch (in 2d) of what this would look like. I don't have my 3d modeling software on this computer.