The original and the best frame rail reinforcements for the Miata.
First, why do you want chassis rigidity? Because a stiff structure allows the suspension to work better. If your chassis flexes, it's basically a big undamped spring that changes your suspension geometry under load and shudders every time you hit a bump. A stiff chassis will give your suspension a solid platform to work from, leading to better, more predictable handling as well as improved ride quality. There really is no downside. Chassis stiffness is usually measured as torsional rigidity - resistance to twist - because that's how loads usually travel through a car.
These braces slide over the factory frame rails and stiffen the car dramatically. The factory rails are easily damaged over bumps and mistakes when jacking, and every time they are bent the car gets floppier. When we tested these on a 2002 - the stiffest Miata that Mazda ever made without additional bracing - we saw chassis stiffness improve by 17.5%.
Ground clearance is unaffected and the total added weight to the car is 13.5 lbs. The rails and the fasteners are 14 gauge stainless steel to prevent corrosion. They're strong enough to act as jacking points as well.
There have been multiple running changes to these since we first developed them in 2005. The big news for the version 2.0 set - the ones with Flyin' Miata cut through the sides - is compatibility with the latest generation of butterfly brace. They're also compatible with our older butterfly brace designs.
To make your Miata even stiffer, we highly recommend our butterfly brace. You can either get the full butterfly which includes frame rails, or you can add the butterfly portion later.
No welding is required for installation although 24 holes need to be drilled in the car. Fits all 1990-2000 cars as well as the 2001-02 cars without the Sport bracing. Sport cars and 2003-05 Miatas can use the braces although one of the factory cross bars has to be removed. The factory bar can be retained with a slight modification. If your factory rails have been damaged, they may need some massaging with a hammer to allow these to slip over top.
There are less expensive knock-offs out there. None have all the features of our originals, though, such as stainless steel construction and the cutouts for lower weight. Also, the FM rails are the only ones compatible with the acclaimed butterfly brace upgrade.
Miatas are naturally the only thing we can guarantee fitment on. If you'd like to try them on a different car, the cross-section of the frame rails can't be bigger than 2.65" x 1.875". Our rails are 43" long (longest dimension).
See an installation! One note about this video - the competitor product mentioned is made of mild steel with zinc coated fasteners so it'll be less corrosion resistant than our stainless items. Also, these rails survived multiple end-over-end rollovers on a previous car, then got reused.