NA/NB Flat Underbody
NA/NB Miata Flat Underbody Group Buy
For years we have been offering multiple Rear Diffuser models for NA and NB Miatas. Now we’re pleased to announce that we will be offering Flat Underbody systems that are compatible with our Rear Diffuser kits!
WHAT IS A FLAT UNDERBODY AND WHY WOULD I NEED ONE?
If you look under a pre-2010 car, it’s very rare that you would find one equipped with a Flat Underbody from the factory. But now a days many manufacturers are finding benefits to Flat Underbodies and are starting to put them on most modern Sports Cars and sometimes even family cars. Some of the benefits to having a Flat Underbody are_
Less drag resulting in less fuel consumption
Less drag leading to better acceleration and/or top speed (depending on other vehicle factors)
Reduced aerodynamic lift
The idea behind a flat floor is to create a smooth surface for air to travel along. This is done is by attaching a flat panel to the bottom of the car to cover up the frame, driveline components, exhaust components, and anything else that would create drag and turbulence.
HOW DOES THE R THEORY FLAT UNDERBODY WORK?
When designing our Flat Underbody system we had a few design criteria in mind_
It has to be light weight.
Must be compatible with all our Rear Diffusers and as many other Aftermarket Frame Stiffeners as possible.
Since it has to cover almost the entire underbody of the car, it can’t cost a million bucks to ship.
Has to have minimal exposed hardware components so that the surface is as clean as possible.
To cover all criteria we designed the Flat Underbody to be modular while reducing the amount of exposed hardware pieces. We reduced the amount of exposed hardware pieces by using hardware already used by our Frame Rail Braces. This means the Flat Underbody does not need any additional rails to mount to. For the most part you can bolt them right in if you already have our Frame Rail Braces. They will also fit other aftermarket Frame Rail braces with some modification. We slotted the holes to increase the likely-hood of fitting other braces. But hole position might vary beyond the slotted holes with other Frame Rail Braces, so re-drilling the holes may or may not be required. It’s aluminum so it’s not a hard modification to make!
The rear section of the Flat Underbody is designed to bolt to pre-existing mounts on the 94-05 Rear Subframe.
*FITMENT NOTES* - PLEASE READ
The rear section will fit 90-93 cars if you have a later model year subframe, or if you welded aftermarket subframe tabs to accept the OEM Mazda Ladder Brace.
It will not fit the later NB2 brace that has the double cross brace. You will have to either swap to an earlier brace that has the single cross or modify your brace to get rid of the obtrusive cross section that hangs low.
The Flat Underbody might bolt to Frame Rail Braces from other companies. You may or may not be required to redrill holes on the Flat Underbody for the holes to line up with other competitor Braces. If you are in any doubt about fitment, feel free to email us.
You can bolt the Flat Underbody onto a Miata that does not have Frame Rail braces, we just happen to utilize the same mounting points as our braces. Installation will require drilling through your floor similar to installing Frame Rail Braces.
If any part of your exhaust mid pipe hangs lower than the OEM Frame Rails, it would likely contact the Flat Underbody. Most aftermarket systems don’t have this issue, but we have seen some custom set ups sit a little too low for comfort.
Rear Section of the mid pipe should ideally sit higher than the lowest part of the OEM Ladder Brace. If the exhaust pipe sits a little low in this section you will be able to space out the flat floor to ensure the exhaust does not contact it.