NA Miata Sway Bar Upgrade Guide

Whether you’ve got a 1.6L or 1.8L NA Miata, the best mods are suspension and handling mods. Power is expensive to make which is why we recommend putting your money into suspension and handling with things like coilovers and sway bars.

Sway bars, also known as anit-roll bars, help prevent body roll and lean during cornering. Less roll means tighter cornering and better handling through the twisties. Outside of a set of stiffer coilovers, sway bars are one of the best handling mods for the NA Miata. This guide is going to cover how sway bars work, the benefits of upgraded NA Miata sway bars, and our recommendation for the best sway bars available for the Miata.

How Sway Bars Work

Sway bars essentially connect the left and right side of the front and rear suspension. When you take a corner, the body weight of the car shifts to the right. This puts more force on the right tires and essentially lifts the left tires off the ground. The weight of the car shifting to the right side is what we call “body roll”. Body roll essentially creates a twisting force, also known as torsion.

Sway bars work to counter the shift in weight to one side and create even weight distribution. When the weight begins to shift, the anti-roll bar essentially twists which transfers weight back to the other side of the car, minimizing body roll.

For the NA Miata aftermarket sway bars come in different thicknesses and materials, each of which has an impact on the stiffness of the suspension.

Miata Sway Bar Upgrade Basics

There are a few considerations with aftermarket sway bars for the NA Miata. The most important things to discuss are thickness, solid vs. hollow, and adjustability. Ultimately, the best setup for you likely depends on your goals and whether your Miata is being used for track days, street driving, autocross, etc. Additionally, we will touch briefly on end links.

Sway Bar Thickness

The front sway bar on NA Miata’s is 19mm for standard models, and 20mm for R-package Miata’s. The rear is 12mm for ’90-’93 NA6 models and 11mm for ’94-’97 NA8 models, with the exception of cars with the Torsen LSD which got 12mm. The factory roll bars are rather small in size to create a balance between comfort and handling.

Aftermarket sway bars for the Miata range from about 22mm-25mm in the front, and 14mm-16mm in the rear. Tubular, or hollow, sway bars then to slightly bigger diameters due to the thickness of the piping wall. Ultimately, the thicker the bar the stronger/stiffer it is and therefore the greater effect on body roll.

A few general rules here on the Miata:

Thicker front sway bar = more understeer.

Thicker rear sway bar = more oversteer.

Most autocross guys stick with the stock rear bar since an upgraded bar causes too much oversteer. If you do autocross, here is a really good guide on Miata autocross sway bar sizing. Additionally, a lot of people say 16mm is too big for track day events as it causes the rear end to swing out a bit too much. Ultimately, it’s setup-dependent but 14mm and 15mm seem to be more track-oriented and the stock bar is autocross oriented.

I put the 16mm rear bar on my NA6, so we’ll see how that works on the track. But realistically, if you aren’t an experienced and serious track guy, then I really don’t think you’ll notice the extra 1 or 2mm.

Solid vs. Tubular Sway Bars

There are generally two options for the material of the sway bar. You can get a fully solid sway bar or a tubular one that has a hollow inside. The two biggest differences between the two are strength and stiffness. Solid sway bars are going to add weight over the stock sway bars, which are also solid. Per the Racing Beat solid bars, the rear is about 1.3 lbs heavier and the front is about 4 lbs heavier than stock. I can’t find weight data for other brands, but I imagine it is about the same.

Tubular bars on the other hand are 1) stiffer than solid bars, and 2) significantly lighter. Per Racing Beat, the tubular front bars are approximately 1.3x as strong as the solid bars. Additionally, they weight about 5.5 lbs, compared to 6 lbs for stock, and 10 lbs for solid.

Tubular bars are only available for the front sway bar. A tubular rear bar would likely be too strong and stiff causing too much oversteer. There are a lot of track Miata drivers that say go as stiff as you can go on the front, making tubular a popular option.

Adjustability

Most, but not all, NA Miata sway bars have different levels of adjustability. Front bars usually have 3 levels of adjustability and the rears commonly have 2. At a high level, the different adjustment settings affect the stiffness of each bar. For daily driving keeping the front at the middle setting and the rear at the lower setting is most common. Tubular bars typically don’t have adjustability.

We recommend adjustable sway bars. Having a few different settings you can tweak is ideal for dialing in your suspension setup.

Endlinks

Endlinks connect the sway bars to the suspension. The stock endlinks are pretty skinny and not super strong – especially if they are 30 years old. I just upgraded the sway bars on my NA Miata the other week and the endlinks were the 30-year-old stock ones and were completely toast.

Unfortunately, end links add about $150 of cost to upgrading the sway bars but they are a must. The stock endlinks, unless they are brand new, are going to bust pretty quickly once you add the extra strength and stiffness from the upgraded bars.

Best NA Miata Sway Bars

Fitment does differ for NA6 and NA8 models, so keep that in mind. Sizing does differ for some of the brands as well based on models. Again, I will note that the best option is really setup dependent and personal preference. Some drivers are okay with more oversteer on the track, some aren’t.

Your coilover or spring/strut combo will also have an impact on this. If you are building a competitive track or auto-x Miata then your best bet is going to be to consult with the hardcore event drivers on best setups. I do own a ’92 Miata NA6 and run the FM bars with MeisterR Club Spec coilovers, but I don’t track or auto-x enough to give you a serious opinion.

• Eibach
• Flyin’ Miata
• Racing Beat
• 5x Racing 14mm Rear

Our Number 1 Pick – NA Miata Eibach Sway Bars

Eibach sway bars top my list primarily for one reason: these are the Spec Miata sway bars. Both NA6 and NA8 versions have a 24mm front bars and 15mm rear bar. It is a solid bar so it isn’t going to be as stiff as a tubular option, but the rear comes in at a nice 15mm which should still be good for track use. Spec Miata’s run 700/325 on spring rates which is rather stiff, so these bars should be complimentary to a more street oriented suspension setup as well as track cars.

Eibach’s anti-roll bars are adjustable with 3-levels in the front and 2-levels in the rear. I understand Spec suspension isn’t the most fine-tuned setup for track cars that don’t have specific requirements, but these are the spec bars for a reason and are very similar in size and pricing as our other options.

Price: ~$375 for the sway bars, ~$150-$200 for endlinks

NA Miata Sway Bar Summary

Sway bars are my second favorite NA Miata mod, just behind coilovers. Sway bars reduce body roll which in turn improves handling and cornering. There are a number of considerations for sway bars when it comes to thickness and design. A lot of people believe in going as thick as you can go in the front. The rear is a bit more use-dependent, with 16mm options being a bit too stiff for autocross and track events. Tubular front bars are great for maximum stiffnes.

Overall, the best sway bar really depends on your goals and your driving style. I run the FM NA6 bars with some really stiff coilovers and my NA corners like a boss on the streets. However, I am not a track or autocross expert so I’m not quite as particular. Overall, on a stock Miata sway bars will be a noticeable upgrade to handling and cornering. For the track aficionados, consult your local experts.

What’s your NA Miata sway bar setup?