So I took my 2021 Miata RF out for the first time this season a couple days ago. For reference, it's a GT, so it's got the factory Bilstein suspension.
Right now it's bone stock, and I'm going back and forth between the idea of keeping it that way or adding a set of sway bars. It does roll a lot, no question, but it's also really entertaining to drive as it is, and it probably helps to keep speeds down to reasonable levels. When I drive my 128i, which on paper has very similar performance to the Miata but has upgraded springs, dampers, and M3/1M control arms, I find myself driving significantly faster if I just settle into what feels like a natural speed. Not necessarily a good thing on public roads, and that's the only place I anticipate the Miata being driven. But I do find the body roll distracting.
The other consideration, probably secondary, is what it would uprated bars might do to behavior on the highway. While it's not a long distance cruiser by design, I am strongly considering using it for some serious road trips in the future, and I don't want to exacerbate any already less-than-ideal ride characteristics. In this vein, I'm also wondering about things like door bushings to improve chassis rigidity.
I know I could dial in exactly what I want with coilovers and such, but I'm not going down that path here. The car's going to remain mostly stock, with whatever little tweaks I can make to get it as close to ideal as possible. Happy to hear thoughts on this, though I know my limitations and vague objectives leave a lot open to interpretation.
Has it been aligned yet? That helps a lot with things like steering feel and overall precision.
A well-chosen set of sways won't affect the highway use, just make it a little sharper in the corners and cut down (not eliminate) roll. The fronts are a PITA to install but it's worthwhile. Your stock springs and shocks are one of the best stock suspensions ever shipped on a Miata (they get Bilstein setups wrong most of the time) so it's a good all-around choice along with good sways.
In reply to Keith Tanner :
I have the alignment specs you provided, but I haven't lined up the service yet - probably in the next month or so.
On the sways, and I realize this may be difficult to quantify (unless you have actual testing results, which you probably do), how much of a reduction in roll stiffness could one expect from the FM sways set to the softest position?
I have numbers for the FM bars, I'm looking to see if I can find the stock ones. I've got weight and diameter and wall thickness for stock, but I don't know if we ever made note of actual rate. You have to watch out for this unless you spend a lot of time with the numbers, the increase in bar stiffness (percentage-wise) has to be fairly significant before you start to notice. Heck, there's nearly a 100% increase from full soft to full stiff on the FM bars.
Upgraded sways are one of those few modifications that has little or no downside, especially with the light bars that Mazda uses.
Wow, 100% across the range of adjustment is a lot higher than I expected. I suppose a lot of this is somewhat subjective too, but numbers certainly help to clarify things.
What's your feeling about the door bushings and other chassis stiffeners for the ND in pure road use? Useful or overkill?
That's why we don't usually quote the actual numbers, people tend to misinterpret them. Remember that you don't get 100% of your roll stiffness from the bars, they're only a partial contributor so doubling the stiffness of the bars is not double the roll stiffness. Unfortunately, I don't have the specs for the factory bars.
Door bushings are funny. They're by far our most reviewed product and the large majority are positive. For some people, there's no discernible difference. We did measure a difference in torsional rigidity on our test rig, but my general view on them is that it's low expense and low effort with zero downside. If it works, great. If not, well, it's not a big investment. At the very least, it adds a nice solid thunk to your doors when closing. I have them on a number of my own cars.
The ND is pretty stiff. I don't think we've come across a brace that we've tested that's an improvement. It's not where I'd focus my attention.
Yes, I understand the sways don't operate in isolation. It still seems like a more substantial increase than I expected.
I think I may have to just get some bars and try them out to see if I like it, or if it changes the feel too much. Thanks for your input. Expect an order fairly soon.
I'd strongly recommend watching our install video before installation. That front bar is a brute.
Charming. I'll give it a look. Thanks.
Finally got to install the FM sway bars on my car. I found words other than "brute" for the front bar, words not suitable for polite company - it is really wedged in there. I seriously considered taking an angle grinder to it and chopping it in half, but I resisted (barely). All told, the whole job front and rear took about three hours. The test drive shows marked improvement; on the middle setting the car feels a lot closer to what seems appropriate for the chassis. I may still want to move both bars to the stiffest setting, but I'm going to drive it a bit more before I make that decision. Overall, an entire worthwhile improvement, one which could only be made better by having someone else do that miserable front bar.
