I can make a few guesses:

1. Because usefulness of a diffuser without proper suspension height and ground effects is marginal at best, negligible at worst, and a weight increase regardless.
2. Because a splitter and a wing accomplish a pretty ideal distribution of downforce at a much lower cost.
3. Because the Miata already handles like a bat.
4. Because Miata drivers are cheapskates and there is not a market large enough to bring them to the non-racing crowd.
5. Because the Miata racing crowd drives spec.

We had no idea Velox was working on ND bits until a few days ago. Read the white paper-ish doc they emailed me and was convinced. If all it does it reduce lift by a measurable amount, I'm in. That they did full pro level aero analysis appeals to my data oriented mindset.


ND is still a great car. I would like to see less toe steer in the rear though. That would allow us to run less aggressive toe settings, less low speed damping (better ride quality) and lower spring rate (lower bounce freq for better ride). The bump steer curve in the ND is super focused to work at stock ride height with low grip tires, stock damping and spring rates. Brings to mind the 86 twins, in which the engineers allowed for lowering a bit while retaining desireable bump steer and roll centers. They knew owners would lower them and built that into the suspension. Mazda didn't.

As it is, I can't make the ND ride as well as an NA/NB while retaining good limit behavior with high grip tires. We fussed over the valving, spring and roll rates on the ND Xidas for quite a while and had to "settle" on making the limit behavior correct but never quite reaching my ride quality targets. It's good, but not "great" like the NA/NB BGK.

:likecat: Thanks for the explanation, Emilio.

Thank you for the explanation! I always wondered why you warned against high spring rates on the ND giving bad ride quality, but I had never heard a bad word about 700/400 on the NA/NB's with your XIDA's.

The motion ratios on the ND are also different than the NA/NB, which dictates lower spring rates for similar wheel rates and bounce frequencies. Key difference is F&R NA/NB being very similar averages although the rate change in rear is greater. So shock valving is similar front to rear. ND has about ~40% lower motion ratio in the rear compared to front. So valving is radically different front to rear in the ND. Toss out the pesky rear toe steer of the ND and I'd run much softer spring and damping rates. But since the toe steer can't be "fixed", we band-aid that design characteristic with damping and spring rate.

I think you've mentioned this rear toe steer thing a couple of times now.
I know very little about multi-link rear suspension setups other than mercedes had to use state of the are computers back in the 80's to make it work on the w201.

Can you fix it? Arms are cheap to manufacture... It's like Mazda is baiting you.

Good arms are not cheap. I think it would require a new upright.. $$$
In any case, we're happy with the handling now. Just hoped for better ride quality on the stiff springs. Not a huge deal. I wouldn't worry about it. Of course, folks will read my post, take it out of context and cry that the sky is falling.

The toe steer is a part of the "multi-link" rear suspension geometry, right?

--Ian

So, if you don't mind, I would like to throw out some of my thoughts on the suspension issue.

Is the toe steer immediately made worse by any lowering at all? You can't even drop it an inch before it goes whacky?
If so, how about running 15's and using their shorter profile to drop the car and not lower the ride height much, if at all? For instance, you run a 245/40/17 currently for track stuff. Running a 245/40/15 would make the car 2 inches lower and then the toe steer could be left in its happy zone. If this thinking deeply flawed? If the toe steer could be negated by not dropping the suspension height, would your ND Xidas be able to be revalved to take advantage of that and get the ride quality back?

I am sure the ride isn't that bad, but by how far did you miss your ride goals with the ND Xidas?

going to a 15 from a 17 makes the car, at most, 1" lower assuming the same tire profile (which you are).

245/40/17 is 24.7" diameter and 245/40/15 is 22.7" diameter. Two inches less on diameter only drops the car 1 inch? Well, I am retarded then.

Yes, because the radius is what would effect the ride height change, and a 2" larger diameter wheel is only 1" larger radius.

What we have here is a fundamental misunderstanding of the difference between radius and diameter.

Indeed we do.

Well, now we have established that I can't do basic math and shouldn't be allowed to even drive a car. I still question if the 1 inch less total ride height with the 15's compared to the 17's fixes the toe steer problems because the suspension is 1 inch higher.

Maybe

But it'll still look like this:

https://cimg8.ibsrv.net/gimg/www.mia...812d2e9f1d.jpg

and this

https://cimg0.ibsrv.net/gimg/www.mia...578033fe3f.jpg

This looks slightly less horrid due to the style of the Advanti wheels exaggerating their size... but only slightly less horrid.

https://cimg3.ibsrv.net/gimg/www.mia...c173c9ff7f.jpg

I have zero problems with that. I have several sets of 15's that would work well. Plus, I am mostly referring to track use. Emilio is saying at-the-limit handling is the where the toe steer issue arises, so running a funny looking size on the track to (possibly) fix handling issues doesn't bother me at all.

I don't think it's math that should disqualify you from being able to drive

I think it's the fact that you're blind

:giggle:

I chuckled. Props.

https://cimg2.ibsrv.net/gimg/www.mia...2a7a02d439.png