The only difference in the 54104 and 54105 is the mounting hole is about 3/4" short on the 54104 making it slightly stiffer then the 54105. Like Emilio said this makes no difference when using heimed endlinks.

I've always wondered if either bar had enough meat in the opposite direction to just drill another hole and have both options.

 

Props for the details - thanks!

 

Heavy duty mounts for the sway bar not included?

 

We have never found a need for them.

 

Is there a noticeable or significant improvement from switching from the 95 stock rear sway bar (11mm) to the 14mm?

 

For autocross, the stock bar is fine. For backroad or track use, an 11mm doesn't work.

That said, if you really like the way the car works now with the stock bar, don't mess with it.

 

This subject is one that continually frustrates me due the misconceptions I read and hear around the community.

Close enough
The way most aftermarket sway bars are engineered for most cars is sort of random. In almost every case, a product engineer is charged with making sure the bigger bars fit. In almost no cases however, is an expert driver, with an expert at race setup involved in the development process whether it's a Mustang or Miata. In many cases, if it's a US based company, the bar stock is simply whatever inch size is cost effective. Thus you end up with a lot of 1" and 3/4" sway bars, whether that's the spring rate needed or not.

Who is doing the development?
A sway bar manufacturer might in some cases test the hardware on a Miata to make sure they work without interference/binding but are they optimized for the alignments, tires, wheel widths, spring rates we run? Is that test car running lap times as fast as a national championship level car and driver? Or is it simply an employee with a little motorsports experience on a nearly stock car? My question is, how does a non-expert driver and non-winning race engineer determine what handles well? The answer is, they can't. This is how we end up with oddball diameters that don't seem to match any known winning race set up.

I recall Racing Beat's testing done at SOW with their super soft lowering springs and I believe KYB AGX's, 200+ treadwear 205/50/15's on 15x6 wheels with nearly stock alignment. The front bars are all pretty close to perfect. The rear bar almost twice the rate required, oops.

Further, some cars only really need a bigger bar at one end only, but a sway bar company doesn't make as much profit selling one bar. So they take a guess and add a bar at the other end. Looking through the aftermarket catalogs for rear sway bars sizes on the 90-05 Miatas, the diameters are all over the map and nearly everyone of them too large.

Sway bars are part of a larger system
We settled on the combinations in our kit over several years of racing. While we were doing this, we were pioneering the application of 9" wheels for backroad and track Miatas. Mix in our race alignment refined over hundreds of ours on track. Xida's conceived, developed and put into production. Along the way we won more than a few races and set lap records at every track we visit. The point is there is nothing random about this particular combination.

For medium to lower grip tires and street uses, the .125 wall tubular bars. For 8-9" wheels with race tires, the .188" wall variants.

Until we find or create an even better solution, these bars represent the current gold standard.

 

This may be a dumb question, but is there a way to get just the 14mm rear bar from you?

I'm going to play around with rear-bar combos here soon. No bar, 12mm, and finally the 14mm. I'm not enjoying the under-steer on entry on back-roads with no rear :(. However I do like the stability on low speed transitions on an auto-x course.

 

Only direct from Mazda. We don't offer it separately.

 

Based on the RB chart, it looks like the NB 1.125 bar is slightly stiffer than the NA 1.125 bar.

 

54107 and 54103 are about the same stiffness. The 54105 is softer than both.

 

Don't you use the RB brace kit which achieves basically the same thing?

 

I think you might not understand what the different Racing Beat hardware components do.

The sway bar is a torsion spring, available in different spring rates.

The 3' long white sway bar brace that spans the sway bar brackets, is intended to reduce independent lateral deflection of those brackets. In our experience, we have never observed enough lateral deflection to be a problem so we do not even offer the brace bar. The sway bar brace has no effecy on sway bar spring rate.

The brace bar brace hardware is two small rectangular aluminum blocks that go inside the brackets to keep them from being squeezed flat under sway bar loads. We install the brace blocks on every car we build and they are included in the SBK.

A lot of folks get the brace bar and brace hardware confused.

 

Emilio, I am transitioning from auto-x to track days and haven't had problem with rear. What is it that makes track need the larger rear sway? I'm running 500/300 and was considering rb hollow front bar and stock rear since it has a pretty good FRC and figured since it rather good that I wouldn't need to upgrade.

 

Steady state mid to high speed vs low speed transients.

 

Thanks for clarification on that. Guess what my next order from you guys is. In auto-x I never needed it, so going to take a lot of relearning my car at higher speeds.

 

+1 to that sweet spot in car control where you can do things in a car that people get all excited about.

 

Just got done ordering the kit - guess I'm stuck with the .125" wall - didn't see the .188" variant available for my '91, unless you have something I didn't see that will work better. Still will be hell better than what I had before

 

I believe with adjustable endlinks you can put any bar to work with any chassis from 90-05.

 

You need the 54107. I'll switch it.