Miata Tire Wear (2022)

Alignment Specs

In an effort to try to understand why I had such unequal left/right tire wear on the rears, I pulled the car into the garage to check out the alignment. I setup the string alignment exactly how I had it when I aligned the car early last year. Here is a table showing the alingment specs.

I’m not sure why these numbers are so far off from what I had dialed in last year. I decided to correct the toe out on the driver front, and call it a day. Here’s a table showing where things landed after the toe adjustment.

Corner Weights

I also took a look at the car’s cross weights. The weights only make the tire wear even more puzzling. I was expecting to see the passenger rear tire with the most weight, but it was actually the lightest! Another puzzling thing, is that the car seems to have gained 100lbs since the last time I scaled it. I don’t know how that’s possible… I even made sure to scale the car on about the same fuel level (half tank).

Swaybar Settings

A few days after checking the alignment and corner weights, it occured to me that maybe this is related to my swaybar. I run a Flyin Miata swaybar in the front with no swaybar in the rear. Like most aftermarket swaybars, the FM swaybars have adjustable endlink holes, allowing you to tune stiffness. For the past 2+ years, I’ve been running with the passenger front endlink in the inner hole (stiff), and the driver front on the outer hole (soft). I hear people say running an assymetric setup like this is perfectly fine, assuming you can adjust the endlink length to prevent preloading the swaybar. I’m starting to question if that’s true…

After some thought, research, and experimentation, I think I’ve convinced myself that running assymetric swaybar settings is bad! Unless, you’re a circle track racer making left or right turns all the time, then you probably always want your swaybar setting symetrical. Here’s a forum thread that discusses this quite a bit. There’s a lot of back and forth on that thread, but pay attention to ‘winders’ posts; he really seems to know what he’s talking about.

Knowing that about swaybar settings, I decided to put my front bar to full stiff on both sides. My next autocross isn’t until January, so I’ll have to wait till then to see how these changes affect the car’s handling. I might end up losing the bar if it tends to understeer more. As for tire wear, I guess I’ll have to wait a little while longer before I notice anything significant.

Extra Info

FWIW, I recorded this video talking about the tire wear and what I was thinking at the time. Note that the video was recorded before I did all of this alignment, and corner weight checking.