1994 Mazda MX-5 Miata: Overhauled Suspension
May 12, 2010
Ditching Project Miata's stock suspension wasn't a tough decision. The tepid roll stiffness and tired dampers meant that when driven over bumps of any significance, the car was constantly bouncing off the bump stops. And although you could sense the underlying Miata goodess, it was covered in a thick layer of suck.
The colorful bits you see above -- Fat Cat Motorsports coilovers, a Racing Beat tubular stabilizer bar and 949 Racing endlinks -- represent a first step in eradicating the suck.
Hit the jump to see what they're all about.
Now, it isn't unusual for stock cars to employ the bump stops as supplement spring rate to the coil springs, but we're talking 1994. Bump stop technology had some way to go. An NA Miata's bump stops were made of hard rubber. Not quite hockey puck material, but getting there.
Together with the scarce bump travel of a stock Miata's suspension, the effective spring rate goes from very soft to holy crap in a hurry. This nonlinearity in spring rate makes for a car that is bump-sensitive, a situation that has obvious ride and handling implications particularly when the dampers are worn.
Fat Cat Motorsports Coilovers
Fat Cat Motorsports (FCM) coilovers address the Miata's inherent issue of limited travel from a number of angles.
First, the upper shock mounts use a later Miata (NB) configuration, which locates the bump stop higher, allowing for more bump travel.
These bump stops are also shorter than stock and made of a material that provides a more progressive increase in spring rate than the hard stock units.
And of course, the higher coil spring rates do a better job of preventing the suspension from bottoming in the first place. Our FCM coilovers have 425 lb/in front and 300 lb/in rear spring rates, which get us in our 2.0 Hz ride frequency ballpark.
With the increase in bump travel allowed by the FCM coilovers, we've lowered the car by about an inch to bring the center of gravity down a bit. Lowering is a tricky subject -- lower a Miata that still has the stock upper shock mounts & bump stops and you'll pound your kidneys out. Plus, go too low and bump steer can become an issue, never mind scraping everywhere.
With these coilovers, an inch is groovy. I can deal with that. It'll look better too, so Oldham will be happy.
Stock dampers are a twin-tube design, while the FCM shocks are custom-valved Bilstein monotubes. Monotubes have a larger piston area, which allows them to generate meaningful damping force at very small shock movements. In other words, the shocks can actually damp those movements, improving control.
Monotubes also dissipate heat better, which reduces damper fade that can occur when driving over rough surfaces. Probably not an issue on a smooth track, but nice to have on, say, the road to Mount Gleason, a rough, unmaintained stretch of tarmac that's one of our faves.
Unsatisfied with the valving on the stock Bilsteins that came on certain NA Miatas, revalving has allowed FCM to tailor the damper force as they see fit. These coilovers are FCM's entry-level offering and so the dampers have fixed valving, i.e. compression and rebound are not adjustable.
In case you're wondering what the heck this little dongas on the shock body is all about, it's a shrader valve that FCM uses to pressurize the dampers after they revalve them.
Basically, the sole adjustment on our FCM coilovers is via the threaded lower perches, which let you corner-balance the car and adjust the ride height. FCM's hex key adjuster is a bit fiddly but workable.
Racing Beat Tubular Stabilizer Bar
Trimming out the roll couple is a tubular front stabilizer bar by Racing Beat. It's big and red, about 3x stiffer than stock yet weighs about a half-pound less than the stock unit. Hollowness has its advantages.
The bar includes urethane bushings that are less squishy than the stock ones, which help the bar transfer load more effectively.
We currently have the stock rear bar (aka paper clip) on the car, as the roll couple in this configuration is pretty close to the stock balance.
949Racing Adjustable End Links
Speaking of stock bushings, the 949Racing end links replace the stock fixed-length jobs. That's cool since the bushings were being extruded out of our stock end links.
The metal spherical bearing eliminates a source of squish, which promises to make the front suspension react more precisely to steering inputs.
In addition, these end links allow you to remove preload from the stabilizer bar. Preload can result in uneven roll stiffness left to right and/or increase the susceptibility to brake lockup on the more loaded side.
Really, only one side needs to be adjustable to accomplish the preload removal, but there's no sense keeping a squishy stock end link on the other side. Especially since these are sold in pairs.
Cool details -- each rod end has opposite threading so you can just loosen the jam nuts and turn the center turnbuckle to adjust the length -- no need to disconnect the bearing ends. The conical spacers allow for maximum articulation without binding. And note the dust seals between the bearing and the conical spacers. These will help the bearings live a longer life.
Lots of impressions and track testing in the weeks and months to come. This will be fun.
Jason Kavanagh, Engineering Editor
Fixed-adjustment coilovers, MSRP $1,698
Tubular stabilizer bar #54105, MSRP $150
Adjustable end links, MSRP $89.95/pr