Back about 6-7 years ago, somebody thought up a neat and tidy way to try and stiffen the chassis of the Miata a bit, a pair of hard plastic door bushings. If you don’t know what I talking about, here is a little primer via the Flying Miata website:
The Miata doors are held closed by the latch, but they’re locked into place with a bracket that slides over a rubber bushing. That makes it easy to align everything, but it means the connection isn’t as strong as it could be. In a convertible, the doors provide a surprising amount of structural rigidity if they’re properly anchored.
Ours replace the soft rubber door bushings with a stiff, carbon fiber reinforced nylon replacement. The door is solidly locked into place, allowing it to reinforce the chassis. The effect is of a stiffer car with fewer squeaks. We have measured a 3% improvement in torsional rigidity on a 1990.
Folks in the Miata community were quick to adopt this little gizmo. Opinions on their worth though ranged from ‘snake oil’ to ‘really tightens things up’. Around this time the Emperor had about a 150,000 miles on it I thought, “I could use a little chassis stiffening, what the heck, for $35 its worth a shot.”
When they arrived I went right out into the garage to install the Garage Star black Delrin bits. It was pretty simple, take out the OEM rubber pieces and install the firmer plastic pieces semi-tight, close the doors so they get centered properly and tighten fully. The passenger side door closed as before, but the drivers door had to be almost slammed hard to get it closed. I took the car out for a quick spin to see if I could feel a difference. As I backed out of the driveway and took the little dip at the road, I could swear the car felt tighter, so I took a drive to the closest set of railroad tracks. The there results were the same.
Now I can’t swear there was actual improvement, might just have been the placebo effect, but I wanted to keep them on the car none the less. I looked for advice on the M.net forum and tried a couple things I found there to get a slam-free door closing. Swap the sides of the bushings, sand the bushing a little and bend the metal door cup out some, but nothing helped. I left them on the car and settled into having to semi-slam the door shut. About a week and a half later, I took them off and put the stock rubber pieces back in. The Delrin bushings went on the shelf in the garage.
Fast forward a year and the Emperor gets replaced by the CTBNL. When I bought the car it came with a box of random stuff, the stock horn (it had air horns installed) a selection of plastic Miata related fasteners and a set of Delrin door bushings! This peaked my interest in the bushings again. The “new” Miata, even though a model year older than the car it replaced, had only 43,000 miles on it so maybe the effect wouldn’t be as great. And why did the previous owner have some in a plain marked up plastic baggie? So I tried out both my old bushings and these new ones. This time it was the passenger side that now needed a semi-slam to close. I fiddled around just a little to try and cure the slam requirement and gave up. Both of them went back in their respective bags and then into the “box-o-parts” on the garage shelf.
Well, here we are a couple of years later and that box with those two sets of Delrin bushings still sits on a shelf, but in a different garage. So you would you think that the last thing I would ever need to buy would be a set of Delrin door bushings and you’d be right.
I bought some door bushings made of Polyurethane.
Polyurethane is a slightly softer material compared to Delrin, but it is still a lot stiffer than the OEM rubber bushing. Sooo…there might be a bit more chassis rigidity achieved with them, but that is just OK, because these are more of a fashion accessory than a performance upgrade. These poly bushings are of course offered in black, but the big draw is that they come in 7 colors, plus clear, to dress up your door opening. I went with Translucent Blue which sort of mirrors the blue stripes on the car.
These bushings worked great first time. To make it a little easier to open and close the doors I put a little Armor-All on them and now they need just a scooch more effort to open and close than before, but no semi-slam required. Get your own colored Miata door bushings at Spiked Performance.