The great suspension bushing debate- rubber or poly...
 

So I've determined that my next project will be to replace all of the suspension "bushes", considering I have just over 150k on the car now. I have done my searching here, CR, and a few other places. I still cannot come to a conclusion on what I want. I plan on buying a set of control arms and working on the bushing swap as I have time, followed by having a friend help me do a "swap all the arms at once" project where I can take the car for an alignment right away. Ideally, I'd probably replace the eccentrics at the same time (I don't know why, I just keep reading that they should be replaced).

I'm torn between the all-rubber I.L. Motorsports kit from FM and any of the poly kits. So far I cannot find any real difference between poly kits, so I'm open to recommendations on that as well. Oh, I also plan on just doing the control arms and diff. bushing. Here is where MY thought processes have left me-

----Rubber----
Pros-
*No noise
*No need to re-grease/maintain

Cons-
*More expensive ( $379 from FM)
*More labor to replace (but I won't be pulling the arms off, then pressing out, then pressing in and putting back in car. I will be doing the bushing swap on a spare set of arms on my own time)
*more flex than poly?
*arms don't move as smooth as lube'd poly/more friction as arm moves??

----Poly----
Pros-
*Easy installation once rubbers are removed
*super slippery grease
*MUCH cheaper ($123 from FM)

Cons-
*need to drill and install zerk fittings
*need to stay on top of keeping greased
*too stiff?


So the big thing for me is the rubber's ability to be "install and forget". But, how much is this really "worth"? Is the $250 difference worth the ability to not need to maintain them? My gut says the rubber sounds like a better idea, but the idea that fresh grease on the poly keeping friction low is really attractive. Drilling and installing zerk fittings doesn't bother me, it's not really a factor for me. My problem for this is the mess/dirt that will inherently collect around the edges where the grease will clearly start to weep out; I'm slightly worried that this dirt could get in and cause wear. I've never ridden in a car with poly bushings and don't know what noise to expect. I do have a lovely and loud exhaust, but it doesn't bother me. I have a Beatrush PPF/diff brace that adds a fair amount of diff whine into the car, but I don't mind it. I also have a Carbing transmission brace that is a bit loud. But there are noises I DON'T like....like squeaks, creaks, pops, groans, thumps....or anything else that makes the car sound old and busted. Heck, I'm about to ditch the 949 endlinks in favor of some RB ones because the 949 ones click/pop over expansion joints.


So what are all of your thoughts? I know more of you folks are tuned to details like this.

Anyfucs, thanks for taking the time to read my crap.

Come to portland and borrow my car for a day. Poly control arm bushings, mazdacomp rubber diff bushings. Then try Stormin Norman's NA with aluminum diff bushings and delrin motor mounts.

Bushings of all types eventually are a wear item if you own the car long enough.

Personal opinion based on my experiences:

Street car = rubber
Track car = poly

Some may say poly is fine for street, but for me it was the straw that broke the camels back. Ride was a little too "communicative". Unless you love feeling every pebble in the road, keep the rubber.

I had poly on my 00' and after they "broke in" it wasn't bad at all. It was soo noisy at first, but they got quiet and the ride to me felt great. I was on stock seats though.

Sounds like you would be happiest with rubber bushings, with a second set of a-arms you can take your time to install the more difficult to install rubber bushings and they won't have a chance of sounding "old and busted" like poly could. The extra cost of rubber is offset in a way by the "set it and forget it" nature of those bushings.

I am leaning towards a hybrid solution with different materials in different positions, ILM rubber on lower inners, poly everywhere else and ISC racing offset delrin on the front upper inner pivot points.

My reasoning with using rubber on the lower inners has to do with how the rubber has some built-in give to it when the 2 lower arm pivot points get twisted out of pivot alignment. From my understanding poly/delrin bushings can bind slightly and make more noise if an unequal camber adjustment is made to the two pivot points on the same arm(i.e. caster on the front lower a-arms).

My car gets street driven, therefore I am leaning against going with ISC racing metal spherical bushings on the lower inners.

Not quite the same thing, but my buddy put poly bushings in his Mustang. Took it from a harsh ride to a jarring one. Made it damn near impossible to ride in - felt like the thing had steel wheels with wooden spokes.

It also squeaked, but knowing him he never lubed them.

Rubber bushings made it 150k, so why not give rubber another go?

Pros: No maintenance/No squeaking/OE feel

Cons: Cost.


Poly seems to be reversed. If you buy poly, hate it, and have to redo it, even if you value your time at 0, will cost more. Buy it once, do it right. Eccentric bolt threads can stretch over time, it has more to do with the environment they live in (road quality, frequency of alignments, and hard use). So, at $80 for a complete set from 949, they're cheap insurance from finding a bolt that is bent or refuses to tighten after you do all that work.

EDIT: If you're picky enough to remove the amazing 949 links, and replace them with RB bag-of-dicks, you'll likely not be interested in greasing bushings, and added harshness.

You'll have two sets of a-arms.

Do both, it's a $123 difference.

Sell the one you don't like. My guess is you'll put the poly's in and learn to love them. I think they're only as harsh as your suspension, so if you've got ricelands, you're going to have a bad time. But Xida's should absorb a lot of it. Dunno what you have.

Miata rubber bushings actually have very little rubber and flex on them, they have a metal bushing sandwiched between the a arms and the bolt bushing.
We made a set of Delrin bushings with offset holes for our STS car to tinker with suspension geometry a few years back and will not be going through that exercise again unless it is a track only car.

From what you've said it does sound like you'd be happier with rubber.

It does kind of suck that they are so expensive.

I've been having this same dilemma, my solution so far has been to not buy either...

Apparently the benefits of poly bushings are more internet myth, than subject of great debate. Tony at TCD Design Fab is THE MAN on building (and driving) race cars. He adamantly steered me away from poly. Apparently rubber's good enough for him on his race cars, but says Delrin is superior (but require a lot of work/machining to insure they dont bind).

Efini: Apparently a lot of road racers prefer OLD Miata bushings over the new ones (they're harder)

Poly.

On my Miata, I did the ES. The black ones are supposed to be graphite impregnated, so those are the ones I got. I put zerks in but have yet to have to use them. There has been no noise yet, I guess I used enough of the goo. They're a tight fit, I don't think I'd be concerned about dirt sneaking in, there's no room for it!

The ride is definitely more composed, it feels like a newer chassis. Unless you just have to stay OE, I say go for the poly. If you do rubber I don't think you'll feel much of a difference at all.

Where do you put the ky jelly?

Well, the 949 links have been on awhile and have play in them. I honestly have not put a lot of thought into endlinks yet...since they're so easy to do. I want to work on the harder stuff first. I'll dive into endlinks later though.
I think I've had my car aligned like 3 or 4 times in the 5 years I've owned it, so who knows about the eccentrics. I'll probably get them as a "in case" when swapping out the arms.

Good idea. I could always toss some poly bushes in the arms that come out and if I'm happy with the rubber, I could probably sell the set with bushes for a fair amount of money to recover some of the costs (I'm sure someone would be willing to pay to have the PITA work out of the way).

I'm still running Ohlins DFV coilovers.

Interesting. I've been reading the SM guys like old rubbers....I'll take time to get mine out carefully and see if I can make a few bucks lol.

Did not know the black ones were graphite infused, I wonder how much of a difference it makes. The IL's are supposed to be "30-40% stiffer"...I'd hope I could feel it lol. When you say "tight fit", do you mean you needed to press the halves in or did they go in by hand?

I'd be inclined to say Hustler probably keeps it in his mouth so he can lube up the next shaft that he'll be bending over for. :giggle:

If you do decide on rubber, then I recommend you inspect what you have first. If they're not bad, then they're not bad. They can easily last 150K+ in areas where they are not exposed to harsh chemical/road salt/etc. I've got 200K on mine, and everyone that rides in the car marvels at how smooth and tight the ride is. It's a big enough project that it would be a shame to replace perfectly good parts. The time and money might be better spent elsewhere.

Yeah, although I guess my memory is flawed because here it says only the sway and front uppers are:
Energy Suspension Bushings Miata

Also 949 doesn't offer the red, which is fine because we all know that they wouldn't be pretty red for very long under the car anyway.

The halves went in by hand. It's a bit of a squeeze and you definitely need the grease. I used a hydraulic press to get the rubber bushings out (I tried the idea from the redneck press thread and the allthread broke on the first bushing, probably too thin) and so there wasn't any leftover grit like there might have been if I burned them out.

I could tell a difference but it's more minimal than you might think. I definitely don't think it affected the ride for the worse. If anything the ride actually improved. But when you're talking about a car with 700# springs, ride comfort is relative I guess.

I love the poly, but YMMV. I would hope everyone else here with an opinion one way or the other is posting from personal experience and with info relevant to Miatae.

I echo the

If comfort is goal = rubber

Otherwise polly. You definitly feel more connected to the pavement from a "feel" standpoint. Sometimes I think I could tell if I ran over a quarter.

id probably do rubber if I did it again.

I think poly bushings are to ride quality like CD players were to audio quality when they were first introduced. People got one, played a CD, and thought it sucked - because the signal quality of the CD player exposed weaknesses in their audio system that were previously masked.

Same with poly bushings and ride quality. The flex of the rubber bushings will serve to cover up and mask deficiencies in your dampers. Since you have good dampers already, I say go poly. You will not notice any difference in NVH since you have a loud exhaust already. I have not noticed any NVH differences with the poly bushings on my car. (Edit: with both my louder Enthuza muffler and the stock muffler, no NVH difference I can detect). I cannot compare damper settings directly to before and after the bushing swap, since I swapped dampers at the same time (from Tein Flex to Xida CS). But the control arms are definitely more free in their range of motion with the poly bushings, which is a good thing.

I have poly bushings (the purple one's from FM, can't remember the name but there was some wacky kangaroo on the package) everywhere except the upper front control arms, where I used offset delrin bushings to bring the camber range back to the middle of the eccentrics, and I'm happy with them. The car handles great, and doesn't make any really objectionable noises. As I understand it, one advantage to poly is that they're free throughout their range of motion, where rubber ones progressively add resistance and effectively make the spring rate increase as they "wrap up" as the control arm moves. (And obviously, they can't deflect laterally under load, preventing minor changes in alignment as you go over bumps.)

If I was a Wine And Cheese-er guy with a full compliment of IL Motorsports interior shiny stuff I'd probably not go poly, but for a car that gets driven hard (and an owner willing to grease them every now and again) the poly bushings are the way to go. My car feels MUCH more precise in hard cornering.

Funny you mention I.L. Motorsport.... I am just at the same point as the O.P. with my project Trisha MXMillan and have to decide between Poly or rubber.

I.L. Motorsport actually offers a set of imporved (stiffer) rubber bushings:

Gummilagersatz kmpl. vorne + hinten

Here in Germany there isn't much of a price difference between the poly and rubber bushing sets...

Maybe for a daily AND track car the implorved poly bushings could be something like best of both worlds? (This is a question - I have no idea...)
They are developed for the MAX5 racing series...