The great suspension bushing debate- rubber or poly... - Page 2 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 04-29-2013, 09:54 AM   #21
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Poly bushings have the advantage that they are not glued to the center cylinder that the subframe/camber bolt clamps to. In theory they should offer a non-binding suspension movement like delrin, better durability than rubber, with less road feedback than delrin.

The rubber may not have as much flex as people think, but it does have enough flex to compensate for the alignment geometry changes that delrin and poly cannot tolerate and therefore bind. I've installed and raced on several delrin setups and never had any binding issues BUT all the setups were road race- no radical toe settings, so front/rear camber bolts were rolled very similar. All the delrin installs did require tweaking with a reamer and sander. I have done the same with poly bushings in shock ends and sway bars, but not control arms.

I raced showroom stock for years and the OE rubber bushings would eventually start tearing at the lower front control arms. You could tell when it started as the dynamic toe increase under braking would start to require more and more correction under braking. I hope to find that the poly will avoid this, and provide more accurate movement without any binding.

I don't see any real advantage to poly if you're not going to compete.
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Old 04-29-2013, 10:38 AM   #22
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Originally Posted by Doppelgänger View Post

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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.
Keep in mind that Spec Miata guys *can't* (legally) use anything other than OEM bushings, hence their preference for the oldest, hardest OEM bushings they can find, specifically because they're less likely to compress and deflect under load, which results in alignment changes under load.

I've been involved in building a few full-on tube frame race cars, and on those cars all of the suspension pivot points are heim joints; not a bushing to be found on the entire car. Clearly, from a NVH (noise, vibration and harshness) standpoint such a setup would be nightmarish on the street, but they maintain absolutely precise alignment regardless of load.

Go poly. Make sure you drill them and install grease fittings, and you'll be happy.
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Old 04-29-2013, 10:52 AM   #23
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The tough thing with poly, especially on these cars is that the zerk fitting needs to apply grease to the area in between the poly and the inner race, thats where they rotate around. So you need to drill all the way through the poly and run long thread zerks (holds the hole in the poly aligned with the zerk). The grease does nothing for your in between the poly and the arm because it should not be rotating there.

I'm kind of thinking the choices are rubber or sphericals. Poly has too many downsides (binding, needing to be lubed, not as stiff as delrin) and so does delrin (harshness, hard to get caster/toe [supposedly], wear [supposedly]). Sphericals should have ~same NHV as delrin but with no binding, and if they're sized and spec'ed correctly they should last a very long time.

I dont completely believe the delrin binding with caster or toe adjustments that I've heard, on the fase car we made oilite (oil impregnated brass) with a 0.05 thick delrin bushings setup for the front arms and there's a considerable amount of caster you can give the car with the uca eccentrics with no binding. Of course it has a separate caster adjuster from camber, but we tried it to test (and its really hard to move both camber adjusters on 1 arm perfectly together).
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Old 04-29-2013, 01:58 PM   #24
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For a track specific Miata I would use spherical bearings on the front lower arms. I like rubber out back for some deflection under acceleration. I would also leave front uppers alone with rubber.
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Old 04-29-2013, 07:10 PM   #25
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I don't think the rubber bushings in a Miata suspension provide much compliance. I noticed very little change in harshness when I installed poly. But I did notice that the suspension seemed to move freely in a way that it didn't with rubber, and that is the real advantage that poly has over rubber.

I've thought about a hybrid solution: rubber with a lubricated bushing. Not sure what the advantage woud be over poly though, as it would require maintanance which is the biggest advantage of traditional rubber bushings.
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Old 04-29-2013, 10:48 PM   #26
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Quote:
Originally Posted by Doppelgänger View Post
Heck, I'm about to ditch the 949 endlinks in favor of some RB ones because the 949 ones click/pop over expansion joints
Miata End Link parts
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Old 04-30-2013, 10:02 AM   #27
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Thank you Emilio. Don't take my post as knocking your parts in any way at all, I love them. I also understand that helm-joint parts will wear faster than a bushing. I've had them in for a few years (had Whitelines in previously) and understand that being exposted to temp changes, water and dirt will wear them out. I honestly didn't know you offered replacement parts though, good to know. I did get under the car the other day and pulled them off and lubed them up...they were very dry. Now that that is done, they seem much better....though looking at your replacement parts list I see the pictures show a seal as well as a part listing for it...mine never came with such parts and would make sense as to why they were dry/making noise.

After cleaning them up, I've decided to keep them

So what is your input on rubber vs poly for a mostly street driven car (but gets driven hard)?

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Originally Posted by m2cupcar View Post
Poly bushings have the advantage that they are not glued to the center cylinder that the subframe/camber bolt clamps to. In theory they should offer a non-binding suspension movement like delrin, better durability than rubber, with less road feedback than delrin.

The rubber may not have as much flex as people think, but it does have enough flex to compensate for the alignment geometry changes that delrin and poly cannot tolerate and therefore bind. I've installed and raced on several delrin setups and never had any binding issues BUT all the setups were road race- no radical toe settings, so front/rear camber bolts were rolled very similar. All the delrin installs did require tweaking with a reamer and sander. I have done the same with poly bushings in shock ends and sway bars, but not control arms.

I raced showroom stock for years and the OE rubber bushings would eventually start tearing at the lower front control arms. You could tell when it started as the dynamic toe increase under braking would start to require more and more correction under braking. I hope to find that the poly will avoid this, and provide more accurate movement without any binding.

I don't see any real advantage to poly if you're not going to compete.
Can you explain a bit more about the movement/geometry and binding? I'm trying to make sens of that but can't quite figure out how the difference in flex between rubber and poly have different outcomes on suspension geometry/alignment. Obviously I can understand that the poly will not allow the arms to move around as much (bushing compression when loaded/unloaded), but as for equating that to "binding" is what I cannot comprehend. I understand "binding" as an interference with the range of motion and cannot see how a stiffer bushing would have an effect on the range of motion that would cause it to bind up. Hell, come to think of it, I need to look more into this on my won as well (not just be told answers on here).

So I'm still not able to make a clear decision between the two. Longevity aside (because fittings + regular lubrication eliminates this problem), the idea of a more compliant/lower friction between the components sounds like a no-brainer and would allow the suspension to do it's job without putting any effort into its job, but with that said, if the rubber is less compliant, I can see the added benefits of a "bushing spring rate" added to the overall operation of the suspension. It seems from you guys that there really is no "bad" noise from the poly like I was thinking there would be, so that's good. I was more afraid of the poly being very prone to squeaks/groans and perhaps even a clunking/thud noise. I don't mind a lot of feedback because the coils/dampening can handle it. But lately I've noticed more shudder over some bumps and stuff and want to eliminate that.

Last edited by Doppelgänger; 04-30-2013 at 10:34 AM.
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Old 04-30-2013, 02:23 PM   #28
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Quote:
Originally Posted by Doppelgänger View Post
So what is your input on rubber vs poly for a mostly street driven car (but gets driven hard)?
Rubber is lower NVH.
Urethane handles better.

Pick one.
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Old 04-30-2013, 02:37 PM   #29
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I recommend poly bushings. easier install, and as long as they are properly lubricated you shouldn't have any noise. both Prothane and Energy kits are good and come with lube.
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Old 04-30-2013, 02:38 PM   #30
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Quote:
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Rubber is lower NVH.
Urethane handles better.

Pick one.
x2
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Old 04-30-2013, 02:52 PM   #31
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Originally Posted by emilio700 View Post
Rubber is lower NVH.
Urethane handles better.

Pick one.
So I'm probably going to guess that if I said I have a 3" catless turbo-back exhaust, Ohlins DVF coils with 12k/8k springs, and chassis bracing out the wazoo, then you'll tell me I've already tossed the NVH excuse out the window and to go with poly.....

The only NVH I'm really afraid of is something like people describe with the AWR/SuperMiata engine mounts, but I'm guessing the NVH from poly mounts isn't even comparable to that (duh).

I guess that helps me come to a more clear decision for when the time comes. Thank you Emilio.
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Old 04-30-2013, 03:28 PM   #32
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Quote:
Originally Posted by Doppelgänger View Post
So I'm probably going to guess that if I said I have a 3" catless turbo-back exhaust, Ohlins DVF coils with 12k/8k springs, and chassis bracing out the wazoo, then you'll tell me I've already tossed the NVH excuse out the window and to go with poly.....

The only NVH I'm really afraid of is something like people describe with the AWR/SuperMiata engine mounts, but I'm guessing the NVH from poly mounts isn't even comparable to that (duh).

I guess that helps me come to a more clear decision for when the time comes. Thank you Emilio.
Not even close to the same NVH increases.

I'll put $20 that you won't notice a damn bit of NVH increase in your car going to poly, and poly is what you should use.

I'm putting poly in my MSM next spring before bringing it back out for summer. It'll have about 80k miles on it at that point. I'm just that gay for poly. (Oh, and i wish i had used the AWR motor mounts instead of the Comps.)
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Old 04-30-2013, 03:47 PM   #33
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[offtopic] I love the design of the AWR/SM mounts...so much win. But EVERY review, even with the "soft" insert states that car will vibrate apart. I wonder if a "softer" rubber insert were used instead of poly, if they would be livable. [/offtopic]
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Old 04-30-2013, 08:25 PM   #34
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With your vehicle NVH changes due to suspension bushing changes will not be detectable.
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Old 04-30-2013, 10:45 PM   #35
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Quote:
Originally Posted by Doppelgänger View Post
I love the design of the AWR/SM mounts...so much win. But EVERY review, even with the "soft" insert states that car will vibrate apart. I wonder if a "softer" rubber insert were used instead of poly, if they would be livable.
As someone who personally has about 40 hours of racing with the 70 durometer versions and an 8500rpm redline, I can tell you that nothing has vibrated off.
Car buzzes but they are race mounts. If you want no buzz, stick with OEM mounts (not Mazda comp mounts). FWIW, OEM NA engine mounts are harder durometer than OEM NB mounts. NB mounts for those of delicate disposition.
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Old 04-30-2013, 11:27 PM   #36
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Interesting. I can say I learned something new. Never heard that before.
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Old 05-01-2013, 02:51 AM   #37
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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.

I have never driven a poly-equipped car, but I have heard the same thing. ES made full kits for Datsuns way back, but as I recall they were rarely used for street applications because of this.
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Old 05-03-2013, 02:14 AM   #38
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Quote:
Originally Posted by Doppelgänger View Post
[offtopic] I love the design of the AWR/SM mounts...so much win. But EVERY review, even with the "soft" insert states that car will vibrate apart. I wonder if a "softer" rubber insert were used instead of poly, if they would be livable. [/offtopic]
Mine came in yesterday. Workmenship and design is amazing! I bet they are going to feel like heaven compared to the delrins I am running now.
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Old 05-03-2013, 11:28 AM   #39
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ISC Racing uses bearings on the rear arms on the lower inner. They use Delrin everywhere else I think.
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Old 05-03-2013, 12:15 PM   #40
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Mine came in yesterday. Workmenship and design is amazing! I bet they are going to feel like heaven compared to the delrins I am running now.
Please please please please post a comparison review asap!

Dopple, I'd wager if you spend all that money and time, you won't feel a damn difference between what you have and new rubber. So if you must tackle the bushing project, go poly.
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