The great suspension bushing debate- rubber or poly...
#21
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.
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.
#22
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.
#23
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).
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).
#25
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.
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.
#27
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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)?
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.
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.
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 09:34 AM.
#31
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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.
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.
#32
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.
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.
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.)
#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]
#35
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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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.