Polybushes - Any Good?

Author
Discussion

CoolHands

18,496 posts

194 months

Monday 4th December 2017
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So basically, stick with OEM rubber

Ps surprised no ones mentioned this, but if solid plastic bushes are so great why don’t manufacturers fit them. In my opinion polybushes are nonsense.

Gojira

899 posts

122 months

Monday 4th December 2017
quotequote all
CoolHands said:
So basically, stick with OEM rubber

Ps surprised no ones mentioned this, but if solid plastic bushes are so great why don’t manufacturers fit them. In my opinion polybushes are nonsense.
I'm getting close to retirement, and my back won't forgive me if I put polybushes on the Insipid biggrin, but I can see why other people might want to go the polybush route to get what they want from their car...

There probably aren't enough people on good terms with their chiropractor for it to be worth mainstream manufacturers building cars with polybushes from day one, but if people want to fit them what's the problem?

E-bmw

9,105 posts

151 months

Monday 4th December 2017
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I am sure there are many reasons, here are a few that spring to mind:

Poly bushes cost more & pretty much #1 on the list of criteria for the bean-counters who (ultimately) build cars these days is cost/profit.

They are more likely to fail/wear & therefore (hopefully) this will be sorted out at a franchised dealer who will use oe parts resulting in more after sales.

They are at least a degree more compliant & therefore make the car a little quieter to drive & that is more important to more of the average men in the street.

Or at least so the cynic in me says.

E-bmw

9,105 posts

151 months

Monday 4th December 2017
quotequote all
JoeMk1 said:
especially after a few months when the grease is no longer effective and the metal tubes have corroded
They are made of stainless steel.

They are in every one I have seen anyway.

E-bmw

9,105 posts

151 months

Monday 4th December 2017
quotequote all
JoeMk1 said:
Therefore, the vertical wheel Force/Displacement curve will have more hysteresis with polybushes than rubber bushes.
I don't see how it has more hysteresis.

Surely the resistance of the rubber bush pushing back against the movement increases the hysteresis.

GreenV8S

30,150 posts

283 months

Monday 4th December 2017
quotequote all
Polyurethane comes in varying grades, and so does rubber. OEMs put a lot of effort into optimising their bushes for handling and NVH. It may be that their compromise doesn't suit everyone and some people want stiffer or softer bushes. In that case, a poly bush might suit them better than the OEM. However, I suspect that many of the poly bushes aren't optimised at all and are just a blob the right size and shape which people will buy because poly is all motorsporty and expensive so it must be better. The poly bushes I've seen have actually been quite soft relative to the OEM rubber bushes they're replacing. They might last longer, but I wouldn't assume they're going to work any better.

JoeMk1

377 posts

170 months

Monday 4th December 2017
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E-bmw said:
I don't see how it has more hysteresis.

Surely the resistance of the rubber bush pushing back against the movement increases the hysteresis.
Hysteresis in this instance is the difference in force at the contact patch when moving the wheel up vs down. When I push the wheel up, I don't yet have hysteresis, until I move the wheel back down. The friction in the polybush holds the wheel up slightly as it moves down, reducing the force relative to on the way up, creating a difference in the contact patch force when moving the wheel.

The resistance you are referring to is the bushes contribution to the wheel rate, which is another factor that changes with polybushes vs bonded rubber bushes.

Lewis's Friend

Original Poster:

1,026 posts

189 months

Thursday 7th December 2017
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Cheers for all the info chaps. I think I'm going to stick with OEM bushes. Partly as these seem to be the best fit for what I'm after, and partly as polybushes on Mx5's seem to be rather a fraught subject, with stories of snapped wishbones with improperly fitted polybushes (in extreme instances I would imagine)...

SebringMan

1,773 posts

185 months

Monday 11th December 2017
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The only poly bushes worth getting are the SuperPro/SuperFlex bushes, nothing else. The rest are cheap crap. There's a great YT video of this.

Otherwise, go to MX-5 Parts and get genuine bushes. The dealers IME are hopeless and don't care much for the old tin.

sgtBerbatov

2,597 posts

80 months

Wednesday 13th December 2017
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E-bmw said:
JoeMk1 said:
especially after a few months when the grease is no longer effective and the metal tubes have corroded
They are made of stainless steel.

They are in every one I have seen anyway.
I refitted the front bushes on my Corolla with polybushes, all came with stainless steel tubes.

It's been a few years since I studied chemistry, but as far as I know stainless steel has little to no iron within it to rust. So they don't corrode?

Mignon

1,018 posts

88 months

Wednesday 13th December 2017
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sgtBerbatov said:
It's been a few years since I studied chemistry, but as far as I know stainless steel has little to no iron within it to rust. So they don't corrode?
I guess you didn't learn much then. Stainless steel is primarily iron as are all forms of steel. Stainless has a high concentration of chromium in it though which is what prevents corrosion. A minimum of 10% and up to 28%.

sgtBerbatov

2,597 posts

80 months

Wednesday 13th December 2017
quotequote all
Mignon said:
sgtBerbatov said:
It's been a few years since I studied chemistry, but as far as I know stainless steel has little to no iron within it to rust. So they don't corrode?
I guess you didn't learn much then. Stainless steel is primarily iron as are all forms of steel. Stainless has a high concentration of chromium in it though which is what prevents corrosion. A minimum of 10% and up to 28%.
You might be right that my knowledge on the composition of metals is a bit wrong, but I know stainless steel doesn't corrode. And for the subject matter at hand, that's all that matters.

GreenV8S

30,150 posts

283 months

Wednesday 13th December 2017
quotequote all
sgtBerbatov said:
I know stainless steel doesn't corrode
It does corrode, but it corrodes less quickly than mild steel - how much less would depend on which grade of stainless it is.

sgtBerbatov

2,597 posts

80 months

Thursday 14th December 2017
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GreenV8S said:
sgtBerbatov said:
I know stainless steel doesn't corrode
It does corrode, but it corrodes less quickly than mild steel - how much less would depend on which grade of stainless it is.
But will it corrode quicker than a normal rubber bushing perishing?

Flibble

6,470 posts

180 months

Thursday 14th December 2017
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sgtBerbatov said:
But will it corrode quicker than a normal rubber bushing perishing?
Depends on the grade of stainless and the environment it's in. Put low chrome stainless in a salty environment for instance and it'll corrode plenty fast.

The Dangerous Elk

4,642 posts

76 months

Thursday 14th December 2017
quotequote all
The only place I would use polybush's are in Non-Direct-Suspension (for want of the correct term) connections such as Anti Roll-Bar joints/Drop Links etc. For joints such as wishbones, swing arms and spring bushes I always use OEM rubber.

Alex

9,975 posts

283 months

Thursday 14th December 2017
quotequote all
I am not a fan of polybushes on a road car. They make the suspension noisy and crashy and tend to wear out quickly, in my experience.

SebringMan

1,773 posts

185 months

Thursday 14th December 2017
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Alex said:
I am not a fan of polybushes on a road car. They make the suspension noisy and crashy and tend to wear out quickly, in my experience.
You've been using the wrong polybushes wink.

Lotobear

6,232 posts

127 months

Friday 15th December 2017
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I fitted Autobush polybushes to the rear of my 1970 Lotus Elan and Superflex on the front.

10k miles later they had worn oval in the bore. I've switched back to metalastic bushes and the ride and handling quality is better and I expect them to last much longer.

Personally I would never use them again. The manufacturers generally get it right IMO

MiniCooperYes

1 posts

75 months

Friday 15th December 2017
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SebringMan said:
Alex said:
I am not a fan of polybushes on a road car. They make the suspension noisy and crashy and tend to wear out quickly, in my experience.
You've been using the wrong polybushes wink.
You need those rubber polybushes wink