Polybushes - Any Good?
Discussion
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 , but I can see why other people might want to go the polybush route to get what they want from their car...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.
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?
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.
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.
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.
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. Surely the resistance of the rubber bush pushing back against the movement increases the hysteresis.
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.
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)...
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.
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?
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%.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%.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
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
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