Polyurethane and eurethane - are they the same

[BigKriss]

From the UCC mailing list;

> Here's one for all you armchair racers who think that Eurethane is
> something that should be installed on a vehicle.
>
> An example of E34 Eurethane thrust rod bushings after only a few
> thousand miles. http://www.koalamotorsport.com/thrustrod.avi
>
> The single biggest thing you can do to downgrade your stock BMW
> suspension is use Eurethane bushings. I've said it for years, but now
> I have video proof, bad as the video is.
>
> Brett Anderson
> KMS

Found this link today from Brett Anderson (Koalamotorsport). Shows a thust arm which is in bad shape. I'm thinking of putting on polyurethane bushings (both lower and upper arms). Any thoughts guys?

[epj3]

I think they ment urethane... I've never heard of "eurethane"... but urethane (aka polyurethane) is tougher than the rubber or grease filled rubber bushings bmw makes OEM for our cars... not sure what they are trying to say.

Plus, urethane bushings don't have to be preloaded like the oem bushings do. Personally I'm going with the gruntsbushings.com urethane control arm bushings.

[Jon K]

I think they ment urethane... I've never heard of "eurethane"... but urethane (aka polyurethane) is tougher than the rubber or grease filled rubber bushings bmw makes OEM for our cars... not sure what they are trying to say.

Plus, urethane bushings don't have to be preloaded like the oem bushings do. Personally I'm going with the gruntsbushings.com urethane control arm bushings.

The point is that the OE bushings do have some play in them being rubber, the urethane do not and they seperate from the control arm... easy to follow.

[epj3]

The point is that the OE bushings do have some play in them being rubber, the urethane do not and they seperate from the control arm... easy to follow.

Oooh I see what they are saying now. So, really, should I go with M5 bushings over urethane?

[Rory535i]

they seperate from the metal because they don't have the same bonding properties as rubber...

[Mobius]

Plus, urethane bushings don't have to be preloaded like the oem bushings do. Personally I'm going with the gruntsbushings.com urethane control arm bushings.

ANY thrust arm bushing needs to be tightened at ride height. This isn't preload; you're preloading the bushings if you're tightening them with the wheels hanging down.

They need to be tightened at ride height in part because the inner metal sleeve of the bushing can not rotate in its mount - and if it could, you'd eat up the thrust arm mount in no time.

That said; I believe polyurethane bushings, especially in the thurst arm, belong only on strictly track cars (and not for you "oh lol my car is a track car FOR THE STREET" people, either). The TA bushing needs a certain amount of flex to protect other suspension components from damage. If you use a hard bushing here, you're only shortening the life of most other components of the front axle. If you look at the stock bushing, there's a LOT of design in it - there's none in a poly bushing.

Not to mention the fact that I wouldn't be surprised in the least if most of the people who peddle poly bushings online are anything more than people with some pipe and a can of liquid polyurethane in their garage. The bushing in the video certainly seems to have been made in this fashion.

If you can find quality, properly built poly bushings, then they can be beneficial in certain applications. However, even a quality poly bushing does not belong in the thrust arm - in my opinion. Shitty, 'home made' poly bushings (like those in the video) belong nowhere.

[niall]

(and not for you "oh lol my car is a track car FOR THE STREET" people, either).

thats very opinionated. and not true in all cases,
lots of people prefer stiff suspension and poly bushes area great way
to go, what other suspention components do you think you are shortening the life of? i totally dissagree, i think poly bushes do a better job than factory stuff . as for the design side, id say very little goes into the design of a rubber bush. there is no science here guys.

[Mobius]

thats very opinionated. and not true in all cases,
lots of people prefer stiff suspension and poly bushes area great way
to go, what other suspention components do you think you are shortening the life of? i totally dissagree, i think poly bushes do a better job than factory stuff . as for the design side, id say very little goes into the design of a rubber bush. there is no science here guys.

********. There's a TON of 'science' and design in the TA bushing; have you looked at one? There's a reason BMW makes so many different versions of the same bushing.

Through the movement of the front suspension, the TA bushing is forced (and designed) to flex. If you disallow this flex, you move undue stress to the TA ball joint, and by association, the lower arm ball joint and bushing. Also, though I haven't heard of it happening on an E34 - I've seen a couple instances where replacing bushings that are intended to flex with hard poly bushings causes metal fatigue and the eventual destruction of the bushing mount. See here.

Anyhow, we've had this discussion before: http://www.bimmer.info/forum/showthr...2&page=2&pp=10

I'm not saying polyurethane bushings are ALWAYS bad (in fact, they're probably fine for most every other bushing in an E34's suspension); but they're a poor choice for the thrust arm - in my opinion.

[niall]

well my bro is getting them in his e34 so i gues time will tell, and ill know first hand then if that is the case

[Anthony (M5 in Calgary)]

Oooh I see what they are saying now. So, really, should I go with M5 bushings over urethane?

Stiffer than the 750 bushing but still compliant enough for the street. Not hydraulic either.

Anthony