Which polybush's to buy?

[Chezsherman]

My 2007 z4 has just had a MOT which passed but one thing was mentioned about the wishbone bushes are worn. So have been looking at replacing them with polybush's to stiffing things up for the start of forum meets I take part in.
My question is which ones to buy? Been on the power-flex website and there are 2sizes 60mm and 66mm?, also what is the difference between to normal bush and the aluminium outer?

Thanks in advance
Chezsherman

 

[GuidoK]

You need the 66mm
They claim that the aluminium outer shell deformes less and has less friction. Imho thats BS. Friction in the bushing is not an issue (the 1 or 2 kgm of friction is nothing compared to the tonne of foce the spring endures), and the deformation maybe (although the normal black outer shell is really hard (shore95A), but that is the same effect as a stiffer bushing. I doubt the difference is noticeable as the majority of the compliance of the bushing is determined by the softest part, and that is the purple piece (and that is the same).

They also have the 'Black series' (competition) which is I guess all shore95a stiffness (so that is stiffer).

To get an idea: the purple rubber is shore80A, which you can still deform with your fingers (it feels like rubber, maybe a bit on the stiff side compared to automotive rubber, but compareable), but shore95A already feels like plastic.

So I don't see a real objective reason to get the aluminium ones (but I also don't se a negative). Maybe the are an easier fit in the lollypops (I don't know if they are press fit), but you can also get the normal ones prefitted in the lollypops for an extra fee on ebay.

Some more info in this thread:
http://www.z4-forum.com/forum/viewtopic.php?f=2&t=72676