[Coi]

Hello and welcome. My recently-acquired Z4MR is in need of both FCAB and RTAB so I've been looking into some options. Because it's a street car I'm going with mild PU FCAB and OEM RTAB w/shim kit, so I can't speak from experience on what's good for track.

Most important things to know are that Z4M uses offset FCABs and shares controls arms with E46 ZHP, not E46 M3. This limits choices because many options wrong size (those for m3) or are not offset (those for e46 non-M). Many websites will list centered bushings are compatible with Z4M but this is not correct. A non-offset bushing will cause loss of caster, obviously not acceptable for a track car.

In terms of polyurethane, Powerflex seems to be the most popular choice. Most people seem to have positive impressions but one forum member did have it fail due to track use. Lots of people have these on their track cars without issue though. I'm going with Whiteline pu offset bushings on my car even though there aren't many reviews out there. They're a very good price and I know people who are happy with WL bushings on other cars. They're not even as stiff as powerflex so maybe not the best for track. Other options include Condor Speed offset bushings, which I guess are technically UHMW rather than PU if that makes a difference.

There aren't many options for solid bushings with spherical bearings that fit our cars. Need the bearing because the control arm rotates inside the bushing. The only option I saw are the SLR Speed adjustable billet lollipops. These might actually allow you have more caster than possible with a normal bushing, but it's also another adjustment you'll have to factor in to your alignment. I've not familiar with this company or the quality of their products, so maybe that's worth looking in to before purchasing. There might be other options available if you search more.

Edit: Just wanted to update and say that I decided against the Whiteline poly offset FCAB because I'm worried it reduces caster compared to the OEM Z4M bushing. (Forums say the Z4M bushing increases castor by 1 deg compared to a centered one but Whiteline claims theirs only does so my 0.5 deg. This could result in my caster on my Z4M being reduced by 0.5 deg. Now this may not actually be accurate but no one seems to actually have bought or reviewed the offset Whiteline to say otherwise.)