Tyres and suspension

[Hornman!]

Hi, just bought my first Z4, have been toying with the idea for years, but when an affordable 23i became available, couldn't resist. However, not happy with the ride quality - too twitchy and jarring. Having investigated the forums decided to replace the run flats with standard tyres (while refurbing the alloys) - did improve the ride a bit and got rid of some of the twitchiness but not as much as I hoped and the jarring ride is still there. So I have 2 questions:

What tyre pressure should I run the Goodyear Eagle 225/45 R17 91Y at? Tried at same settings as run flats (2.4/2.9) and just today started trying 0.2 bar lower - so far another small improvement? So what would you recommend?

Also thinking of replacing the suspension: currently coming down to 2 options Bilstein B12 Kit - £527 + £400 fitting OR KW version 1 - £1300 fitted. Read good things about both kits but is the KW worth the extra? How does the ride on these compare to standard? (Road use only - mostly on the poorly maintained ones in and around Norfolk!)

[Busterboo]

Are jarring and twitchiness inherent problems with 17" wheels like yours? I didn't think so. And 2.4/2.9 bar pressures shouldn't make them so.

Therefore, do the causes lie elsewhere?

[flybobbie]

I found the quality of my 23i shocks to be rubbish and replaced them with Bilstein B6 with Goodyear asymmetrics.
I run psi 40 rears and 38 fronts and have even wear across the tyres. But you won't get a saloon car ride.
Later i moved from 17 to 18 inch which made no difference to the ride, just the looks.

[Silverzedtom]

Time for new bushes perhaps? Springs and shocks ok? When’s the mot? I’d give it the once over, or have someone else take a look before dropping money on parts. Even the e89 will be needing a few replacement bits and bobs now.

[Tinker15]

What are you comparing your Z4 ride with? If you can it may be worth trying another Z4 before you drop large amounts of money trying to correct something that is inherent to the model.

[Hornman!]

Thank you all for your comments - Tinker15 - I'm comparing this to my previous Z3 with 2.2 v 2.5 engine. Busterboo and Silverzedtom - Good advice about checking elsewhere - bushes etc. before investing (will do) and flyboobie for specifics about alternative shocks and pressures - as they are my tyres will give that a go. (B12 kit I think includes B8 shocks)

Will let you know what happens next!