WOW! I replaced the Bridgestons RF (run flat) tires, with Michelin Pilot Sport ASXL. The ride with the sports suspension, improved significantly, and eliminated the jolting, without compromising the handling. As a bonus, it may enable me to use the car year around in Upstate NY, without having to invest in snow tires, and if I can get even close to the projected 40K miles tread life, I will be even happier.
It's actually my first time writing a review on a car, I was looking for a sport cart 8 months ago. My first choice was a Porscha Cayman S with a manual transmission. I am not going to bring back the whole Porscha vs BM discussion but let's say you will have to try the car to know what you really want. I did love the Porscha but couldnt resist to test the Z4. My only concerns about the Z4 was the look and I really didnt like it in the beginning cause all I could find here in Canada was SoftTop Z4. The driving experience of the Z4 3.0Si was magic yes I said it MAGIC. You do feel like you're driving a beast, nervous and everytime you step on the pedal you get the "push" of adrenaline...
The standard suspension may be the better choice for most people. I have only 300 miles on the manual transmission coupe, and really enjoy it, but I will install all season ties when I have to replace the OE tires. This may soften the ride and extend the time you can drive the car in the Northeast before installing snow tries.
I purchased the coupe off the showroom floor with the sports suspension package. The roads in Northern Illinois are not the best so my wife refers to the Z4 as "the donkey cart". Regardless it is a blast to drive and I get many compliments on its appearance. The dealer experience has been outstanding.