I've kept the original springs that are currently on there, tbh i couldn't hack the car being any lower than it is which is the main reason i haven't changed mine, if i could get aftermarket without lowering i would have.
(likewise those are B4 shocks, maybe should've spring the extra 100 for b6's but was rushing to get them ordered, and read b6's would be stiffer again which i'm happy to do without, ride is harsh enough on the z4 )
my Tyre wear was sorted for me this morning, ironically got not one but two punctures on same side on way to work..
switched the 225 fronts for 235's and got the rears changed as well.
Hankook Ventus S1 Evo2 on all corners, hopefully last me longer than the Pirelli