I had stock 189s with Hankook Ventus V12s (245/35 front; 265/35 rear). I just purchased a square set of Kosei K1s (17x8.5 ET40) with 245/40 Star Specs all around. Stock sport suspension on E92 335i RWD, pins removed, max neg camber at around -1* front, -2* rear.
The difference in the amount of grip is shockingly different even at low speeds. It only feels slightly quicker at lower speeds due to lighter weight, but not much difference as I expected. Despite taller tire sidewall, the tires are very stiff and I'd say they do not compromise steering response, if not better (hence harsher ride). On the other hand, I don't know how, but the steering quickness is now similar to an M3 (smaller steering input, larger output). Perhaps it's due to square setup, grippy tires, or another reason. Whatever it is, it almost caught me off-guard in the highway trying to dodge a pothole. Steering effort is higher. Road noise is quite a lot more, kinda drones during highway speeds.
I know that the stock sport wheels I had were 18x8 ET34 front; 18x8.5 ET37 rear. Which means, now I have about 12mm LESS clearance from inside of the front wheels to the strut, and 3mm LESS in the rear. So far, I don't hear anything rubbing, but I'll have to check if there's any rubbage on the strut. I did, however, test that I could barely stick a cardboard paper between the front strut and the rim. Well, as long as this is not gonna rub, I'm fine with it.
Because of the new offsets, it is my belief that the suspension geometry has changed. The center (of force) of the wheel has now gone more inside due to more positive offset, and I think a few things have changed as the result:
1) car sits higher due to shorter moment arm of car weight pushing the tires up around the control arm joints
2) steering effort is more
3) turn in is fast (could be good or bad)
4) other handling dynamics probably have changed
Should I get spacers (6mm front, 3mm rear) to replicate OEM offsets? And ultimately would this relieve the changes I feel now? Or should I just embrace the new feel of the car because the are "improvements?" If rather I should get the spacers, what brand and where can I buy them from?
I don't care about car height in terms of looks; I only care about handling dynamics, performance (whatever that means..), predictability, reliability; I believe in OEM/BMW engineering for the most part; I will be tracking my car a LOT, during which my rims, hubs and suspension parts will undergo a LOT of stress
Sorry for the long message...... Thanks for your expertise!