Tyre choice is always so subjective (as this thread and many others before it prove).
There are so many variables.....
* car set-up - suspension: OE or aftermarket
* geometry
* wheel choice - diameter/width/weight/offset & resultant impact on cars track width
* tyre pressures
* tyre condition
* driving style
* use (road/track)
* surface
* temperature
* weather conditions
* expectation & experience
* ability to accurately evaluate and compare
At the end of the day if you have found a tyre that you like and gives you confidence, that is what matters.
For what it's worth, I really rate the OE conti's for road use (not yet tried them on track) - I think for the road they are brilliant. But that is my opinion, on my car (which is no longer std.) and reflects my driving style and expectation of a performance road tyre.
I also have fitted the BMW retro fit strut brace which has helped my front tyres better key into the road on medium & high speed corners and offers more feedback from the front end. It works for me on my car but may not suit the next guy with a different driving style, set-up, or expectation...
The general concensous of those adept in the "black art" of suspension tuning will say that if a manufacturer has developed a car on 18" wheels putting 19's on will not likely improve the handling, they will probably have the opposite effect (as some of you have found)... Mine is on 18's.
I wanted handling over looks - Again to each their own (there is no judgement here...)
Going smaller in diameter than OE, given the alloys are lighter, can further improve accelleration, handling, feedback, turn-in speed etc.. due to reducing unsprung weight. But to really get a discernable improvement here, this mod inevitably will require signifcant suspension tuning by someone who knows what they are doing (potentially new adjustable shocks & springs & geometry tweaks) to dial everything in to make positive use of the reduced rotating mass (unspring weight) - The benefits of this mod has to be weighed up against the cost (if new suspension parts are to be purchased) & potential reduction in brake disc size (I don't know if OE discs & calipers will fit under 17's), then likely reduction in brake performance/overheating if disc size is reduced (unless you then fit cooling ducts and pipes for the brakes, like race cars).
Might be worth it for a track/race car but most would see it as a bit extreme for a road car where the benefits on road couldn't really be fully exploited anyway...It makes more sense to go for light weight 18's - OE shocks and springs can release benefits here.
There are choices aplenty depending on what you want and like... "life is like a box of choc's"
