Will be changing the tyres on my cup soon and from previous experience 6 years ago on my Mk1 16v i had coilovers on which transformed the handling. I then added 16inch (17inch rubbed) TSW wheels and 215/40 tyres Yoko A520 at the time. Grip was too another level and the handling / performance etc was not compromised.
Has anyone done this on their cup as i have Eibachs on now and im planning to put the 215/40 on the standard rim.