Hello Simon, The tyres you have fitted should be fine. The ST4 and the ST4S use that section rear tyre.If anything the bigger rear will slow the steering.(so MCN says).The rr's will take a little longer to warm up than the standard 207's but once warm will give more grip.(ask Jools)
I run Standard 207's on my ST4 and find that give good grip last well and can be had for good price when bought in pairs.
I'm sure they used to be a section on the ducati.com web site reguarding suspension set up, but iv'e looked and cannot find it if i do find it i'll let you know.
You could have a word with jools he's done most things to his ST2 and that goes round corners as if on rails.(but not at rockingham)
