Thanks Newbie!
Why do they make car wheel arches so HUGE these days? 18 inch wheels, and they look almost small!
If I changed from my 225/45 R17 I'd probably go 235 or 245/40 R18 - the current boots look a bit thin in relation to the car and the size of the wheel. Perhaps that would fill out the arches more than the ones in the picture, without deviating too much from the circumference of my current tyres.