Yeah, same here . It is a little 911 From 98. I use it for running around town and to go to work, so was hoping I can just use those shit tyres wheel come with for now.
It's not so much any insurance accessor that I would worry about, but the Police. If you are involved in a serious accident, serious as in there is a human serious injury, then the Police do look at tyres when they do a report that insurance companies can get. They can't get the report if there is a prosecution until after that is dealt with. I know that they went over my bike even though I was the innocent party. I can't remember what size back tyre I had but I've been known to fit "wrong" sizes where I've read reports of better handling with the different sizes. Now, for whatever vehicle concerned - car or bike - I would be reluctant to change tyre size.
Just to confuse you more, Pirelli appear to recommend 265/35R18 on the rear of a ‘98 911? https://www.pirelli.com/tyres/en-gb/car/products
I believe the insurance companies are more concerned with the speed rating of the tyre, non-standard sizes of the correct speed rating are ok if they pass MOT. for MK2 Escort rallye stylee having the back lowered looks cool - for street racing Porker you want the front slammed but at 8mm you will not really notice. As you say you are not looking to be a track hero but more a daily sensible drive so if I was you I wouldn't be concerned but it is obviously how you feel about any perceived risk in your own mind. Wheels will fit a number of sizes of tyre but are most suited to a specific size - a 6" wide rim will take a 205 tyre but it would sit better on a 7" rim
