My 08 plated 1 series came with run flats. The ride was firm but since my previous car was a Mini Cooper with run flats I considered it OK, in truth it was much better than the Honda Civic I tried without run flats. When I fitted winter tyres they were non run flats and the difference was incredible, much smoother and possibly quieter. Insurance company was happy. Before selling the car I asked the insurer if I could use non runs flats for summer use as well, the answer was yes providing you don't mix run flats and non run flats on the car, no extra cost.

I simply carried a bottle of goo in the boot I bought from Wilko's in case of a puncture.

BMW will tell you to use only run flats plus they will also insist they are the BMW approved ones since they probably make more money on those. Mine went in for a service/MOT and a couple of warranty items when the non run flats were fitted and they never mentioned anything about them. In fact if you buy winter wheels/tyres from BMW they will be non run flats.

When I swapped the BMW I was interested to spot that some models are now fitted with non run flat tyres as standard, the run flats are extra. Guess which i would have specified if I had bought another BMW.

so he has replaced with runflats with the BMW logo otherwise his insurance company have said the car would not be insured.

That may be the case with your sons insurance company but not all take that view. As with any modification you need to tell your insurers, some will charge, some will not but it can pay to shop round to see who is the most agreeable to your needs.

Agreed his is a specialised car but most insurance companies will ony insure the car if you use wheels and tyre size listed in the car manual not telling them is one way but if you have an accident the loss assessor normaly checks as a matter of course the wheel and tyre size.

As I said in my post above I informed Aviva about my change to non runflat Winter tyres on 16" instead of the standard 17" wheels and there was no charge. There was also no charge for using non run flat 17" tyres for the remainder of the year. Both the 16" and 17" sizes were as listed in the manual.

Different insurers may have different stand points but Aviva were very accomodating with my requests, they only charge more if you go bigger than standard I believe.

When I had my car checked many years ago by an assessor the tyres were one of the first things he looked at so I am fully aware they check after an accident (which in my case was being hit by an out of control motorcyclist). That is why I checked with Aviva before spending, there is no way i would risk driving an uninsurred car.