@NemesisUK Thank you for the calculator.
Yes - I am proposing to replacing stock 215/45 R17 with 225/50 R17.
Looking at the calculator, if I was showing 70 mph, then my actual speed on the new proposed tyres would be 73.53mph, so under the definition of the law this is not allowed - but aren't cars speedo's calibrated to over report the speed by a certain %? I will be checking with my insurance company to ensure they are happy with the 'mod'.
Question is - has anybody else changed their tyre sizes away from the stock size of 215/45 R17? I have read another thread on this forum someone did this and noticed a huge improvement in the comfort.
Or - I can just stick to the normal size when I change the tyres :).