What Does The Writing On The Side Of My Tyre Mean?

In this photo we have a 180/55 ZR17 (73W) tyre, whichmeans it’s 180mm wide, and the profile height is 55% of that, so 99mm. 
The 17relates to the rim size – 17inches – while the 71W is the speed and loadrating; 365kg and 168mph (270kmh). Because that rating is in brackets, it meansthe tyre is capable of speeds above the figure, but if there were no brackets,it’d mean the rating was the maximum. 
The ‘M/C’ simply denotes that the tyre’sintended for use on a motorcycle. You can also see the direction of rotation –if this is the wrong way round, your bike will fail its MoT.