Subject: why are tyres measured in metric/imperial??

hello,
i dont know how it works in the US but over here all car tyres are 
measured using both metric and imperial units, ie, 205/50/16. that is 
205mm tread width, 50% aspect ratio and 16" diameter wheel, this is even 
used in mainland europe where they have not used the imperial for many 
years.
i hope you can help as this has intrigued me for a long time
cheers james 

Re: why are tyres measured in metric/imperial??