expiry of Tyres

Tyres have a four year validity period from the date of manufacture. A stamp like *2507* asterisk at the beginning and end of the serial number.
First two numbers represent week of the year in which tyre was manufactured.
*2507* means the tyre was manufactured in the 25 th week of the year 2007. The expiry date will the the 25 th week of 2011.