I'm looking (on behalf of someone else) for a spare alloy for a Vauxhall Astra DTi (2001) - unfortunately I don't see sizes, or don't understand, what's written on the existing tyres. Could someone assist a complete idiot in finding a spare please? I don't wish to buy a set though. Basically I need to know how to gather the information to go find one. I have photos, details of what's written on existing tyres, uk reg certificate with all motor details on it.