[400TT]

Plenty of online wheel/tyre size calculators. Just Google "tire calculator" etc. They do vary slightly between manufacturers though, so for the exact spec's see the manufacturers web site.

16" tyres are really limited in sizes(especially wide sizes) & pricing is often poor, that's the downside. But they are a great compromise for looks and performance. A lot of Cobras are fitted with 16" wheels. My GT40 originally had 16" wheels.