hi can any one tell me the best rear tyre/size to fit on my vfr400z. its got a 130/80 18 pirelli sports demon on at the moment .will a 130/70 tyre fit

I'm not an expert on tyres but my NC21 had a 130/70-18 Bridgestone BT45 when I bought it (with a matching 100/90-16 on the front), and I was really happy with them.
I think 130/70 is the standard size, so your Pirelli is oversized.

As above Your pirellii is wrong, the sidewall is too tall.

100/90-16 front
130/70-18 rear.

They are the correct sizes