In reply to Dan1898:
> So after realising my wife bless her cant use a tape measure, we have now worked out:
>
> 5'8 or 173cm
> 31" Inside Leg
>
> Which according to my sourced information =
>
> 17", 17.5", 18"
>
> 43cm, 44cm, 45cm, 46cm
That sounds more like it. 20" is a BIG mountain bike.
Whilst conventional wisdom says look at the frame first of all at your budget some bikes will have woeful forks which can wreck their ride so check fork reviews too.