Go to a tyre dealer who knows what he is talking about,
and get him to match up tyres front and rear with the closest
possible overall rolling diameter, my local dealer sells toyos and they do
a good booklet with a the various different profiles and rolling diameters
i would think that if you keep the diameters within 5-10mm you will
be OK, thats the kind of difference you would get between a new
and a worn tyre anyway.