biggest size for 13 inch truck tyres?

[gemery10]

Ok. I don't do any serious 4wd but used to have 14 speedies on an unlifted subaru and prefferred gear ratio from bigger wheels. They had massive camber issue so I swapped with a shop for 13 inch alloys (really pretty ugly but oh well). Questions is with 13 inch rims what truck tyre will not scrub in an unlifted l series with kingsprings in rear? (my speedies didn't)

my guess is
175 80 r13 = 610 (same as 195 65 r14)
185 80 r13 = 626

Also are truck tyres a nghtmare in the wet?

any help would be great as the 185 70's are on their last legs