big_al i got the original 135r12 size for mine, and they were AU$75 each. i went to a specialist wheel shop, not a tyre shop, they ordered them in overnight. otherwise yeah, 155r12 tyres are on my friend's niki cos they were cheaper and he had trouble finding some 135s, and it drives perfect, even steers better for some reason, i cant figure that one out.
btw, the 12 is the rim size.