Not sure if the Simotoma is the same as Sumitomo, but it they are, I'd actually rate them. I've had them on going on 6 months and hav found them to be a very good bang-for-buck tyre.
I should point out the following though:
*I have 17s, not 18s, and theyre 235s, not 255s as Id imagine you'd have on 18s.
*not particularly sticky in the wet, but theyre great in the dry.
*I also get the feeling they're a pretty soft compund......Im saving already.