Today I am going to look at a set of 18x9.5 +38mm work emotions. I wanted to go with the same size tires in the front and rear so that I can rotate them but I notice most people seem to have staggered setups on SCs.
Is it mostly for stance? Or are there other benefits?

What is the biggest size tire I could run on these wheels that wouldnt rub?

 

Depends on if you are lowered and how low and if you rolled your fenders. safest would be 245/40r18 square. ideal would be 255/40r18 with around 10mm spacers in the rear but you will need to roll if lowered

 

I was considering 255/35/18 tires going off of https://www.1010tires.com/Tools/Tire-Size-Calculator as i was worried about throwing my speedo off too much. I have stock suspension but the extra sidewall on 255/40s would be nice, I'll probably go with those

 

The 255/35 x 18 is the same OD as your original 15" tires so this size would not affect your speedometer. I have this size on the front of my car but have 275/35 x 18 on the rear which are the same OD as the 16" tires on the SC400. I did put up with a slight amount of rubbing and finally decided to have the wheel opening cut back a little and now have no rubbing. Of course my car is lowered and I love it.
Bill