I wouldn't go below et40 (sub40), but that's just me. Best for you to try fitting spacers. Start w/ 5mm & go thicker til you get the stance you desire.When you say sub40, what exactly does that mean? Is the 40 combined total of both wheels? In other words, referring to 20mm each side? Sorry, I'm new to the slang and lingo. So maybe 15mm is the way to go? I'd be open to rolling the rear fenders. What would you recommend on the front, 5mm or 10mm? thanks.