I have been regrooveing my tires for years, no problem at all..... Until now.
I was getting a level one in California (of course) and CHP guy said that I need the same number of grooves that the factory put in the tire. HUH? I run FS-591's and they have 6 #10 grooves in them (not counting the decoupler), I have always ignored the grooves that are a half inch from the middle grooves so I just do four grooves evenly spaced across the tire with the same #10 (3/8 wide groove) as the factory. The cop didn't cite me but said I had to do all 6, I didn't demand he show me the regulation just in case he was right, he probably would have gone ahead and written it. Does anyone have real actual black and white clarification on this?