I am a big believer in intelligent siping. (Not going crazy with it.) In fact, I did it last night to my personal vehicle to get a few more miles out of the treads. I absolutely think, especially on bigger tread truck/4x4 tires that it helps.
That being said, I'd never do it on an R.O. I know some tire shops out there that will - but it just seems like a big risk to me. Not just from some freak of nature accident, but more from the tire chunking if it isn't done right.
I'll show a customer what it is, lead them to a website or two to explain how to do it, maybe even lend them my 1/4" depth-set razor blade - but I'd never do it professionally.
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