Originally Posted By: bvance554
I've had it done on passenger and M/T tires and it works very well. They do not cut deep, and in no way does it harm you're tire. the naysayer arm chair expert tire guys with zero experience here really shouldn't comment.
Being an actual non-armchair expert, I guess I'll comment.
Does it work? Yup. Cutting new sipes will give a tire some more snow grip. Absolutely. It comes at the cost of increasing tread squirm, tread wear and chunking, because the sipes let the tread block flex in ways it was not designed for. The thought of it pretty much makes tire engineers shriek like little girls. As others have noted, siping technology has already gone way beyond simple cuts and into having a complex 3D topology inside the cuts that let the engineers determine exactly how much flex to allow, which decreases the squirm and drang of it all.
So I won't deny that it works, but there are tradeoffs. It will absolutely void any manufacturer's warranty, and I note that Schwab's warranty says nothing at all about siping.
Schwab's site also states that siping increases treadlife because the sipes reduce heat generation, which is IMHO, [censored] because a) heat generation is not generally a problem in the snow and b) that's not enough to overcome increased wear caused by squirm.
So I personally wouldn't do it, nor would I recommend it. You're better off with siping that has been designed into the tire. On the other hand it probably won't kill you, and it does work in a sense.