Our regional tire store likes to offer siping of tires (that they do to new tires) for an extra $10 a tire. This is in western Oregon where we get lots of rain but not much below freezing driving. Is it worth the extra $$?
It should help some in the rain and a little more in the snow or ice. It also is known for reducing tyre life. It’s up to you.
Excellent way to void any warranty on your tire too.
If your tires are rated for good traction, don’t bother. If they are a poor traction tire, buy the better tires.
Siping was a way to provide better slippery surface traction in the old days. It worked well. Molding technology has advanced since then. Numerous models of tires now come out of the mold with lots of good edges. Siping is no longer necessary and can in fact have an adverse effect.
When you go to the tire store, look at Blizzaks, Michelins, and other good snows. You’ll see that they already have slits in the tread blocks. But where you livs a good all season tire would probably be more appropriate anyway.
All “all-season” tires are heavily siped from the factory. Save your money.