Siping is quite common in heavy commercial applications -- like tractor trailers, etc. Decades ago it was common for the consumer market -- now dedicated snow tires have replaced siping. I'm frankly surprised Jim could even find a shop that would do it. I'm certain any warrantee is now void... not that that's any real big deal on a set of tires.

If you look at modern snow tires, they're all siped in one fashion or another. The Michelin "Arctic Alpine" (or some such thing) is the most noticeable. The tire has a very mild, non-aggressive tread. To look at it, you would think that it would be awful in snow. But the sipes that are designed into the tread apparently make it a very good ice and snow tire.

jp
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Jeff Pierce (Post back with your results... it's what makes this forum work.)