I had them siped because all those little edges are supposed to grip much better in rain/snow/ice and we get all three here in OR. It was very cheap, $5-10 per tire. I don't know about the difference it makes, as I had it done when I bought them.Rob Mayercik said:Motornoggin - may I ask why you had them siped, and if there was an appreciable difference after doing so?
Rob