Siping tires dramatically improves tire traction by improving the tire’s ability to “grip” the road surface when conditions are less than perfect. In general, the best way to improve tire road grip is to increase the amount of tire surface area (i.e., rubber) that comes into contact with the road. So, under ideal conditions (i.e., a perfectly flat, dry roadway), the best traction is provided by a “bald” flat-surface tire. (Think about the tires on a dragster.)
But, other than drag racers, who drives under ideal conditions? Think about it – just a quick drive to the grocery store will likely take you over a number of potholes, bumps, debris, oil from other vehicles, etc. And if you are driving on a winter day or in the rain, you may encounter minor flooding, ice, mud, and who knows what else? Drag racing is really nothing like “normal” driving, and those big, flat drag racing tires offer very little in the way of “winter tire performance.” In fact, throw a few bumps and some water onto a drag strip, and the next set of races will more likely resemble a “demolition derby” because flat-surface tires tend to hydroplane when they hit water.
That’s why the tires (or snow tires) on your family car or truck have deep treads cut into the surface. The channels between the tread blocks are there to disperse water from the roadway and prevent the tires from sliding.
In addition to dispersing water from the tire’s surface, the sharp edges on the tread blocks enable the tire to “grip” the road and improve tire braking. With siping, thousands of thin slits (called “sipes”) are cut into the tread blocks, thus providing more sharp edges, more tire surface on the road, more water dispersed, better ice traction and more “gripping power” for your tire.