What is a siping cut?
Siping was patented for tire application in 1923 under the name of John F. Sipe*. There are two common versions of the stories of this invention’s creation. One involving Sipe working in a slaughterhouse and the other as a dock worker. Both involve slick floors and Sipe getting tired of slipping on them. Then finding out that cutting slits in the tread on the bottoms of his shoes provided better traction than uncut tread. If you think of the soles of deck shoes you’ll get the idea. But Sipe thought about tires, and it wasn’t very popular.
At first it was only applied to solid tires and solid tires have a relatively small contact patch. That limited the siping cut’s effectiveness. It first became popular in the United States in 1939 when the Inventor’s son, Harry E. Sipe, applied this technology to the new low-pressure balloon tires.
Okay. So how does it work? A little bit about the water between you and the road first.
The mechanics of a water film and tire interaction can be broken up into three zones on the tire’s contact patch. The leading edge zone, zone one, is a water wedge boundary caused by displacement inertia of the water film. Zone two is a mixed zone of the water wedge boundary and a water squeeze-film layer. Zone three is dominated by the squeeze-film layer. The size of these zones can vary in length depending on speed. At very high speeds zone one will cover the entire contact patch. Hydroplaning. As speed decreases you can have partial hydroplaning where part of the tire load is supported by the water wedge. At low speeds zone three will cover the entire contact patch. While zone one and two can be removed by reducing speed the amount of time it takes for a tire to squeeze through the water layer in zone three is independent of speed and depends entirely on the physical properties of the tire’s contact patch and the road’s surface.
Zone one to three progress from left to right. Each zone of the tire and water interaction is clearly visible.
So basically. The tire is squeezing out the water between it and the pavement and, if the vehicle is going fast enough, some of it gets pushed forward back in front of the tire only to be rolled over again. Building up a wedge that can lift part or all of the tire off the pavement, If it doesn’t get pushed out to the sides or forward it gets squeezed under the tire. This last bit is the squeeze-film layer. Regardless of how fast or slow you are going the water in this zone gets squeezed out at the same rate.
Channels and groves in the tire tread can address the tire’s efficiency in dispersing the water wedge formed. Rain sipe patterns address the squeeze-film layer by removing the water from between the contact patch and road surface. As the tire deforms to the road surface the sipes expand and form a vacuum. This pulls almost all of the remaining water film into the siping cuts allowing better contact.
A little side note here. Snow tires and snow sipes act differently. Most snow tires will use a tight zigzagging pattern for the siping cut with multiple cuts running in parallel and the tire material is designed to remain soft in cold temperatures. As the tire deforms under the vehicle’s weight and movement forces, these sipes expose the jagged edges and sides of the cuts greatly increasing the tread’s surface area and allow for better keying to the road’s surface.
Okay. So aftermarket siping. Should you? Depending on the tire most tire manufactures would probably say “no” to altering the computer-designed siping and tread patterns. The manufacturing process has gotten a lot more sophisticated and precise. Locking sipes that allow the tread block to flex in only specific ways and pumping sipes that are specifically designed with internal gaps to hold more water. Adding additional siping cuts can destroy this pattern and actually do more harm than good. If testing showed that adding more siping cuts would help they would add them.
* Pat number: US1452099A. Filed: Nov 2, 1920. Published: Apr 17, 1923.
Header photo courtesy of BFGoodrich