With winter tires, it’s all about the grip
QUESTION: Last week somebody was asking about studded tires, and you wrote how you feel ice tires are superior. I was wondering if all winter tires are ice tires and if not, how can you tell the difference? Answer: Great question. The Canadian Rubber Association says “tires displaying the mountain snowflake symbol meet or exceed industry-established snow traction performance requirements and have been designed specifically for use in cold weather and severe weather conditions.” These are classified as “winter” tires, with a mountain symbol (which looks like a jagged triangle) on the sidewall of the tire and a snowflake inside it. However, not all “winter” tires are created equal. Some are better on icy roads than others. Grip on ice is derived by two methods. The first is achieved by the rubber compound itself. If the rubber remains more flexible as temperatures drop, then it can conform to the icy road surface and provide better grip. Often, special additives are included in the rubber compound, including things such as walnut-shell particles, to help with the grip. The second method of gripping icy roads is the mechanical design of the tread. When you put pressure on ice, a thin layer of water forms on the surface and makes it even more slippery. Anyone who curls knows this principle well — sweep hard and the rocks travel faster and further. Part of the tread’s mechanical design is to provide voids in the tread surface so the water can be displaced from the surface and held in the tread until the tread is no longer in contact with the ground. This allows the rubber to get better contact with the ice and more traction. The other mechanical method used is to build thousands of sipes (fine cuts) into the tread surface. The edges of each sipe cut can grip for better traction. Generally speaking, tires with more sipes on them will work better on ice, but there are more factors involved than just the number of sipes. The tire manufacturer’s description of the tire will indicate if it is better suited for ice traction than other winter tires of the same brand, so this is the best way to pick the best “ice” traction tire from a particular brand. Also, don’t confuse some of the latest “fourseason tires” with winter tires. Four-season tires may be better in cold weather than allseason tires, but they are still not as good as winter tires. Question: I have a 2008 Chevrolet Silverado 4x4 truck, and in the latest cold snap, it wouldn’t go into gear. The engine started fine, but a warning message came up on the instrument cluster to “Service the 4x4 system.” Everything seems OK, but if I put the transmission in gear, the vehicle doesn’t move. It has an automatic transfer case, and the small indicator light on the control is flashing. Is this a problem with the transmission or has something in the 4x4 system failed? Answer: The problem is in the transfer case controls, and there is likely nothing wrong with the transmission. The transfer case uses an electric motor and gear pack assembly on the side of the transfer case to switch between two-wheel drive, 4-high and 4-low ranges. In automatic mode, it is automatically shifting between two-wheel drive and 4-high mode based on the amount of speed difference in the front and rear driveshafts, which represent tire slip. There is also a “Neutral” mode in the transfer case, and I think your transfer case is stuck in this neutral mode. Neutral mode is required to allow the transfer case to be able to shift between 4-high and 4-low modes. It can also be used when the vehicle needs to be towed with the tires on the ground. The electric motor on the transfer case (GM calls it the encoder motor) likely needs to be replaced. Before doing that, check the wiring to the transfer case encoder motor for damage from mud or ice. If the wiring looks good, remove the encoder motor assembly. The transfer case can be manually shifted into gear with a wrench when the encoder motor is removed, so you should be able to drive the truck to a repair shop if necessary.