Snow tires
Dr. Selim Erhan | TLT From the Editor March 2022
If the science isn’t enough to sell you on their merits, driving in wintry conditions may prove their worth.
I recently came back to Chicago in the middle of a snowstorm. As the plane was landing on a completely white runway, it was hard not to imagine what might happen if we started sliding, going sideways or were not able to stop, but luckily none of these happened! We were very thankful. This made me think of some old experiences and to write about snow tires.
Some people, especially ones that have driven with snow tires, love them. Others think they are not that necessary. Especially with SUVs and traction control, some of the risk is mitigated. It also is an additional expense—although it prolongs the life of both the winter and summer or all-season tires, so the expense disappears in the long run. Another downside is that extra storage space is required, and they must be switched twice a year, which is additional time and money. Of course, these calculations are fine when one sits at the kitchen table. It is an entirely different situation when one starts sliding toward oncoming cars!
I lived on the West coast of Michigan during my college years. The 40-mile-wide stretch is a snow belt, and one gets a variety of snow, blizzards, blowing snow and whiteouts. I remember times when I slid into traffic, did doughnuts merging into a highway and a few other unpleasant events that I am sure many are familiar with. There were not many options in those days, and dealing with snow and ice was part of life.
In recent years, I have been involved in tire research and the use of vegetable oils, especially in winter tires. Vegetable oils with very low-glass transition points make excellent process oils for winter tires. Tire structure actually is very complicated. On the physical side, there are different layers of materials such as cloth, steel belts and many layers of different elastomer formulations that one would not think looking from the outside. The real complication, though, is in the chemistry of the elastomers and additives. Natural or synthetic elastomers are made of polymer chains that are not connected. So when they get warm, the chains start moving and separating like spaghetti strands.
To give the product strength and elasticity, what we generically call rubber, these strands are crosslinked. To achieve this, the elastomers are compounded with cross-linking agents, accelerators, polymerization retarders and other additives such as silica or carbon black that will strengthen the rubber to achieve a desired level of performance. But there is a very delicate balance in this performance. The tire must grip the road but not too much, known as rolling resistance. A lower rolling resistance is required to move the car with less energy, thus reducing fuel consumption. The tire must have good performance on dry pavements but also on wet pavements, snowy pavements and icy pavements, all needing different rubber formulations and tread patterns for optimum performance.
The tear resistance of the tire, oxidative stability, wear characteristics and road noise must be dealt with, especially in the tread design. A design that gives good grip on snow may become too noisy on dry pavement. In fact, the manufacturers put wet traction, rolling resistance and abrasion resistance at the corners of what they call a “magic triangle.” Usually as one property is improved, another suffers. Once a reasonable balance is reached, the tire will work well at that particular temperature but will have a different performance with significant temperature changes. Today, tire manufacturers can make good summer tires that will not soften at high temperatures and will provide a good grip, low fuel consumption and a long life. They also can make good winter and snow tires where the polymers are softer at low temperatures to give a good grip and will have the desired performances below 50 F. But a summer tire will get too hard in winter, and a winter tire will get too soft in summer for safe or economic use. An alternative to changing tires is to use “all-weather” tires that are hybrid tires that perform reasonably well in non-extreme temperature conditions.
The science makes sense, but it is still hard to imagine how it feels or performs until one drives on them. I found out the value of snow tires with an unplanned situation some time before I learned about the science of tires. It was November, and I was driving back to Chicago with my daughter. A snowstorm was expected later in the day. We were in a rear-wheel-drive car with not-so-new tires, which I had been planning to change before winter. Halfway through to Chicago, we ran into the snowstorm. It had started early. For the next two hours, my driving experience was a pure nightmare. Having my daughter in the car compounded my anxiety. Miraculously, we made it home without an accident, and that evening the first thing I did was start shopping for snow tires. The next day I had snow tires on my car. All the financial calculations, inconveniences and my previous snow driving skills had become insignificant. The very nasty driving experience had justified the decision many times over. The difference in the grip on snow and ice was like night and day. The safety factor is well worth the price.
Dr. Selim Erhan is director of business development for Process Oils Inc. in Trout Valley, Ill. You can reach him at serhan@processoilsinc.com.