Under-inflating tires to improve traction has been the mantra of many instructors for decades: this is not always the case.
When I was learning to drive, my teacher instructed us that in certain conditions, it is better to let some air out of your tires to improve traction.
The idea was that by letting a little air out, the tires would sag, allowing more of the tire to come in contact with the road and creating more grip on slippery surfaces. There was probably more to that lesson that I don’t remember, but the lesson always stuck with me.
I never tried it, probably because the times I have found myself in snow and mud, I didn’t want to get out do it. A couple years ago, a good friend of mine and I were getting ready to go on a little road trip in the winter. It was a clear and sunny day, biting cold, but no weather in the forecast to be concerned about.
It had snowed a few days earlier, but the plows had been working day and night, and the road report was not bad, some areas of patchy ice, but nothing serious. Just before we left, my friend went around and let ten or fifteen pounds of air out of each tire, just enough to get the sidewall to sag some. I was reminded of the lesson my driving instructor had taught all those years ago.
“Why would you let air out?” I asked, knowing our trip was not going to take us into the wilderness. He explained that letting a little air out helps the tire be more flexible, so it is less likely to slide. “I have done this every winter now, for all these years,” he said. “If it wasn’t safe, I think I would have had a problem by now.” I just shook my head, said something along the lines of “Alright, it’s your truck, not mine,” or something like that, and we set off on our trip.
The trip went great, no problems with the tires or the roads, but the conversation bothered me. Why would reducing tire pressure help with traction? How could letting air out help tires to stop and corner in snow and ice? When I got home, I decided to find out for myself what the truth is according to the experts.
Save Some Gas and Drive Safer
The National Highway Transportation Safety Administration (NHTSA) reports that car accidents due to tire problems resulted in more than 700 deaths in 2017. They also state that only about 1 in 5 Americans properly inflate their tires. Under-inflated tires can lead to blowouts, which when experienced at high speeds, can result in highly unpredictable experiences. The NHTSA points out that under inflated tires reduce fuel efficiency, the farther from properly inflated, the more fuel wasted. NHTSA estimates that under-inflated tires can waste $0.11 per mile. For the average Philadelphia driver, that’s a savings of $1,367.85 every year based on data produced by the U.S. Department of Transportation, Federal Highway Administration (FHWA). So, properly inflated tires are safer and save gas.
But that is under normal driving conditions with dry roads and average temperatures. What about snow and ice, mud and rain and all the other adverse conditions in Pennsylvania? In an article for The Weather Network and Autofile.ca, Anant Gandhi, product manager for Bridgestone Americas said that tires should never be under-inflated in snowy and icy conditions. “"Deflating your tires simply doesn't work in this situation. In fact, you could end up damaging your tires if you drive on them under-inflated," Gandhi said. The reason for this is physics.
Different Tires for Different Driving Conditions
When you drive on icy and snowy roads with under-inflated tires, you actually lose grip because the wider, flatter tire surface loses shape and allows ice and snow to build up under the tires contact patch. In fact, TireRack.com, a leading online tire seller that also uses a private race track to test tires for consumer review, states that several vehicle and tire manufacturers recommend an increase in tire pressure of three to five pounds per square inch (PSI) when using winter tires or driving in adverse winter weather on all-season or mud and snow tires. You should not be driving in the snow on summer tires.
There are several reasons to increase tire pressure in winter. Winter tires are designed to have more flexible rubber in cold weather and more aggressive tread shape. Properly inflating winter tires allows the built-in functions to preform as intended, increasing traction in snow and ice and helping to accelerate and stop safely. Tires have a maximum pressure rating that can be found on the sidewall of the tire. The tire pressure is intended to be measured when the air in the tire is the same temperature as the air. When you drive on a tire, the friction warms the air and allows it to expand, increasing the pressure slightly.
Inflate your Tires Properly and Stay Safe
A tire that is properly inflated for mild or warm weather will be under-inflated in cold weather. Because of the low temperatures, the warming of air in the tire while driving is substantially less, which results in less of an increase in tire pressure while driving. Goodyear Tire Company reports that today’s tires can lose one or two psi per 10 degree air temperature change. So a tire that is properly inflated on a warm, 87 degree day in July will be six to twelve psi below proper inflation on those freezing, 26 degree January nights when the snow is piling up and ice forms on bridges and roads.
Tire pressure should be checked regularly. Many tire manufacturers recommend checking tires for damage such as nails, gashes or separated tread and checking pressure at least once a month. Most gas stations will have an air station that you can check your tire pressure and add air. If you are unsure how to check your tires, many service stations will be happy to show you the steps to safely check your tires.