The are often required for 18 wheelers (and I am sure still are) when I was going over Snoqualmie Pass from Eastern Washington to Seattle as a kid and often required for cars as well. I remember having the police stops and having to help my stepdad put them on.
They provide immense traction in snow/ice that is compacted as others mentioned above, metal chains on your rubber tires.
They are especially important for rear wheel drive cars as back in “the day” they were quite common as most the weight is forward, with no traction to the rear drive wheel.
Without them, accidents are waiting to happen, or you would slide off the road, or spin and go nowhere.
Latest Answers