Why don’t summer tires work in the cold? Does their effectiveness decrease with temperature in a linear or step like way?
In: Physics
Imagine summer tires as popsicles. When it gets cold, popsicles become hard and not so tasty. Similarly, summer tires are designed for warm weather and become less flexible in the cold. This makes them harder and less grippy on cold roads, like trying to use a frozen popsicle stick on ice – it just doesn’t work well. Their effectiveness decreases, and it’s not a smooth change; it’s like going from running fast to walking slowly when it gets cold.
Winter tires stay soft and rubbery when it gets cold. Summer tires become hard like hockey pucks because they are made to work well and be sticky in warm weather, but that performance due to being nice and soft in ideal warm weather comes at a cost of hardening up when it’s below 50 degrees.
The rubber formulas are different for different season tires. Summer tires are tolerant of the heat and won’t melt on hot asphalt or reduce your fuel economy too much by getting soft and increasing traction in warm weather. On the flip side, when they are really cold they will be hard instead of flexible, meaning less surface area touching the ground and less grip, so you are more likely to lose traction and slide or spin out in low temperatures.
In addition to what other people have said – the tread of tires is cut differently depending on what the expected conditions are. Summer (ie warm and dry) tires have large flat sections of tread that have large contact patches with the asphalt. This works great for dry asphalt, it is poor for water and ice.
Snow tires have likes of cuts (siping) that is designed so the treads will “cut” through the snow or water to gain better traction on the surface.
An analogy: If you have a large 4×8 sheet of wood, it will stick to a flat concrete floor really well, but if there is any oil or water on the floor the entire sheet slips, this is a summer tire. A winter tire has a lot of nails nailed through it, so it slides on a flat concrete floor more easily, but if there is water or oil on the floor, the nails cut through the water or oil and dig into the concrete. This is a not a perfect analogy, but it gets the point across.
As has been pointed out different compounds behave differently in different temperatures. All seasons start to lose effectiveness at about 7 degrees celsius.
When you compare that to a proper “summer” tire, you’re talking about a tire optimized for an even higher temperature range. At the extreme end of this, you can find high performance summer tires that warn you against using them below zero degrees, because the rubber will freeze and crack, destroying the tire. Michelin Pilot Super Sports and Michelin Pilot Sport 4S are the two I know off the top of my head.
I got housebound last year because I lived in a generally warm climate that got hit with a serious winter blast. My BMW on PS4S was my only car and it was not able to leave the garage.
The rubber has a mix that is meant to be working at a certain temperature range. Above and below, it won’t work the same way.
In your scenario, below recommended summer temperatures, it loses flexibility and so it doesn’t react properly at road asperities and generally has less grip (not being able to flex and enlarge the touch surface with the ground)
It’s not stepped, it may not be linear either. It’s probably a curve (but close to linear).
It happens for two reasons:
1. The rubber gets harder, meaning it can’t conform to the road as well. That means there’s less surface contact, and therefore less friction.
2. The tread is not designed to displace snow very well. Snow can be deep, while water on a flat road won’t be. If you can’t displace the lubricant (yes, water and snow are lubricants), you don’t have any road contact, and friction is radically reduced.
tires designed specifically for warm weather don’t have tread pattern’s designed to handle snow and ice conditions. Simple.
Do you know what a hockey puck is? Have you seen how effortlessly a hockey puck slides across the ice? It’s like that.
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