Which tire is best, and when? Winter/snow tires vs summer tires.
Bridgestone Blizzak WS80 (Winter) - http://amzn.to/2hqRTgD
Bridgestone Potenza RE-71R (Summer) - http://amzn.to/2gXJX2Q
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Winter Tires: https://youtu.be/8OifbH5siF0
Winter tires are designed with a compound that remains flexible at low temperatures, while summer tires are designed to remain more firm, but will have a stickier compound at higher temperatures. An all-season tire is simply a compromise between the two. The major difference between the compounds comes down to something called the glass transition temperature. This is the temperature at which molecules in the rubber of the tire move less freely. In this low energy state, the molecules become more plastic-like, and this reduces the friction between the rubber and the road. For winter tires, the glass transition temperature is very low, where as for summer tires this transition range can be around 40-45 degrees F. Below this temperature, winter tires will perform better.
When the temperature of the tire increases above the glass transition temp, the molecules move more freely, the rubber becomes more pliable, and the tire will have more friction with the road, giving better traction. That said, as temperatures increase, there is a point at which the molecules begin to move too freely, and the rubber starts to become gummy, dramatically increasing wear, and changing the handling characteristics. Winter tires will wear very quickly at higher temperatures, where as summer tires will provide better grip, response, feedback, and handling.
This temperature range of the compound remains vitally important regardless of conditions. For example, if it’s raining, and it’s say, 70 degrees F outside, the summer tire will have a grippier compound at this temperature. Assuming you don’t have standing water, and the tire is touching the road, the summer tire will have more grip in the rain at this temperature.
So what are some of the other advantages of a summer tire? Well, this RE71R tire specifically was surprisingly inspired by motorcycles, developed from a high grip polymer Bridgestone used in MotoGP. The tread pattern has a wide center rib, which gives you a lot of response in steering and turn in, and it has massive shoulder blocks on the outside, unbroken, with no pass through grooves. The stiff shoulder blocks provide high grip and cornering, and for accelerating while going straight. You’ll also notice two large circumferential grooves with angled grooves and directional tread pattern for removing water.
Another interesting change on the RE71 is that it’s a little more rounded than the RE11, kind of like a motorcycle tire, and what Bridgestone has found is that this slightly increases the contact patch of the tire versus the RE11 during steering and turn-in, maximizing grip while cornering. The sidewalls are also stiffer than your average touring tires.
The winter tire, on the other hand, has significantly different design characteristics. Immediately you’ll notice a deeper tread. Deep tread allows for collecting snow, as snow on snow traction is actually pretty good. The trade-off, however, since the tread blocks stick out further, is that they’ll be less stiff. The stiff tread blocks of summer tires is what gives them a more responsive, precise feel. You’ll also notice siping, little zig zag grooves in the tread, which you won’t find on summer tires. This provides more bitting edges to grip the snow and ice, and is also another location to collect snow. Zig-zags help minimize the loss in stiffness, however the sipes will still result in more flexible tread blocks.
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