AUTOMOTIVE BEST BUYS


Thursday, June 24, 2010 — THE MEDICINE HAT NEWS


7


An all-season tire will have between 20 and 25 perc ent more gripping edges than a summer tire. A winter tire has about 40-50 per cent more than a summer tire.


An all-season tire has smaller tread blocks than a summer tire.


A high-performance all season tire has a mix of the attributes of a winter tire and summer tire, which ultimately means it’s a compromise. The winter tire will be better in the snow and slush and the summer tire will be bet- ter at cornering and will be more stable at high speeds.


Winter tires have raised tread and smaller tread blocks to help pad- dle away snow and slush. The tread is soft and not generally stable enough for high-speed driving. Note the small creases that grip the road surface but also destabilize the tread.


By JEFF MELNYCHUK WHEELBASE COMMUNICATIONS


T


his is where the rubber really meets the road.


Your old tires


are so worn that they’re practical-


ly transparent. But do you get summer tires and then swap them out for winter tires later on? Do you buy all-season tires and not worry about it? Or maybe a set of summer tires and then all-season tires for the winter because it doesn’t snow all that much where you are?


It’s really too bad that one


tire can’t do it all, because the simple fact is that the average all-season tire is a compro- mise that isn’t ideal in any condition.


Bill Vandewater knows. As


one of Bridgestone’s tire engi- neers, he talks about tread compound, gripping edges, siping and aspect ratio around the water cooler at work like the rest of us talk about last night’s game or the local news.


Keeping it simple, the basic


thing to know, according to Vandewater, is that summer and winter tires are specifi- cally built for those seasons, temperatures and driving surfaces. All-season tires, on the other hand, are a compro- mise between both since the properties of a good summer tire and a good winter tire contradict each other in near- ly every aspect, from tread design and softness of the compound (which used to be made of rubber but is now a blend of synthetic ingredi- ents) to sidewall construc- tion.


For the summer Since all-season tires are so


popular, the summer tire has evolved into the role of a high-performance tire built for speed and agility.


“A summer tire definitely


differs in the tread,” says Vandewater. “Big, blocky and larger is more stable than a tire with a small pattern.”


And in a high-performance


tire that needs to quickly and precisely react to what the driver is doing with the steer- ing wheel and the brakes, be- ing stable is everything. That also means a relatively shal- low tread depth that reduces the tire’s tendency to squirm


around and deflect when pushed closer to limit.


A summer tire also has a


short, stiff sidewall to aid steering response. That means a 30- or 40-series side- wall height, a number that in- dicates the percentage of the tire’s overall width.


“Sizing is a big issue since


there are no 60 or 70 series summer tires,” says Vandewater.


As well, outside shoulders


have larger tread blocks for cornering, while the inner ar- ea is built to channel water away to keep the tire from floating on top of the water, a condition know as aquaplan- ing.


For the winter In sharp contrast to the


summer tire, the winter is all about paddling slush and snow out of the way.


A different mission means


completely different qualities. A winter tire has deeper grooves and more of them, which means more gripping edges to help over slippery surfaces. They’re usually nar- rower, too.


“Wider tires have a tenden-


cy to float while narrower tires dig into the snow,” says Vandewater. By contrast, a wide summer tire puts more tread on the pavement, which is a good thing.


“Tread is designed to work


in a temperature range. Winter tires are designed to work in cold temperatures.”


A winter tire is soft to stay


pliable in the cold, which helps it grip. A summer tire hardens up in the cold and actually works against itself, unable to conform to surface irregularities.


“Running winter tires all


year around . . . (they’re) rela- tively soft, which makes them unstable.”


They also don’t last.


Driving snow tires in the summer is a sure way to kill them says Vandewater, since they’re so soft. They’ll wear down in no time flat, pardon the pun, rendering them inef- fective in deep snow.


“Your fuel economy also


takes a hit.” The deep grooves, about


30-50 per cent deeper than that of a summer tire, might help you get through the snow, but they also take away


from steering sharpness. As soon as the snow is


gone, change to your set of summer tires.


Increasing the traction in a


snow tire are sipes, which are tiny, nearly invisible slices in the tread that add more grip- ping edges. By contrast, a summer tire has no sipes, which helps to stabilize the tread to make it more respon- sive and better able to take the heat from high-perfor- mance use.


All-season dilemma Since summer tires are


generally reserved for high- performance vehicles, your only choice might be all-sea- son tires for summer driving. And while they’re a compro- mise between winter and summer tires, that doesn’t mean they’re bad.


They have a moderate


tread depth, somewhere be- tween summer and winter tires, more sipes and gripping edges than a summer tire and less than a winter tire. That makes an all-season less grip- py in both extremes.


The compound is designed


to work in a broad tempera- ture range, again a compro- mise.


Driving a vehicle that came


with summer tires from the factory in the winter means a change, but to what? Vandewater suggests winter tires if they’re available to fit your vehicle. Low-profile win- ter tires are harder to come by, but “we do make 40-series winter tires.”


If not, it might be possible


to buy different (smaller) rims and winter-specific tires with taller sidewalls, which will al- so help spare your shiny sum- mer wheels the grief of soak- ing in road salt.


Either way, you’ll need to


back off aggressive driving in recognition of the decreased traction.


“All-season is a compro-


mise but the most practical tire for most people.”


Jeff Melnychuk is Wheelbase Communications’ managing edi-


tor. He can be reached on the Web at: www.wheelbase.ws/mail- bag.html. Wheelbase Communications supplies automo- tive news and features to newspa- pers across North America.


Asymmetrical


This high-performance sum- mer tire has large tread blocks at the outer edge (right side) for cornering grip and wide grooves for shedding water. The design, called asymmetrical, allows normal rotation if all the tires are the same size. In a staggered arrangement where the front tires are smaller than the rears, the tires can be rotated left to right only.


Directional


A directional high-performance tire has to be mounted with the sidewall arrows pointing for- ward, which means the tires can only be rotated front to back and not side to side as is the case with an asymmetrical tire. If the tires are different sizes front and back, directional tires cannot be rotated — at all — unless they’re removed from the rims. Characteristic of most directional tires is a swooping centre section show here.


This 335-30/20 tire has 13.2 inches of section width (335 millime- tres converted to inches). The sidewall height is 30 per cent of the section width, which is four inches. The tire height is therefore 28 inches (the 20-inch rim diameter plus two times the sidewall height).


What’s your direction?


Buying directional tires — designed with a preferred for- ward rolling direction — used to be the norm for high-per- formance summer tires, but new designs mean easier side-to-side and front-rear rotation.


Here’s a dilemma. Summer tires for the factory wheels on this car are no problem, but there are literally no winter tires available in 275-35/18. There are also no smaller-diameter steel wheels, which could be fitted with winter tires, that will fit over the brake cali- pers. The only choice is an all-season tire (in limited brands and tread designs), which might mean that this rear-drive car could be relatively useless on snowy days.


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