Every morning now, the driving gets a little lumpier, as those all-season tires work out the flat spots on their bottoms from parking overnight.
That thump, thump, thump is a message. The all-season rubber on your car is just not happy trying to flex any muscle to grip the pavement as temperatures drop.
Those are the signs that tell you now is the time to change over your tires to winter rubber.
Tire grip fades as temperatures drop; that is one of the basic laws of driving. However, there is an amendment to that law, winter tires increase grip as the mercury plunges. That amendment to the law kicks in at about 7 C above zero. As all-season tires’ rubber hardens and grip drops, winter tires stay soft and increase their gripping qualities. The colder it gets the happier and grippier they get.
Once upon a time snow tires were just that, snow tires. The plan was always line up at the local garage for the changeover when the weather forecaster frowned and said those ominous words, “snow clouds on the horizon.” Now technology has morphed snow tires into winter tires. These winter tires show performance improvements over high performance and all-season tires on dry clean pavement even at slightly above zero temperatures.
Many readers in the GTA think that because our major streets are plowed clear of snow, they can drive on their all-season tires. These one-tire drivers are happy in their belief that they will not get stuck. That is true, but what they forget is that driving also consists of braking and turning. Braking and turning can get a driver around a stopped problem and for that, we need grip.
Last winter the Star Wheels section did a few tests to check if winter tires really were better at dealing with life’s on-road emergencies when the temperatures were low and the pavement bare. Canadian Tire Corporation was eager to help and supplied three sets of tires for evaluation; their own Goodyear Nordic winter tire, a Goodyear Allegra all-season tire and a high performance tire, the new generation Goodyear Eagle GT. It turned out the Eagle was also classed as an all-season but its performance heavily skewed for summer grip.
Mosport was kind enough to provide their skid pad and Jack Benzacar of tirebutler.com provided one of his trucks and tire changing crew. We ran the tests twice to see what the different winter temperatures did to the results. Fellow driving instructors Gerry Low and Rick Morelli helped pilot my trusty Jetta through the tests.
In February at -12 to -14 C and heavily overcast, the skid pad numbers showed the Nordic was a clear winner at .433 G, the all-season Allegra came in at .397 G of grip while the big fat Eagle GT managed .370 G. I mention the width because while all the tires were nominally the same size, the Eagle was built wider to maximize its summer grip. That extra width probably gave it an unfair advantage in all our tests.
In March when the thermometer hovered around a balmy -6 C and the sun was shining the grip improved dramatically. The Nordic produced .727 G, the Allegra came close at .700 but the Eagle GT still trailed at .601 G. The warmer and sunnier day improved all the tires’ grip but still not up to summer standards. I would expect the Eagle GT to produce summer numbers above .86 G.
Emergency braking to me is what really matters when things go sideways in front of me. In February, with the temperature at -14 C and no sun on the pavement, panic stops from 80 km/h produced stopping distances of 49 metres for the summer Eagle GT, 39 metres for the Allegra all-season, and just 34 metres for the CTC/Goodyear Nordic Winter tire.
When the sunny skies of March heated the pavement and the air temperature was -6 C, we tried the same panic stops. The Eagle GT improved to a stunning 27.3 metres. That just shows how much some sun can affect tire performance. The Allegra stopped in 19.3 metres but the Nordic Winter still beat that at 16.6 metres.
To consider how well these tires can take evasive action on winter tarmac, we set up a simple slalom with cones placed 10 steps apart and a very sharp left turn at the end. Again the Nordic Winter set the pace with a time of 21.3 seconds in February when it was cloudy and 14 below. The all-season Allegra came next at 22.1 seconds and the summer sports tire clocked in at 24.6 seconds.
In March with the sun out and air temperatures of just -2.5 C, the Nordic tripped the timer at 16.2 seconds for the same slalom. The all-season came in at 16.63 seconds and the summer Eagle managed 18.02 seconds.
The finishing order was much closer but the order prevailed; winter tire, all-season tire and then the summer tire. The big surprise was the decrease in the times by each tire when sunshine had heated the pavement from dawn until about 11:30 a.m. when we ran the slalom test.
Stopping distance spreads of 15 metres at -14 C can create a huge safety buffer for any driver, just by switching tires for the winter. Even at -6 C, the spread was 10.7 metres better for the winter versus the summer tire. Isn’t it time to switch over now?
Originally published in the Toronto Star.
