Results of Winter Tire Testing on a Multi-Function Activity Vehicle

Transport Canada has conducted tire testing on a Multi-Function Activity Vehicle (MFAV), often called a minibus. The purpose of the tests was to identify the safest configuration of tires on MFAVs for winter highway driving.

The MFAV’s performance was tested on snow while fitted with four winter tires in the back and two all-season tires in the front, and then re-tested with winter tires on all wheel positions. These two scenarios show differences in braking distance required, cornering and basic handling.

While each province regulates tire usage, Transport Canada maintains its position on the safety advantages of winter tires, designated with the mountain snowflake symbol, on all wheel positions during the winter season.

DEFINITIONS

Understeer: happens when the front tires lose traction before the rear tires and the vehicle plows straight ahead rather than in the direction the wheels are pointing. Understeer is considered a stable condition because vehicle control can be regained by slowing down or reducing steering input.

Oversteer: happens when the rear tires lose traction before the front tires and the vehicle begins to rotate sideways about its centre of gravity or spins out. Oversteer is considered an unstable condition because, in general, vehicle control cannot be regained.

VIDEOS OF TESTS

BRAKING TEST

Minibus Equipped with 2 All-Season & 4 Winter Tires

Minibus Equipped with 6 Winter Tires

These video clips show a braking test of a 21-passenger minibus on a snow-covered surface. In this test, the minibus is accelerated to a speed of 80 km/h and then the brakes are fully applied in order to bring the bus to a full stop in the shortest distance possible.

The minibus is equipped with different tires in different tests:

  • White wheels on the front: two all-season tires on the front axle and four winter tires on the rear axle.
  • Grey wheels on the front: winter tires on all six wheels.

When fitted with six winter tires, the minibus stopped an average of 5.6 meters shorter when compared with the stopping distance with two all-season tires on the front and four winter tires on the rear.

The vehicle stopped straight and stability was maintained in both stopping test configurations.

STEADY STATE CORNERING TEST

Minibus Equipped with 2 All-Season & 4 Winter Tires

Minibus Equipped with 6 Winter Tires

These video clips show the same 21-passenger minibuses being driven around in a circle with a radius of 62 meters on a snow-covered surface. In this test, the vehicle is gradually driven up to a speed where it is no longer able to follow the diameter of the circle. One of two things could happen:

  • Either the minibus begins to run in a larger diameter circle, a condition called "understeer";
  • or the vehicle spins out by losing traction at the rear, which is a condition known as "oversteer".

In this test, the minibus attained an average speed of 40.6 km/h with winter tires in all six wheels positions, and an average speed of 36.3 km/h when the two all-season tires were fitted at the front.

The vehicle was stable and exhibited a moderate to pronounced understeer condition in both steady state cornering tests. It should also be noted that the minibus could not be made to oversteer by rapidly applying and releasing the accelerator pedal while the vehicle was in a constant radius turn.

HIGH SPEED SLALOM TEST

Minibus Equipped with 2 All-Season & 4 Winter Tires

Minibus Equipped with 6 Winter Tires

In these videos, the minibus is subjected to a series of consecutive left and right turns at a speed of 80 km/h between a series of cones placed in a straight line with a distance of 60 meters between them, on a snow-covered surface.

Unlike the steady state cornering test where the bus is operated in a fixed turn radius in one direction, the slalom test determines the dynamic steering characteristics of the minibus by rapidly turning one way, then the other.

As can be seen in the test above, the minibus, when fitted with the two all-season tires on the front axle, could not follow the prescribed path and hit the second set of cones. The minibus was able to follow the prescribed path when fitted with winter tires on all six wheels.

The vehicle was stable during all aspects of the high-speed slalom test and exhibited moderate to pronounced understeer.

LOW SPEED SLALOM TEST

Minibus Equipped with 2 All-Season & 4 Winter Tires

Minibus Equipped with 6 Winter Tires

In the video shown above, the minibus is subjected to a series of consecutive left and right turns at a speed of 40 km/h between a series of cones placed in a straight line with a distance of 30 meters between them, on a snow-covered surface.

Again, unlike the steady state cornering test where the minibus is operated in a fixed turn radius in one direction, the slalom test determines the dynamic steering characteristics of the minibus by rapidly turning one way and then the other.

As can be seen in the low speed slalom test video, the minibus, when fitted with the two all-season tires on the front axle turns with pronounced understeer. This can be observed in the additional steering angle and resulting spray of snow coming from the front tires.

The vehicle was stable during all portions of the low speed slalom test and exhibited moderate to pronounced understeer.

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