Winter Driving: The Pendulum Effect

Winter Driving: The Pendulum Effect
No matter how capable the SUV, it still needs winter tires. (Photo: FCA)

Whoever told your customers that SUVs don’t need winter tires, was lying.

The dictionary defines the Pendulum Effect as follows: “Also called pendulum law; Physics; a law, discovered by Galileo in 1602, that describes the regular, swinging motion of a pendulum by the action of gravity and acquired momentum.

What does this have to do with tires? Well, consider the market today: SUVs and CUVs are overtaking cars in popularity (for ease, in this article, we will refer to both types as SUVs). Also, while the focus is on SUVs, many of the pendulum effect points raised here apply to minivans, pick-ups and cargo vans.

People buy SUVs for various reasons, but a key reason is “perceived safety,” which is based on a higher seating position, the assumption of greater vehicle weight and mass being safer in the event of a collision, and, in some cases, All Wheel Drive (AWD).

Why do I say “perceived safety?” Well, the higher seating position only gives you a sightline advantage if you are the only SUV on the road. If you are making a left turn and the opposing vehicle is also an SUV or Minivan, then you do not have a sightline advantage. That higher seating position means the vehicle has a higher centre of gravity since all the heavy parts of the vehicle, the engine, the transmission, the differential, the passengers and the cargo are higher off the ground. The greater vehicle weight and mass, at the higher centre of gravity, create a pendulum effect reducing the balance of the vehicle during cornering, or collision-avoidance maneuvers, or hard braking.

The trouble with AWD

AWD is reliant on the traction provided by the tires, and AWD does not help with braking. In fact, as an AWD vehicle has more parts it tends to be heavier and in turn that weight at the higher centre of gravity further increases the pendulum effect, thus resulting in longer stopping distances.

To keep the price point low, many automobile manufacturers offer SUVs with Front Wheel Drive (FWD) only. In such cases, the SUV is just a FWD car, with extra weight and a high centre of gravity.

The message here is that SUVs need winter tires. Nothing can compensate for poor traction at the contact patch. Remember the basic truth—the tire is the only part of the vehicle that touches the road.

The high centre of gravity coupled with the extra weight of an SUV can be dangerous in the winter. The load transfer to the front tires under hard braking, the unloading of the rear tires under hard braking (thus reducing their contact patch), the load transfer to the outer tires in a corner or collision avoidance maneuver—all create the conditions for a skid. This is the pendulum effect, and once the pendulum starts to swing in the wrong direction, it is very difficult to stop the swing.

Education vs. myths

As we get into winter, please educate your customers and dispel the myth that SUVs do not need winter tires, and the myth that AWD solves all winter driving issues. Without winter tires, the SUV is more dangerous in winter than a car.

They bought that SUV to be safe. They bought that SUV because they need to transport their family and to carry stuff. They have spent a lot of money on that SUV. Encourage them to make the relatively small investment in winter tires to truly make that SUV a safe winter vehicle.

Thinking rationally, what is the value of safety?

Share it !