Controlling your truck’s weight transfer is the key to maintaining traction and steering
By Mark Cox
An overnight dusting of snow crunched under the tires as the driver of the 4×4 crew cab pickup rolled slowly through the suburban Idaho neighborhood and made a turn towards the main highway a few blocks down the hill. The light at the “T”-intersection flipped to red a half-block before the highway and the driver instinctively slipped his foot to the brake pedal and started braking.
A second later his brain realized there was a big problem: We aren’t stopping before the intersection.
A combination of too much speed and too little traction caused the ABS system to chatter away as the tires kept rolling.
A few seconds later the truck slid half sideways into the busy intersection as momentum and gravity did their thing.
Welcome to the realities of winter driving.
There’s no doubt any contractor or business owner who lives or works in the Snow Belt has had the unpleasant experience of losing vehicle control in the winter.
For some it may have been only a momentary happening and the skip of a few heartbeats.
For others, well, there was probably a lot of company paperwork to fill out and an insurance claim to file.
Most of us know the more slippery the road, the higher the speed, the heavier the vehicle, or a combination of all three means the longer it takes for steering, acceleration and braking inputs to affect the vehicle.
Driving on slippery surfaces requires you to make vehicle control inputs far earlier and much slower and smoother than you would driving on dry pavement.
It’s all related to controlling vehicle weight transfer.
BASIC DRIVING TIPS
As you drive down a level road at a constant speed, your truck’s weight is “neutral,” or balanced evenly front to back.
However, as soon as you begin to decelerate, that weight balance shifts forward. This puts more weight on the front tires, giving them more grip, helping both braking and steering.
At the same time the rear tires have less weight on them and, consequently, less traction.
Conversely, if you accelerate, more weight shifts to the rear tires, which gives them more grip – and the front tires less grip.
These driving inputs and weight shifts go unnoticed in good driving conditions.
But on snow and ice they are magnified a hundredfold because the tires are already at their limit of grip before any weight transfer begins.
In simple terms, when negotiating a turn on a low-grip surface like a snow-packed road, always slow down slowly in a straight line so you are utilizing your truck’s available grip at all four corners for deceleration.
Then begin to steer into the turn after you have finished decelerating and your foot is off the brake.
Doing so allows the vehicle’s weight transfer to provide braking to the front tires, and you gain steering effectiveness through the corner because you are using 100% of the grip to steer.
As you exit the turn and the front tires are once again pointed straight ahead, slowly accelerate, using the weight transfer to the rear tires for added grip.
Remember: Brake. Steer. Accelerate. But never overlap those driving inputs.
FOUR-WHEEL DRIVE ADVANTAGE
At this point, someone always makes the comment, “But my truck has four-wheel drive, so it’s okay to drive faster.”
Sorry to burst the 4×4 bubble: Four-wheel drive can never overcome the simple laws of physics and weight transfer.
-wheel drive does allow a slightly larger margin for weight-transfer error during acceleration, but it cannot magically create better braking or steering.
That’s where so many 4×4 owners make their biggest driving mistakes.
In fact, 4×4 trucks are more difficult to brake and steer than cars because they are heavier and usually run wider tires, which typically creates less traction on snow/ice.
More truck, more mass, more weight transfer mass, more difficult to control.
SMOOTHNESS IS KEY
The best winter drivers are the ones who are smooth.
The best winter drivers are the ones who are aware of what’s happening around and way in front of them.
If you decelerate or brake suddenly or harshly, weight transfer will occur in a corresponding manner. Decelerate or brake smoothly and progressively, weight transfer will follow suit.
Keeping vehicle control in winter driving conditions requires smooth, progressive transitions.
Drive like you have the proverbial raw eggs under your feet; light throttle, light brake, light steering inputs.
For example, if you slow down abruptly approaching a curve, the weight will abruptly shift to the front tires. Not good because on snow the front tires can grip, lose all grip, or a combination thereof while that abrupt weight transfer will unload the rear wheels.
The result is very likely to be a snap “over-steer” situation, where the rear of the truck suddenly swings out. (This effect can be further aggravated by limited-slip of locking rear differentials.) Now you are forced to control your truck with a quick correction.
If that correction is too much, too late or both, rebound over-steer will occur and the loss of control continues downhill so to speak.
PLAN AHEAD, WAY AHEAD
In addition to being a smooth driver, focusing far enough ahead so you can plan and make the needed braking and steering adjustments in time are key to safe winter driving.
If you do this, your vehicle’s weight transfer and speed adjustment will happen more slowly and thus be more precise and predictable.
Although the grip will still increase at the front wheels and decrease at the rear wheels under braking, it will happen in a lineal and predictable fashion, almost as if the weight transfer is occurring in slow motion.
Timing and controlling weight transfer are also critical when you exit a corner, especially on low grip surfaces.
One of the most common problems affecting weight transfer in cornering occurs when you accelerate too soon.
When the front tires are even close to their grip limit, the slightest amount of early acceleration will unload the front wheels and severely reduce your steering effectiveness. This is the dreaded “understeer.”
To get back steering control in an understeer situation, straighten the wheel (reduce the steering angle).
Turning sharper only makes the lack of steering worse.
So as the road ice up this winter, slow down, plan ahead, and be a smooth operator. It’ll pay big dividends.
ABOUT THE AUTHOR: Mark Cox is the director of The Center for Driving Sciences in Steamboat Springs, Co.., and a professional Rally driver. He’s also the lead instructor and head of the Bridgestone Winter Driving School; 800-WHY-SKID.