Driving in winter, like walking in winter, is all about traction. And traction can be a particular challenge in pickup trucks.
In a four-wheel-drive pickup, with 4WD engaged, all four tires can share the driving task – effectively doubling the tractive force available for acceleration. But two-wheel-drive units are at a distinct disadvantage.
A passenger vehicle typically has 55-60% of its weight on the front wheels and 40-45% on the rears. But pickup trucks are designed to carry loads. So as little as 30-35% of the vehicle’s weight is on the rear wheels when it's empty, to allow for the addition of a load in the rear.
Therein lies a problem, for both two and four-wheel-drive pickups, but especially those with only the rear wheels being driven.
In a typical vehicle, as it accelerates, about 5-10% of the total vehicle weight is transferred to the rear wheels through the simple laws of physics. The amount transferred depends on several factors, not the least of which is available traction.
As more weight is transferred, more traction is created at the rear tires. Traction is a direct function of the load (weight) acting on the tires.
In a pickup, the lightly-laden rear wheels typically can't provide enough grip on slippery surfaces to create much weight transfer. If the rear tires spin when you start to accelerate, there will be no transfer and not much acceleration! It's a Catch 22.
There are two ways to address this issue – tires and weight.
The tires that come with a truck from the factory and those commonly purchased as replacements are typically 'all-season' tires – even if they have a visibly aggressive tread design. Which means, they're really only three season tires.
Their tread and its contact patch – the palm-sized patch of rubber actually in contact with the ground - are designed to cope with extremely high temperatures in summer or when carrying lots of weight. But that tread becomes rock hard as the thermometer dips near and below the freezing point. Grip is minimal and worsens as temperatures drop further.
That aggressive looking tread? In many cases, it's marketing folly, more for looks than anything else. The tire may be good in soft sand, in hot weather, but at the same time it puts less actual tread or rubber on the road, reducing the ability to stop or turn suddenly. That same tread, while looking rugged, hardens in cold conditions, becoming even more useless.
If you want to improve winter grip, buy proper winter tires and put them on all four wheels. A quality winter tire, wearing the 'snowflake within a mountain' symbol has a chemical composition designed to retain its grip at temperatures when summer or all-season tires become nothing more than skis.
This new generation of “winter” tires has been developed to not only put more actual tread on the ground – and icy surfaces, but to cut through snow while remaining supple as the thermometer drops retaining maximum grip.
The second thing you can do to improve traction with your two-wheel-drive pickup is place some additional weight over the rear wheels. The whole idea behind a pickup truck's architecture is to carry a load back there.
But too much can be as bad as too little.
Putting weight in the box will help traction, putting but too much will create a new problem – a tendency to spin out of control as that heavy rear end tends to swing out in the turns.
How much weight to add? There is no definitive answer but a good rule of thumb is to defer to the manufacturer’s expertise and in-house testing.
Look in the owner's manual under "standard" and "maximum" vehicle payloads. This is the safe range of weight that will keep you within the ride and handling characteristics the engineers developed for your specific vehicle.
You can greatly improve traction in winter with weights well below the maximum payload rating – 50-to-100 kilos will do wonders. Something that results in a front/rear weight distribution similar to a passenger car is probably not a bad choice.
Sandbags work well and should be placed at the rear of the bed for maximum effect and secured to prevent them from sliding around under braking or in a crash. Whatever load is used, it needs to be secured.
Keep in mind that adding weight will cost you at the pumps as the engine has to lug it around all winter. Plus, by increasing the total weight of the vehicle you will increase stopping distances.
In either two or four-wheel-drive pickups, when you apply the brakes the heavily loaded front tires, have plenty of grip and weight will shift off the rear wheels and unto the fronts creating an even greater imbalance. If you attempt to turn while braking, those lightly loaded rear wheels won’t have much grip, and will slide very easily. Do your braking in a straight line, easing off before starting to move the steering wheel for a turn.
Those with four-wheel-drive pickups should also remember that the additional driving wheels are only helpful when accelerating. They do nothing to improve stopping or turning.