What is roll in driving?

In this article we go into what body lean is and how it is an important consideration when looking for your next car to lease or purchase.

Just about every car has shock absorbers and springs attached to each wheel. This allows the body to move independently of the chassis beneath it.

Assuming you are driving at legal speeds, your car’s tyres will remain in contact with the road and the lean you experience is the suspension system expanding and compressing as the weight of the car shifts during cornering.

To get a quick, practical demonstration of body roll, drive down a road with a few sharp corners. The way your car leans to one side during cornering is called body roll. If you turn left, the car will roll to the right and vice versa.

Body roll occurs when a centrifugal force acts on a car as it goes around a corner. This force is the same thing that pushes water to the bottom of a bucket as you swing it around and sticks your clothes to the sides of a spinning washing machine.

Higher cornering speeds will result in a higher centrifugal force, causing more body lean. The suspension setup, weight, size and height of a car all play a part in how much body roll you will experience.

Not inherently. Body roll is a function of a car’s suspension system. Each manufacturer builds an element of body roll into their vehicles that most closely matches the driving characteristics they desire. There was a time, many moons ago, when body roll could overcome a car’s suspension setup and see a car roll over during sudden directional changes; this typically affected tall cars or ones with crude suspension setups but, while it is certainly possible to roll a car in extreme situations, technologies like electronic stability control have greatly reduced the chances of this occurring.

Too much body roll will make a car feel loose and imprecise when cornering. Too little body roll will result in a bone-jarring ride and may even reduce traction levels as the wheels skip over undulations instead of remaining in contact with the road surface.

Body roll can be a useful warning that you’re approaching the car’s limits of grip. Some softly sprung cars will exhibit high levels of lean before loosing grip, while sports cars may lean only slightly due to their stiffer suspension setups.

You may reasonably assume that extreme body roll is the precursor to actually rolling over, but this is not always the case. Some vehicles will roll quite noticeably through corners but will simply slide off the road when grip levels are exceeded. This is partly because a large portion of a car’s weight is low down (especially in EVs). Increasing your speed gradually through a corner will increase body lean but is unlikely to result in your car rolling over. Actually ending up on your roof is more likely to occur with sudden changes in velocity and direction, such as hitting a pothole or kerb at speed.

As a general rule, taller, heavier cars will roll more than low-slung, lighter cars. Manufacturers can also influence the way a vehicle behaves around a corner by altering the suspension and shock absorber settings.

A large, heavy SUV like a Range Rover will have more roll to give it a softer ride and lots of suspension travel to allow it to traverse off-road obstacles more easily. In comparison, a Porsche Cayenne SUV will be far firmer on the road, giving it a sportier feel at the expense of some driving comfort.

Small cars with soft suspension settings can also roll quite noticeably in corners. Cars like the classic Citroen 2CV and Renault 4 would often lean comically around every bend thanks to their overly soft suspensions. This made them great over rough roads at the expense of a sharper driving feel. A modern equivalent would be the Citroen C4, it has a comfort-biased suspension setup that gives it a superbly smooth ride, but it leans more than the sportier offerings in its class.

Factors contributing to increased body roll:

A light car that is low to the ground will have less weight to deal with when it goes around a corner. This will reduce the body roll, which can be further mitigated by using stiff suspension settings. Adaptive suspension and active anti-roll bars further reduce the tendency for the body to lean during cornering.

The very first Minis in the 1950s and ‘60s had Hydrolastic suspension systems that offered reasonable ride comfort with minimal body roll. The ‘90s Citroen Xantia was one of the first production cars to have an active suspension system. It had a hydropneumatic setup that would adjust the firmness of the suspension based on your driving style.

Applying modern developments of these sorts of technologies to the latest SUVs can often deliver a sporty driving experience that belies their size and weight. Yet applying the same electronic and mechanical trickery to a low-slung, lighter car will yield even better results. As mentioned above, a Porsche Cayenne is a superlative sporty SUV, but physics dictate that a purpose-built sports car like the Porsche 911 will exhibit less body roll as it has less centrifugal force to deal with.

While this all results in a sharp and engaging driving experience, the downside is a firmer ride. And if the suspension is made too stiff the car can feel jittery and uncomfortable on all but the smoothest road surfaces.

Factors contributing to reduced body roll:

You may feel that reducing your car rolling in the corners will be a beneficial move. As explained above, the handling characteristics of your car have been fine-tuned by the manufacturer to meet specific targets. Fiddling with these parameters will often upset the car’s inherent handling balance.

It is a far better idea to pick a car that suits your requirements in the first place. Most manufacturers offer a range of models that cater to different driving needs. In a very broad generalisation, brands like BMW and Audi will cater to the sportier end of the market, while Lexus and Volvo tend to have slightly softer suspensions, trading outright driving engagement for a more compliant ride.

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Here is a quick recap of how the weight of your vehicle shifts when you perform basic maneuvers:

You must learn how different maneuvers affect the distribution of weight across your vehicle’s four tires, to keep your balance on the road. Abrupt speed or direction changes can result in weight shifts sudden enough to throw the vehicle into a skid or cause it to turn over. The most catastrophic off-road crashes, accidents and collisions are often caused by a combination of high-speed driving and poor balance control. Any time weight is shifted away from one side of the car, there is the potential for complete loss of traction and skidding to occur, or for the wheels on that side to completely lose contact with the roadway.

For example:

Fortunately, precise steering, smooth acceleration and gradual braking can prevent loss of balance. Of course, you must also keep your vehicle in good working order and stick well within a safe speed for current roadway conditions.

When the weight of your car moves toward the front or the back, this is known as pitch. Forward pitch occurs whenever you apply the brakes, shifting the balance away from the back of the vehicle and into the front wheels. If you brake suddenly, you will notice the hood of the vehicle dipping towards the road and feel the rear of the vehicle lifting slightly. Extremely abrupt braking can result in severe rear-wheel traction loss and complete loss of directional control. Note that shifting directly from acceleration to braking (as you might if a hazard suddenly appeared in the roadway) will exaggerate the effects of the rear-to-front weight transfer.

If you are traveling along a straight stretch of road, applying the brakes gradually will keep the weight of the vehicle distributed more evenly between the four wheels, maximizing rear-wheel traction and reducing the likelihood that you will lose control.

Avoid braking when driving through a curve or bend in the road, as forward pitch could result in oversteer. As the vehicle’s weight shifts forwards, your rear wheels may lose connection with the road surface and swing out to the side as you turn. Always reduce your speed gradually, before entering a curve in the road.

Backward pitch describes the shift of weight from the front into the back wheels of the vehicle. This will occur whenever you accelerate. Rapid acceleration results in a sudden backwards pitch, causing the rear of the vehicle to dip and the hood to lift. Backward pitch cannot be avoided and will always occur to some extent when you accelerate. However, you can maintain better balance by applying gradual pressure to the accelerator, whenever you wish to pull off or increase your speed.

Avoid sudden acceleration as you approach a corner or bend in the road, as it could result in understeer. When the abrupt backward pitch reduces traction in the front tires, your attempts to steer around the curve of the road may be ineffective, causing you to drive straight off the side of the road.

Roll is the term used to describe the sideways shift of weight in a vehicle from left to right, or vice versa. Your vehicle’s balance will shift from one side to the other whenever you steer. How suddenly this shift occurs will depend on how sharply you steer and how fast you are traveling. Roll always acts in opposition to steering:

Understanding this side-to-side weight transfer can help you to become a safer and more skilled driver. Taking a corner or a bend in the road with a sudden movement of the steering wheel can lead to an abrupt sideways shift that rolls your car over if the rear wheels still have decent traction. This is even more of a danger in high-sided vehicles like SUVs and pick-up trucks which are more susceptible to rolling. However, if you steer around a corner or a bend smoothly and progressively, the gradual shift of weight toward the outside wheels can improve your grip on the road’s surface and allow you to take the corner at a higher speed, while still maintaining control.

Yaw describes a change in vehicle balance which causes the car to spin around its center of gravity (imagine this as a vertical pole through the middle of your vehicle). Like roll, yaw is the product of a sudden side-to-side weight shift caused by sharp steering. Yaw is more likely to occur on slippery surfaces when both rear tires have poor traction, causing the back end of the vehicle to spin away from the direction of the turn rather than lifting off the ground sideways.

Many maneuvers cause multi-directional weight shifts (I.e. braking while turning right shifts the balance of the car forwards and to the left, while accelerating and turning left would result in a shift backward and to the right). Understanding these effects will help you get the best performance from your vehicle while driving, as you can use them to your advantage.

Imagine you’re approaching a curve in the road and need to reduce your speed. If you enter the curve at speed and apply your brakes as you drive through it, the forward pitch and sideways roll may result in serious traction loss and a skid mid-curve. A savvy driver who understood vehicle balance would brake almost to the point of wheel lock BEFORE entering the curve, then take their foot off the brake pedal as they drive through it. The forward pitch before the curve will improve traction as they begin the turn.

Even the most skilled driver in the country may not be able to prevent a skid in a vehicle with damaged or worn-out tires. The condition of your tire tread has a dramatic effect on traction and the results of shifts in vehicle balance. Any sudden shift in weight is much more likely to lead to loss of control if your tires are old, unevenly inflated or not inflated to the manufacturer's recommended pressure. Keep your tires in good shape – it is essential to your safety!

The attribute pitch can be referred to bouncing a ball. In the car case, it is a different scene. Imagine driving in a metal rod into the side of a car such that it protrudes through a car from both horizontal ends. Now, if that rod is rotated clockwise or anticlockwise, the car will also rotate with that rod. That rotation is called pitch. Essentially, the car is flipping in a certain direction, clockwise or anticlockwise. One example of daily car pitch is braking. When a car is under braking, the weight of the car is transferred forward onto the front wheels. That makes the body of the car lean forward. Same with acceleration. The car leans back, transferring weight on the rear wheels. Now, pitch is important because it signifies the level of grip being given to tires on straight line actions, like the ones mentioned above.

Imagine a rear wheel drive car has practically no room for pitch. It doesn’t have pitch for even the hardest braking or the hardest acceleration. That would mean all four wheels would get equal brake power and acceleration. That would be a problem. Let’s take braking first. Because there is no forward pitch, the front wheels, which are the wheels that need the most grip while braking, won’t get the weight on the front they would require. This would mean lesser grip for the tires. This would result in a longer braking distance or even a skid. The next bit is acceleration. Suppose our notorious no – pitch car is in a drag race. With pitch, weight would be transferred to the rear wheels. This would help only if the vehicle was rear or all – wheel drive but who takes front – wheel drive vehicles to the drag strip anyway? ( Some do, but their cars are heavily modded for that ).

So, our car goes at full throttle. No weight falls on the rear. The weight is again equally distributed but not in a beneficial way. The rear tires scrabble for grip, but there is none to offer. Therefore, a half – baked run emerges. Now we know that pitch is important, let’s move to roll.

Roll is, well, roll. It is the movement of  a car’s body that defines how well a car can distribute its weight while turning. Another way it can be explained is this. Drive in another imaginary rod straight through the front of a car and let it emerge from the back. The clockwise & anticlockwise movement of the car and rod is what’s known as roll.

Roll is yet another important attribute of car physics. It does good things and bad things. Let’s start with the good stuff. Roll is just the shifting of weight in a car to the right or left. Entering a corner is one such example as a car tends to lean in the opposite direction of the turn. Doing so, it places a load on the outermost tires. If balanced, then it helps in dishing out more grip from tires. It is also beneficial in a motor sport : drifting. In a sharp turning maneuver, there is roll but it is excessive and literally swings a car into a drift.

The bad side. Roll is beneficial, but also harmful. Take for instance, a tall SUV going along a zigzag road at a high speed. Roll in this case will be so pronounced that the vehicle can tip on two wheels and topple over. It also causes uneven wear to tires and sometimes damages them. It also upsets people’s tummies. Seriously.

Drive the infamous rod into the top of a car ( third time’s the charm ). The clockwise or anticlockwise movement of rod and car is called yaw. Another definition of yaw is, well, turning. Here, yaw is nothing but a value. It has no force upon a car. Yet, it is very important for calculations. Now, when a car turns, all the wheels rotate at different speeds. For instance, the wheels of the car at the right side are rotating faster than the ones on the left side when the vehicle turns to the left.Why is because the wheels that are farthest from the inside of a curve cover more area than the wheels nearest to the inside line. This creates an imbalanced force and a vehicle turns due to that. It all happens due to differential boxes, but that’s a whole other story. That axial movement is yaw. The point is, the more the yaw, the sharper a car turns and vice versa for the smaller value.

I will end this post here. I will write more about cars and parts. Be sure to request your own posts.

Happy Driving!

The way your car leans to one side during cornering is called body roll. If you turn left, the car will roll to the right and vice versa.