What is g-force and how is it related to harsh driving?

A question we get asked frequently is: “How do g-force values relate to real world driving habits?”

In fleet management software like MyGeotab, harsh driving — when accelerating, cornering or braking, for example — is defined in terms of g-force.

G-force and acceleration

Before we get to the software, let’s talk about g-force. A g-force is a measure of acceleration. 1G is the acceleration we feel due to the force of gravity. It’s what keeps our feet firmly planted on the ground. Gravity is measured in metres per second squared, or m/s2. On Earth, the acceleration of gravity generally has a value of 9.806 m/s2 or 32.1740 f/s2. Since this is just a different scale for measuring acceleration, it not only applies to gravity, but can be used to quantify any acceleration.

See also: What is a connected car

How g-force relates to harsh driving

As mentioned, you can configure the Geotab telematics Device to produce immediate audible feedback in response to excessive driving behaviors such as harsh acceleration, harsh braking, and harsh cornering. You can access the settings from Vehicle Edit > Driver Feedback tab.

When setting up harsh driving rules in MyGeotab, adjusting the level of sensitivity will affect when feedback is given for a harsh driving event — either a beep or a spoken alert if you have GO TALK installed. A smaller number (e.g. -0.47 G) is more sensitive and means the rule is easier to break. A larger number (e.g. -0.61 G) is less sensitive, meaning that only the most aggressive driving events will break the rule, triggering driver feedback. Moving the slider to the right increases the sensitivity of monitoring.

Accelerometer Driver Feedback Settings set to Least sensitive (Passenger Car.)

Accelerometer Driver Feedback Settings set to Most sensitive (Heavy-Duty.)

It’s also important to mention that since this is an acceleration and not a force, the vehicle’s mass or size doesn’t matter at all. In the harsh driving rules, we specify the vehicle size (passenger car, truck/cube van, and heavy-duty truck) as a suggestion. A sports car can safely take a corner faster than a truck.

For a table of the average g-force exertions for various vehicle classes, see the Geotab Product Guide.

Recommendations for setting up driver feedback

When configuring settings, we suggest beginning with the standard parameters for your specific vehicle class. From there, adjustments should be made to align with your fleet's unique operational needs and safety goals. For instance, if your objective is to decrease harsh driving incidents, you can opt for higher sensitivity levels. This is particularly useful for specialized vehicles, such as ambulances transporting patients, where high sensitivity is vital for safety. Conversely, for vehicles hauling less sensitive cargo, like a box truck filled with paper towels, a lower sensitivity setting may be more appropriate.

By evaluating the three primary harsh driving metrics, you can determine the specific thresholds—such as cornering speed or acceleration from a stop—that trigger a rule violation. These critical G-force events serve as the technical basis for https://www.geotab.com/vitality/'s driver incentive program. Using the same telematics data discussed in this article, Geotab Vitality monitors daily instances of harsh braking, cornering, and acceleration, providing drivers with financial rewards for safer performance. 

Harsh acceleration and harsh braking

The harsh acceleration and harsh braking rules are really the same thing and measure how quickly you are speeding up or slowing down. The least sensitive setting in the default rule for acceleration is 0.43 Gs which is what a driver (or Geotab GO device) would experience if you accelerated from standstill to 60 km/h in 3.95 seconds. The braking rule is even more lenient and would require that you come to a complete stop from 60 km/h in 2.78 seconds, deccelerating at 0.61 Gs.

To get a better understanding of linear acceleration and g-forces, check out this handy Acceleration Calculator.

Harsh cornering

Harsh cornering is a little trickier to both calculate and grasp intuitively. Any time you change velocity you are undergoing an acceleration. When you are turning a corner, this acceleration is 90 degrees from the direction you are traveling, regardless of how tight a turn you are making. Think about spinning a weight on the end of a string. You are always pulling the weight towards your hand but it never gets any closer.

So how do we measure this? To determine the acceleration you experience in a corner, all we need is the radius of the corner and your speed. I measured the radius of a normal right turn at an intersection of two four-lane roads and found it to be about 17 metres. This means that if it went through this corner at 32 km/h you would break the most lenient harsh cornering rule which is set at 0.47 Gs.

If you want to play with the number yourself, you can find a centrifugal force calculator here for accelerations in a corner.

Note: You do not need to input an angular speed or mass to calculate g-force.

See also:

What is telematics

Distracted driving facts: Common causes and solutions