What Are Approach, Breakover, and Departure Angles?

Treading the ups and downs of unpaved terrain or climbing over obstacles are not general concerns in everyday driving. But when it comes to off-roading, the story changes drastically. Understanding a vehicle's capabilities to go up and over an object or an incline is vital to the off-road driving experience. As such, three essential vehicle characteristics come into play: approach, breakover, and departure angles. Being familiar with each is critical before heading off-pavement and into the wild. This article explains what these angles are and why they're important.

Photo: Driver Knowledge Test (DKT) Resources

Why Are Approach, Breakover, and Departure Angles Important?

These three measurements are relevant for climbing up or down steep inclines and getting over ruts, rises, logs, rocks, and boulders, among other objects an off-roader may encounter. Since the terrain on a trail can be unpredictable and ever-changing, knowing these three angles will give the driver a better sense of what obstacles they can and can't tackle. Calculating these angles requires taking distance measurements and applying trigonometric formulas. For those who need help remembering these equations from high school, there are a number of helpful online angle calculators to determine all three measurements.

What Is a Vehicle's Approach Angle?

The approach angle is defined as the angle between the front tires touching the ground and the lowest part of the front of the car, usually the front bumper. The approach angle determines how steep of an obstacle you can climb or descend without your bumper or other portions of the frame contacting the obstacle or the ground. If the approach angle is adequate, there will be bumper clearance for the front tires to reach the incline and begin climbing.

The vehicle nose length, or the distance the front of the car extends beyond the front wheels, is the most telling feature of a vehicle's approach angle. Typically, the shorter the nose on a car, the steeper the approach angle. This means a vehicle can take on steeper inclines or climbs. Conversely, a long nose or protruding bumper makes for a shallower approach angle. The shallower the angle, the greater the chance the vehicle's front end will strike the incline before the tires reach the incline. However, other vehicle design factors, aside from vehicle nose length, will affect the approach angle:

• Tire size—Larger tires lift the vehicle further from the ground and increase the approach angle, enabling the car to attack steeper inclines. Smaller or lower-profile tires will reduce the vehicle's approach angle.
• Suspension—A suspension that lifts the chassis higher off the ground will improve the approach angle. This is why many off-road vehicles are "lifted."
• Front-mounted winch—Winches that hang below the front bumper will drastically reduce the vehicle's approach angle. A front-mounted winch is a better option, but it will still extend the vehicle's nose and reduce the approach angle.

To calculate the approach angle of a vehicle, you will need two measurements: the distance from the lowest point under the front of the car to level ground and the distance from where the leading edge of the front wheel touches the ground to the lowest point under the vehicle's front. The formula to solve this is:

tan-1(ground clearance/distance between tire and vehicle nose)

A more straightforward approach is to plug these numbers into an online approach angle calculator.

What Is a Vehicle's Breakover Angle?

Photo: Traxxas.com

The official definition of the breakover angle is the maximum supplementary angle that the vehicle can traverse such that when one set of wheels are on one side of the apex and the trailing wheels on the other side of the apex, the apex of the peak does not touch the underside of the vehicle. The breakover angle will influence the height of a peak it can summit, considering the steepness of the angle on either side of the peak. This information will prevent a vehicle from getting stuck on a pivot point with one or both sets of wheels off the ground.

The breakover angle is often incorrectly mistaken for ground clearance, but they differ. Ground clearance is the distance from the ground to the lowest point on the vehicle's underside and does not consider angles or peaks. Ground clearance only factors in flat ground and will affect the depth at which you can drive the vehicle through deep ruts without scraping its underside. The breakover angle takes the slopes on either side of the peak into account to ensure the bottom of the vehicle will clear the apex of the peak. Several factors will affect the breakover angle:

• Ground clearance—The greater the ground clearance, the greater the breakover angle.
• Wheelbase—The longer the wheelbase, the lower the breakover angle. Conversely, the shorter the wheelbase, the higher the breakover angle.
• Suspension—Impacts the vehicle height and ground clearance. The higher the lift, the steeper the breakover angle.
• Tire size—The size of the tires affects vehicle height and ground clearance, thus affecting the breakover angle.
• Low-hanging components—Any components installed under the vehicle's body extending below the chassis' bottom will lower the vehicle's ground clearance and result in a shallower breakover angle.

To calculate the breakover angle, you will need the vehicle's ground clearance and wheelbase length. Then plug those numbers into this formula:

2 x arctan(2 x ground clearance/wheelbase)

Or use one of many online breakover angle calculators.

What Is a Vehicle's Departure Angle?

The departure angle is the same as the approach angle but at the vehicle's rear. It will determine how steep of an angle your car can climb so that your rear bumper doesn't hit the ground as your back tires ascend onto a slope. Or, if you are descending, it defines how steep of an obstacle you can drive down without your bumper hitting the obstacle as your tires come down onto level ground. The departure angle is the angle between ground level and a line drawn from where the back tire touches the ground to the lowest point on the car's rear.

Vehicle characteristics similar to those that affect the approach angle affect the departure angle:

• Length of the rear end—The further a vehicle's rear end extends past the rear wheels, the lower the departure angle. A shorter back end will provide a higher departure angle for exiting steeper slopes or obstacles.
• Tire size on the rear wheels—Larger tires result in a steeper departure angle. Low-profile tires or small tires will reduce the departure angle.
• Suspension—A suspension that lifts the chassis higher off the ground will improve the approach angle.
• Tow hitch—Like winches below the front bumper, tow hitches below the rear bumper will reduce the approach angle of the car. A tow hitch will also extend the rear of the vehicle, thus reducing the departure angle.

Calculating the departure angle is the same as calculating the approach angle. It considers two measurements: the distance from the lowest point under the back of the vehicle to level ground and the distance from where the back edge of the back wheel touches the ground to the lowest point under the vehicle's rear. The formula for solving this is the same as that of an approach angle (see approach angle section). But again, an online calculator will be a faster way to calculate a vehicle's departure angle.

Summary

Navigating the challenges of off-road driving requires knowledge of a vehicle's capabilities to traverse the ups and downs of unpaved terrain. To that end, having a sense of a vehicle's approach angle, breakover angle, and departure angle is essential to a safe and enjoyable off-road experience.

Jessica Shea Choksey is an experienced writer in the automotive field. In addition to JDPower.com, she was a correspondent for PBS's MotorWeek. Her work has also appeared in AutoTrader.

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