![Overhang001](https://upload.wikimedia.org/wikipedia/commons/c/cf/Overhang001.svg)
Overhangs are the lengths of a
road vehicle
A vehicle (from la, vehiculum) is a machine that transports people or cargo. Vehicles include wagons, bicycles, motor vehicles (motorcycles, cars, trucks, buses, mobility scooters for disabled people), railed vehicles (trains, trams), wa ...
which extend beyond the
wheelbase
In both road and rail vehicles, the wheelbase is the horizontal distance between the centers of the front and rear wheels. For road vehicles with more than two axles (e.g. some trucks), the wheelbase is the distance between the steering (front ...
at the front and rear. They are normally described as front overhang and rear overhang. Practicality, style, and performance are affected by the size and weight of overhangs.
Characterization
Along with
clearance, length of overhangs affects the
approach and departure angles
Approach angle is the maximum angle of a ramp onto which a vehicle can climb from a horizontal plane without interference. It is defined as the angle between the ground and the line drawn between the front tire and the lowest-hanging part of the ...
, which measure the vehicle's ability to overcome steep obstacles and rough terrain. The longer the front overhang, the smaller is the approach angle, and thus lesser the car's ability to climb or descend steep ramps without damaging the front
bumpers. Typically, the rear overhang is larger on rear-wheel drive cars, while the front overhang is larger on front-wheel drive cars.
![Bogie Vehicle Schematic-en](https://upload.wikimedia.org/wikipedia/commons/c/c7/Bogie_Vehicle_Schematic-en.svg)
Overhangs in the case of
rolling stock
The term rolling stock in the rail transport industry refers to railway vehicles, including both powered and unpowered vehicles: for example, locomotives, freight and passenger cars (or coaches), and non-revenue cars. Passenger vehicles can ...
are the lengths from the
bogie pivots to the ends of the car, or in the case of two axles the distances outside of the
wheelbase
In both road and rail vehicles, the wheelbase is the horizontal distance between the centers of the front and rear wheels. For road vehicles with more than two axles (e.g. some trucks), the wheelbase is the distance between the steering (front ...
to the ends of the car.
Journalist Paul Niedermeyer has proposed an ''overhang ratio'' (OHR) to characterize the combined size of the front and rear overhangs, normalized to vehicle length, computed as
.
Because most vehicles are styled so the
wheelbase
In both road and rail vehicles, the wheelbase is the horizontal distance between the centers of the front and rear wheels. For road vehicles with more than two axles (e.g. some trucks), the wheelbase is the distance between the steering (front ...
is typically equal to four wheel+tyre diameters,
[ the minimum OHR (with no bodywork projecting beyond the front or rear wheels) is approximately 20%.
]
Advantages
Large overhangs contribute to large vehicle dimensions, and the associated advantages of size. On front-engined saloon/sedans, measuring rear overhang is helpful in predicting the size of the trunk. For these same vehicles, large front overhangs can accommodate larger engines. Large overhangs also contribute to safety
Safety is the state of being "safe", the condition of being protected from harm or other danger. Safety can also refer to the control of recognized hazards in order to achieve an acceptable level of risk.
Meanings
There are two slightly dif ...
due to increased bulk, as well as space for crumple zones
Crumple zones, crush zones, or crash zones are a structural safety feature used in vehicles, mainly in automobiles, to increase the time over which a change in velocity (and consequently momentum) occurs from the impact during a collision by ...
that provide defense for passengers in frontal and rear collisions.
The Porsche 911, produced since 1964, has always contained its entire flat-6
A flat-six engine, also known as a horizontally opposed-six, is a six-cylinder piston engine with three cylinders on each side of a central crankshaft. The most common type of flat-six engine is the boxer-six engine, where each pair of opposed cy ...
engine within its rear overhang, with the center of mass of the engine outside of the wheelbase. In the case of the 911, the rear-mounted engine allows for increased practicality in the form of a small rear row of seats that would be impossible with a mid-engined
In automotive engineering, a mid-engine layout describes the placement of an automobile engine in front of the rear-wheel axles, but behind the front axle.
History
The mid-engine, rear-wheel-drive format can be considered the original layout of ...
sports car.
Disadvantages
Excessive weight that is concentrated outside of the wheelbase can interfere with accurate negotiation of corners at high speed. The rear-engined Porsche 911, with its engine far in the rear, was notorious for dangerous oversteer
Understeer and oversteer are vehicle dynamics terms used to describe the sensitivity of a vehicle to steering. Oversteer is what occurs when a car turns (steers) by more than the amount commanded by the driver. Conversely, understeer is what occ ...
in its early days, and cars with engines far in the front often suffered from the opposite problem of understeer
Understeer and oversteer are vehicle dynamics terms used to describe the sensitivity of a vehicle to steering. Oversteer is what occurs when a car turns (steers) by more than the amount commanded by the driver. Conversely, understeer is what occ ...
, for which many old American cars with heavy V8 engine
A V8 engine is an eight-cylinder piston engine in which two banks of four cylinders share a common crankshaft and are arranged in a V configuration.
The first V8 engine was produced by the French Antoinette company in 1904, developed and u ...
s were infamous. Front-engined Ferraris, such as the Ferrari 612 Scaglietti
The Ferrari 612 Scaglietti (Type F137) () is an executive 2+2 coupé grand tourer manufactured by Italian automobile manufacturer Ferrari between 2004 and 2010. It was designed to replace the smaller 456; its larger size makes it a true 4 sea ...
place their engines within the wheelbase, so as to avoid the problem of understeer. Reducing overhanging weight in sports car
A sports car is a car designed with an emphasis on dynamic performance, such as handling, acceleration, top speed, the thrill of driving and racing capability. Sports cars originated in Europe in the early 1900s and are currently produced by ...
s is usually a priority, with the notable exception of the 911.
In contrast, the excellent handling of the Mini, with its wheels pushed far out at each corner, can be partly credited to its small overhang. The classic Mini and New MINI are both automobiles with very little overhang and thus handle very well under extreme conditions. The minimal overhang gives the Mini its bulldog-like stance.
Rear overhang may present a problem in large vehicles such as buses. Long rear overhang would require the driver to pay attention to nearby vehicles when turning at 90 degrees. Since the rear overhang is outside the wheelbase, it may hit a vehicle in the adjacent lane, especially when turning 90 degrees right (in a right-hand drive country).
Also, some specialized vehicles (such as the AM General HMMWV and the related Hummer H1
The Hummer H1 is a four-wheel-drive utility vehicle based on the M998 Humvee, which was developed by AM General when it was a subsidiary of American Motors Corporation (AMC). Originally designed strictly for military use, the off-road vehicle was ...
) are designed with no frontal overhang, allowing it to possess incredible abilities such as climbing vertical walls. This does, however, place these vehicles' front wheels as the furthest forward point of the vehicle, which can lead to disastrous results in the event of a frontal collision.
See also
* Approach and departure angles
Approach angle is the maximum angle of a ramp onto which a vehicle can climb from a horizontal plane without interference. It is defined as the angle between the ground and the line drawn between the front tire and the lowest-hanging part of the ...
* Cantilever
A cantilever is a rigid structural element that extends horizontally and is supported at only one end. Typically it extends from a flat vertical surface such as a wall, to which it must be firmly attached. Like other structural elements, a cant ...
* Idler flatcar
* Minimum railway curve radius
* Ride height
Ride height or ground clearance is the amount of space between the base of an automobile tire and the lowest point of the automobile (typically the axle); or, more properly, to the shortest distance between a flat, level surface, and the lowest p ...
* Turning diameter
The turning diameter of a vehicle is the minimum diameter (or "width") of available space required for that vehicle to make a circular turn (i.e. U-turn). The term thus refers to a theoretical minimal circle in which for example an aeroplane, a ...
* Wheelbase
In both road and rail vehicles, the wheelbase is the horizontal distance between the centers of the front and rear wheels. For road vehicles with more than two axles (e.g. some trucks), the wheelbase is the distance between the steering (front ...
References
External links
Ideal handling characteristics
{{CarDesign nav
Vehicle design