Wheelbase
Encyclopedia
In both road and rail vehicle
s, the wheelbase is the distance between the centers of the front and rear wheels.
s, the wheelbase is the horizontal distance between the center of the front wheel and the center of the rear wheel. At equilibrium, the total torque
of the forces acting on the car is zero, and thus the wheelbase is related to the force
on each pair of tires by the following formula:
where
is the force on the front tires, 
is the force on the rear tires, 
is the wheelbase, 
is the distance from the center of gravity
(CG) to the rear wheels,
is the distance from the center of gravity to the front wheels (
+ 
= 
), 
is the mass
of the car, and
is the gravity constant
. So, for example, when one loads the truck with heavy goods, the center of gravity shifts rearward and the force on the rear tire increases causing it to sink to the extent that depends on the stiffness of the suspension
.
If the automobile is accelerating or decelerating, extra torque is placed on the rear or front tire
respectively, and the equation relating the wheelbase, height above the ground of the CG, and the force on each pair of tires becomes:
where
is the force on the front tires, 
is the force on the rear tires, 
is the distance from the CG to the rear wheels, 
is the distance from the CG to the front wheels, 
is the wheelbase, 
is the mass of the car, 
is the acceleration of gravity (approx. 9.8 m/s2), 
is the height of the CG above the ground, 
is the acceleration (or deceleration if the value is negative). So, as is common experience, when the automobile accelerates, the rear usually sinks and the front rises depending on the suspension. Likewise, when braking the front noses down and the rear rises.:
Because of the effect the wheelbase has on the weight distribution of the vehicle, wheelbase dimensions are crucial to the balance and steering of the automobile. For example, a car
with a much greater weight load on the rear tends to understeer
due to the lack of the load (force) on the front tires and therefore the grip (friction
) from them. This is why it is crucial, when towing a single-axle caravan, to distribute the caravan's weight so that down-thrust on the tow-hook is about 100 pounds force (400 N). Likewise, a car may oversteer or even "spin out" if there is too much force on the front tires and not enough on the rear tires. Also, when turning there is lateral torque placed upon the tires which imparts a turning force that depends upon the length of the tire distances from the CG. Thus, in a car with a short wheelbase, the short lever arm from the CG to the rear wheel will result in a greater lateral force
on the rear tire which means greater acceleration and less time for the driver to adjust and prevent a spin out or worse.
Wheelbases provide the basis for one of the most common vehicle size class
systems.
s such as the Jaguar XJ
, Ford Crown Victoria
, Lexus LS
, BMW 7-Series, Audi A8
and Mercedes-Benz S-Class
have had long wheelbase variants.
In contrast, coupe varieties of the Honda Accord
, and Honda Civic
usually have shorter wheelbases than the sedans that they were derived from.
s and motorcycle
s is so short, relative to the height of their centers of mass
, that they are able to perform stoppie
s and wheelie
s.
A common misconception is that the choice of wheelbase is influenced by the height of the skateboarder. However, the length of the deck would then be a better candidate, because the wheelbase affects characteristics useful in different speeds or terrains regardless of the height of the skateboarder. For example, a deck with a long wheelbase, say 16 inches (406.4 mm), will respond slowly to turns, which is often desirable in high speeds. A deck with a short wheelbase, say 14 inches (355.6 mm), will respond quickly to turns, which is often desirable when skating backyard pools or other terrains requiring quick or intense turns.
), the measurement is taken between the points where the wheels contact the rail, and not between the centers of the wheels.
On vehicles where the wheelsets (axles)
are mounted inside the vehicle frame (mostly in steam locomotives), the wheelbase is the distance between the front-most and rear-most wheelsets.
On vehicles where the wheelsets are mounted on bogies (amer.: trucks)
, three wheelbase measurements can be distinguished:
The wheelbase affects the rail vehicle's capability to negotiate curves. Short-wheelbased vehicles can negotiate sharper curves. On some larger wheelbase locomotives, inner wheels may lack flange
s in order to pass curves.
The wheelbase also affects the load the vehicle poses to the track, track infrastructure and bridges. All other conditions being equal, a shorter wheelbase vehicle represents a more concentrated load to the track than a longer wheelbase vehicle. As railway lines are designed to take a pre-determined maximum load per unit of length (tonnes per meter, or pounds per foot), the rail vehicles' wheelbase is designed according to their intended gross weight. The higher the gross weight, the longer the wheelbase must be.
Vehicle
A vehicle is a device that is designed or used to transport people or cargo. Most often vehicles are manufactured, such as bicycles, cars, motorcycles, trains, ships, boats, and aircraft....
s, the wheelbase is the distance between the centers of the front and rear wheels.
Road
In automobileAutomobile
An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...
s, the wheelbase is the horizontal distance between the center of the front wheel and the center of the rear wheel. At equilibrium, the total torque
Torque
Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
of the forces acting on the car is zero, and thus the wheelbase is related to the force
Force
In physics, a force is any influence that causes an object to undergo a change in speed, a change in direction, or a change in shape. In other words, a force is that which can cause an object with mass to change its velocity , i.e., to accelerate, or which can cause a flexible object to deform...
on each pair of tires by the following formula:
where
is the force on the front tires, is the force on the rear tires, is the wheelbase, is the distance from the center of gravityCenter of gravity
In physics, a center of gravity of a material body is a point that may be used for a summary description of gravitational interactions. In a uniform gravitational field, the center of mass serves as the center of gravity...
(CG) to the rear wheels,
is the distance from the center of gravity to the front wheels ( + = ), is the massMass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
of the car, and
is the gravity constantStandard gravity
Standard gravity, or standard acceleration due to free fall, usually denoted by g0 or gn, is the nominal acceleration of an object in a vacuum near the surface of the Earth. It is defined as precisely , or about...
. So, for example, when one loads the truck with heavy goods, the center of gravity shifts rearward and the force on the rear tire increases causing it to sink to the extent that depends on the stiffness of the suspension
Suspension (vehicle)
Suspension is the term given to the system of springs, shock absorbers and linkages that connects a vehicle to its wheels. Suspension systems serve a dual purpose — contributing to the car's roadholding/handling and braking for good active safety and driving pleasure, and keeping vehicle occupants...
.
If the automobile is accelerating or decelerating, extra torque is placed on the rear or front tire
Tire
A tire or tyre is a ring-shaped covering that fits around a wheel rim to protect it and enable better vehicle performance by providing a flexible cushion that absorbs shock while keeping the wheel in close contact with the ground...
respectively, and the equation relating the wheelbase, height above the ground of the CG, and the force on each pair of tires becomes:
where
is the force on the front tires, is the force on the rear tires, is the distance from the CG to the rear wheels, is the distance from the CG to the front wheels, is the wheelbase, is the mass of the car, is the acceleration of gravity (approx. 9.8 m/s2), is the height of the CG above the ground, is the acceleration (or deceleration if the value is negative). So, as is common experience, when the automobile accelerates, the rear usually sinks and the front rises depending on the suspension. Likewise, when braking the front noses down and the rear rises.:Because of the effect the wheelbase has on the weight distribution of the vehicle, wheelbase dimensions are crucial to the balance and steering of the automobile. For example, a car
Automobile
An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...
with a much greater weight load on the rear tends to understeer
Understeer
Understeer and oversteer are vehicle dynamics terms used to describe the sensitivity of a vehicle to steering. Simply put, oversteer is what occurs when a car turns by more than the amount commanded by the driver...
due to the lack of the load (force) on the front tires and therefore the grip (friction
Friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...
) from them. This is why it is crucial, when towing a single-axle caravan, to distribute the caravan's weight so that down-thrust on the tow-hook is about 100 pounds force (400 N). Likewise, a car may oversteer or even "spin out" if there is too much force on the front tires and not enough on the rear tires. Also, when turning there is lateral torque placed upon the tires which imparts a turning force that depends upon the length of the tire distances from the CG. Thus, in a car with a short wheelbase, the short lever arm from the CG to the rear wheel will result in a greater lateral force
Force
In physics, a force is any influence that causes an object to undergo a change in speed, a change in direction, or a change in shape. In other words, a force is that which can cause an object with mass to change its velocity , i.e., to accelerate, or which can cause a flexible object to deform...
on the rear tire which means greater acceleration and less time for the driver to adjust and prevent a spin out or worse.
Wheelbases provide the basis for one of the most common vehicle size class
Vehicle size class
Vehicle size classes are a way of classifying cars. The common North American parlance is word-based, while English-speaking European writers also use words to describe car sizes...
systems.
Varying wheelbases within nameplate
Full-size carFull-size car
A full-size car is a marketing term used in North America for an automobile larger than a mid-size car. In the United States, the EPA uses "large car" to denote full-size cars....
s such as the Jaguar XJ
Jaguar XJ
Jaguar XJ is the designation that has been used for a series of luxury saloon cars sold under the British Jaguar marque. The first XJ was launched in 1968 and the designation has been used for successive Jaguar flagship models since then. The original model was the last Jaguar saloon to have had...
, Ford Crown Victoria
Ford Crown Victoria
-1992–1994:Released in March 1991 as an early 1992 model, the Crown Victoria sedan was completely redesigned with a rounder, eight-window roofline . The redesign reduced the coefficient of drag from 0.42 to 0.34; the suspension setup was also heavily revised...
, Lexus LS
Lexus LS
The Lexus LS is a full-size luxury sedan that serves as the flagship model of Lexus, the luxury division of Toyota. Four generations of the sedan have been produced, all equipped with V8 engines and rear-wheel drive, although since 2006 all-wheel drive, hybrid, and long-wheelbase variants have also...
, BMW 7-Series, Audi A8
Audi A8
The Audi A8 is a four-door, full-size, luxury sedan car manufactured and marketed by the German automaker Audi since 1994. Succeeding the Audi V8, the A8 has been offered with front wheel drive or permanent four-wheel drive, with multitronic or tiptronic automatic transmissions — and in short- and...
and Mercedes-Benz S-Class
Mercedes-Benz S-Class
The Mercedes-Benz S-Class is a series of luxury sedans produced by Mercedes-Benz, a division of Daimler AG. The classification was officially introduced in 1972 with the W116 S-Class, which succeeded previous Mercedes-Benz models dating to the mid-1950s...
have had long wheelbase variants.
In contrast, coupe varieties of the Honda Accord
Honda Accord
The Honda Accord is a series of compact, mid-size and full-size automobiles manufactured by Honda since 1976, and sold in a majority of automotive markets throughout the world....
, and Honda Civic
Honda Civic
The Honda Civic is a line of subcompact and subsequently compact cars made and manufactured by Honda. The Civic, along with the Accord and Prelude, comprised Honda's vehicles sold in North America until the 1990s, when the model lineup was expanded...
usually have shorter wheelbases than the sedans that they were derived from.
Bikes
The wheelbase on many commercially available bicycleBicycle
A bicycle, also known as a bike, pushbike or cycle, is a human-powered, pedal-driven, single-track vehicle, having two wheels attached to a frame, one behind the other. A person who rides a bicycle is called a cyclist, or bicyclist....
s and motorcycle
Motorcycle
A motorcycle is a single-track, two-wheeled motor vehicle. Motorcycles vary considerably depending on the task for which they are designed, such as long distance travel, navigating congested urban traffic, cruising, sport and racing, or off-road conditions.Motorcycles are one of the most...
s is so short, relative to the height of their centers of mass
Center of gravity
In physics, a center of gravity of a material body is a point that may be used for a summary description of gravitational interactions. In a uniform gravitational field, the center of mass serves as the center of gravity...
, that they are able to perform stoppie
Stoppie
The stoppie , is a motorcycle and bicycle trick in which the back wheel is lifted and the bike is ridden on the front wheel by carefully applying brake pressure. It is also sometimes called a front wheelie.-General description:...
s and wheelie
Wheelie
In vehicle acrobatics, a wheelie is a vehicle maneuver in which the front wheel or wheels come off the ground due to extreme torque being applied to the rear wheel or wheels. Wheelies are usually associated with bicycles and motorcycles, but can be done with other vehicles such as cars, especially...
s.
Skateboards
In skateboarding the word 'wheelbase' is used for the distance between the two inner pairs of mounting holes on the deck. This is different than the distance between the rotational centers of the two wheel pairs. A reason for this alternative use is that decks are sold with prefabricated holes, but usually without trucks and wheels. It is therefore easier to use the prefabricated holes for measuring and describing this characteristic of the deck.A common misconception is that the choice of wheelbase is influenced by the height of the skateboarder. However, the length of the deck would then be a better candidate, because the wheelbase affects characteristics useful in different speeds or terrains regardless of the height of the skateboarder. For example, a deck with a long wheelbase, say 16 inches (406.4 mm), will respond slowly to turns, which is often desirable in high speeds. A deck with a short wheelbase, say 14 inches (355.6 mm), will respond quickly to turns, which is often desirable when skating backyard pools or other terrains requiring quick or intense turns.
Rail
In rail vehicles, the wheelbase follows a similar concept. However, since the wheels may be of different sizes (for example, on a steam locomotiveSteam locomotive
A steam locomotive is a railway locomotive that produces its power through a steam engine. These locomotives are fueled by burning some combustible material, usually coal, wood or oil, to produce steam in a boiler, which drives the steam engine...
), the measurement is taken between the points where the wheels contact the rail, and not between the centers of the wheels.
On vehicles where the wheelsets (axles)
Wheelset (railroad)
A wheelset is the wheel-axle assembly of a railroad car. The frame assembly beneath each end of a car, railcar or locomotive that holds the wheelsets is called the bogie...
are mounted inside the vehicle frame (mostly in steam locomotives), the wheelbase is the distance between the front-most and rear-most wheelsets.
On vehicles where the wheelsets are mounted on bogies (amer.: trucks)
Bogie
A bogie is a wheeled wagon or trolley. In mechanics terms, a bogie is a chassis or framework carrying wheels, attached to a vehicle. It can be fixed in place, as on a cargo truck, mounted on a swivel, as on a railway carriage/car or locomotive, or sprung as in the suspension of a caterpillar...
, three wheelbase measurements can be distinguished:
- the distance between the pivot points of the front-most and rear-most bogie;
- the distance between the front-most and rear-most wheelsets of the vehicle;
- the distance between the front-most and rear-most wheelsets of each bogie.
The wheelbase affects the rail vehicle's capability to negotiate curves. Short-wheelbased vehicles can negotiate sharper curves. On some larger wheelbase locomotives, inner wheels may lack flange
Flange
A flange is an external or internal ridge, or rim , for strength, as the flange of an iron beam such as an I-beam or a T-beam; or for attachment to another object, as the flange on the end of a pipe, steam cylinder, etc., or on the lens mount of a camera; or for a flange of a rail car or tram wheel...
s in order to pass curves.
The wheelbase also affects the load the vehicle poses to the track, track infrastructure and bridges. All other conditions being equal, a shorter wheelbase vehicle represents a more concentrated load to the track than a longer wheelbase vehicle. As railway lines are designed to take a pre-determined maximum load per unit of length (tonnes per meter, or pounds per foot), the rail vehicles' wheelbase is designed according to their intended gross weight. The higher the gross weight, the longer the wheelbase must be.
See also
- Axle track
- Bicycle and motorcycle geometryBicycle and motorcycle geometryBicycle and motorcycle geometry is the collection of key measurements that define a particular bike configuration. Primary among these are wheelbase, steering axis angle, fork offset, and trail...
- Center of gravityCenter of gravityIn physics, a center of gravity of a material body is a point that may be used for a summary description of gravitational interactions. In a uniform gravitational field, the center of mass serves as the center of gravity...
- ForceForceIn physics, a force is any influence that causes an object to undergo a change in speed, a change in direction, or a change in shape. In other words, a force is that which can cause an object with mass to change its velocity , i.e., to accelerate, or which can cause a flexible object to deform...
- Static equilibrium
- TorqueTorqueTorque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
- WeightWeightIn science and engineering, the weight of an object is the force on the object due to gravity. Its magnitude , often denoted by an italic letter W, is the product of the mass m of the object and the magnitude of the local gravitational acceleration g; thus:...