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Wheelbase
 
 
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In both road and rail vehicle
Vehicle

Vehicles, derived from the Latin word, vehiculum, are non-living means of transport. Most often they are manufactured , although some other means of transport which are not made by humans also may be called vehicles; examples include icebergs and floating tree trunks....
s, the wheelbase is the distance between the centers of the front and rear wheels.
Road
In automobile
Automobile

An automobile or motor car is a wheeled motor vehicle for transportation passengers, which also carries its own car engine or motor. Most definitions of the term specify that automobiles are designed to run primarily on roads, to have seating for one to eight people, to typically have four wheels, and to be constructed principally f...
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 is the tendency of a force to rotate an object about an axis . 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 weight
Weight

In the physical sciences, weight is a measurement of the gravitational force acting on an object. Near the surface of the Earth, the Earth's gravity is approximately constant; this means that an object's weight is roughly proportional to its mass....
 on each tire by the following formulae:

where is the weight on the front tire, is the weight on the rear tire, is the wheelbase, is the distance from the center of gravity (CG) to the rear wheel, is the distance from the center of gravity to the front wheel ( + = ), is the mass
Mass

In physical science, mass refers to the degree of acceleration a body acquires when subject to a force: bodies with greater mass are accelerated less by the same force....
 of the car, and is the gravity constant
Standard gravity

Standard gravity, usually denoted by g0 or gn, is the nominal acceleration due to Earth's gravity at the Earth's surface at sea level....
.






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In both road and rail vehicle
Vehicle

Vehicles, derived from the Latin word, vehiculum, are non-living means of transport. Most often they are manufactured , although some other means of transport which are not made by humans also may be called vehicles; examples include icebergs and floating tree trunks....
s, the wheelbase is the distance between the centers of the front and rear wheels.

Road


In automobile
Automobile

An automobile or motor car is a wheeled motor vehicle for transportation passengers, which also carries its own car engine or motor. Most definitions of the term specify that automobiles are designed to run primarily on roads, to have seating for one to eight people, to typically have four wheels, and to be constructed principally f...
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 is the tendency of a force to rotate an object about an axis . 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 weight
Weight

In the physical sciences, weight is a measurement of the gravitational force acting on an object. Near the surface of the Earth, the Earth's gravity is approximately constant; this means that an object's weight is roughly proportional to its mass....
 on each tire by the following formulae:

where is the weight on the front tire, is the weight on the rear tire, is the wheelbase, is the distance from the center of gravity (CG) to the rear wheel, is the distance from the center of gravity to the front wheel ( + = ), is the mass
Mass

In physical science, mass refers to the degree of acceleration a body acquires when subject to a force: bodies with greater mass are accelerated less by the same force....
 of the car, and is the gravity constant
Standard gravity

Standard gravity, usually denoted by g0 or gn, is the nominal acceleration due to Earth's gravity at the Earth's surface at sea level....
. So, for example, when one loads the trunk with heavy goods, the center of gravity shifts rearward and the weight on the rear tire increases causing it to sink depending upon the stiffness of the suspension
Suspension (vehicle)

Suspension is the term given to the system of spring , shock absorbers and Linkage that connects a vehicle to its wheels. Suspension systems serve a dual purpose ? contributing to the car's car handling and brake for good active safety and driving pleasure, and keeping vehicle occupants comfortable and reasonably well isolated from road no...
. If the automobile is accelerating or decelerating, extra torque is placed on the rear or front tire
Tire

Tires, or tyres , are ring-shaped parts, either pneumatic or solid , that fit around wheels to protect them and enhance their function....
 respectively, and the equation relating the wheelbase, height above the ground of the CG, and the weight on each tire becomes:

where is the weight on the front tire, is the weight on the rear tire, is the distance from the CG to the rear wheel, is the distance from the CG to the front wheel, 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 transfer of the vehicle, wheelbase dimensions are crucial to the balance and steering of the automobile. For example, a car
Automobile

An automobile or motor car is a wheeled motor vehicle for transportation passengers, which also carries its own car engine or motor. Most definitions of the term specify that automobiles are designed to run primarily on roads, to have seating for one to eight people, to typically have four wheels, and to be constructed principally f...
 with a much greater weight load on the rear tends to understeer
Understeer

Understeer is a term for a car handling condition in which during cornering the circular path of the vehicle's motion is of a greater radius than the circle indicated by the direction its wheels are pointed....
 due to the lack of weight and therefore grip from the front tires. 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
Oversteer

Oversteer is a phenomenon that can occur in an automobile while attempting to corner or while already cornering. The car is said to oversteer when the rear wheels do not track behind the front wheels but instead slide out toward the outside of the turn....
 or even "spin out" if there is too much weight 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 that which can cause an object with mass to change its velocity. Force has both Euclidean_vector#Length of a vector and Direction , making it a Vector quantity....
 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.

Bikes


The wheelbase
Bicycle and motorcycle geometry

Bicycle 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....
 on many commercially available bicycle
Bicycle

The bicycle, bike, or cycle is a pedal-driven, human-powered transport with two bicycle wheel attached to a bicycle frame, one behind the other....
s and motorcycle
Motorcycle

A motorcycle is a Single track, two-wheeled motor vehicle powered by an Motorcycle engine. Motorcycles vary considerably depending on the task for which they are designed, such as Touring motorcycle travel, navigating Naked bike, Cruiser , Motorcycle sport and Motorbike racing, or off-road conditions....
s is so short, relative to the height of their centers of mass, that they are able to perform stoppie
Stoppie

The stoppie, also incorrectly called endo, 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....
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....
s.

Rail


In rail vehicles, the wheelbase follows a similar concept.

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 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 Machine 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 or locomotive, or sprung as in the suspension of a caterpillar tracked vehicle....
, 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 rib, or rim , for Shear strength, as the flange of an iron Beam or I-beam ; or for a guide, as the flange of a train wheel; 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....
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

  • Bicycle and motorcycle geometry
    Bicycle and motorcycle geometry

    Bicycle 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 gravity
  • force
    Force

    In physics, a force is that which can cause an object with mass to change its velocity. Force has both Euclidean_vector#Length of a vector and Direction , making it a Vector quantity....
  • static equilibrium
  • torque
    Torque

    Torque is the tendency of a force to rotate an object about an axis . Just as a force is a push or a pull, a torque can be thought of as a twist....
  • weight
    Weight

    In the physical sciences, weight is a measurement of the gravitational force acting on an object. Near the surface of the Earth, the Earth's gravity is approximately constant; this means that an object's weight is roughly proportional to its mass....