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In both road and rail vehicles, the wheelbase is the 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 defined as the distance between the steering (front) axle and the centerpoint of the driving axle group. In the case of a tri-axle truck, the wheelbase would be the distance between the steering axle and a point midway between the two rear axles.
Wheelbase
Contents 1 Vehicles 1.1 Varying wheelbases within nameplate 1.2 Bikes 1.3 Skateboards 2 Rail 3 See also 4 References Vehicles[edit] The wheelbase of a vehicle equals the distance between its front and rear wheels. At equilibrium, the total torque of the forces acting on a vehicle is zero. Therefore, the wheelbase is related to the force on each pair of tires by the following formula: F f = d r L m g displaystyle F_ f = d_ r over L mg F r = d f L m g displaystyle F_ r = d_ f over L mg where F f displaystyle F_ f is the force on the front tires, F r displaystyle F_ r is the force on the rear tires, L displaystyle L is the wheelbase, d r displaystyle d_ r is the distance from the center of mass (CM) to the rear wheels, d f displaystyle d_ f is the distance from the center of gravity to the front wheels ( d f displaystyle d_ f + d r displaystyle d_ r = L displaystyle L ), m displaystyle m is the mass of the vehicle, and g displaystyle g is the gravity constant. So, for example, when a truck is loaded, its center of gravity shifts rearward and the force on the rear tire increases. The vehicle will ride lower. The amount the vehicle sinks will depend on counter acting forces like the size of the tires, tire pressure, and the stiffness of the suspension. If the vehicle is accelerating or decelerating, extra torque is placed on the rear or front tire respectively. The equation relating the wheelbase, height above the ground of the CM, and the force on each pair of tires becomes: F f = d r L m g − h c m L m a displaystyle F_ f = d_ r over L mg- h_ cm over L ma F r = d f L m g + h c m L m a displaystyle F_ r = d_ f over L mg+ h_ cm over L ma where F f displaystyle F_ f is the force on the front tires, F r displaystyle F_ r is the force on the rear tires, d r displaystyle d_ r is the distance from the CM to the rear wheels, d f displaystyle d_ f is the distance from the CM to the front wheels, L displaystyle L is the wheelbase, m displaystyle m is the mass of the vehicle, g displaystyle g is the acceleration of gravity (approx. 9.8 m/s2), h c m displaystyle h_ cm is the height of the CM above the ground, a displaystyle a is the acceleration (or deceleration if the value is negative). So,
as is common experience, when the vehicle accelerates, the rear
usually sinks and the front rises depending on the suspension.
Likewise, when braking the front noses down and the rear rises.:[1]
Because of the effect the wheelbase has on the weight distribution of
the vehicle, wheelbase dimensions are crucial to the balance and
steering. 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 CM. Thus, in a car with a short wheelbase,
the short lever arm from the CM 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.
Varying wheelbases within nameplate[edit]
Some luxury vehicles are offered with long-wheelbase variants to
increase the spaciousness and therefore the luxury of the vehicle.
This practice can often be found on full-size cars like the
Mercedes-Benz S-Class, but ultra-luxury vehicles such as the
Rolls-Royce Phantom and even large family cars like the
Rover 75
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 flanges 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[edit] Axle track (track)
Bicycle
References[edit] ^ Ruina, Andy; Rudra Pratap (2002). Introduction to Statics and Dynamics (PDF). Oxford University Press. p. 350. Retrieved 2007-03-23. ^ Biggs, Henry (October 27, 2004). "Rover 75". autoexpress.co.uk. Auto Express. Retrieved May 8, 2017.
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v t e Powertrain Part of the
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