Progressive shifting is a technique for changing gears commonly practiced by
drivers of
semi-trailer truck
A semi-trailer truck, also known as a semitruck, (or semi, eighteen-wheeler, big rig, tractor-trailer or, by synecdoche, a semitrailer) is the combination of a tractor unit and one or more semi-trailers to carry freight. A semi-trailer ...
s. It is meant to reduce
fuel
A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy or to be used for work. The concept was originally applied solely to those materials capable of releasing chemical energy but ...
consumption — something very important for drivers who travel several hundred miles each day.
Progressive shifting is accomplished by changing gears upward as early as possible when accelerating, while staying within the flat torque range. Each shift will go a little higher into the RPM, until the vehicle is in its top gear at cruising speed. After each shift is completed, the
engine
An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy.
Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power gen ...
and
transmission should be operating at or near the lowest
rpm
Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or with the notation min−1) is a unit of rotational speed or rotational frequency for rotating machines.
Standards
ISO 80000-3:2019 defines a unit of rotation as the dimensionl ...
speeds recommended by the manufacturers of those parts.
The fastest acceleration is achieved when the truck is receiving as close as possible to maximum
power
Power most often refers to:
* Power (physics), meaning "rate of doing work"
** Engine power, the power put out by an engine
** Electric power
* Power (social and political), the ability to influence people or events
** Abusive power
Power may a ...
throughout the entire time it is accelerating. E.g. in a truck with a Caterpillar C15 engine it is achieved by going all the way up to 1950RPM, then shifting to a gear that will put the engine at 1500RPM.
In contrast, using progressive shifting, i.e. maintaining maximum
torque
In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of th ...
, the overall acceleration is slower but there is increased
fuel efficiency
Fuel efficiency is a form of thermal efficiency, meaning the ratio of effort to result of a process that converts chemical potential energy contained in a carrier (fuel) into kinetic energy or work. Overall fuel efficiency may vary per device, wh ...
and lower wear of engine due to smaller RPM.
External links
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*{{cbignore
Trucks