Overdrive
Record Breaker
Joined: Dec 2005
Posts: 1,412
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From: Nashville
As Alloro stated in his posting about the OD to just let it stay has good merit. Even in areas that are suburban and not inner city, the OD is used from 38MPH and upward. If I would turn it off, the MPG will tank badly. So, unless there is a heavy load or towing, it stays on, even in the hills of TN and KY that I typically drive in.
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Joined: Nov 2013
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What is the consensus on using overdrive? Obviously Chrysler enabled overdrive by default, so they must have intended for it to be used normally on an every day basis? Personally, I never use overdrive unless I'm on the highway (which is not very often), but on a day-to-day basis, I manually shut it off every time I get in the truck.
Now, if someone were to run the van daily in stop and go traffic with overdrive on, would this shorten the life of the transmission? To me, overdrive is supposed to be an option to only use as needed, so why is it always enabled and why force people to disable it all the time?
Now, if someone were to run the van daily in stop and go traffic with overdrive on, would this shorten the life of the transmission? To me, overdrive is supposed to be an option to only use as needed, so why is it always enabled and why force people to disable it all the time?
Use of the term is confused, as it is applied to several different, but related, meanings The most fundamental meaning is that of an overall gear ratio between engine and wheels, such that the car is now over-geared and can no longer reach its potential top speed, i.e. the car could travel faster if it were in a lower gear, with the engine turning more quickly. In some cases this implies a second definition is also true, that the gearbox output driveshaft is rotating faster than the original engine RPM. This later definition was common in the past, but many cars no longer have a driveshaft and it is not technically correct.
In the era of front-engine, rear-wheel drive layouts, the device for achieving an overdrive transmission was usually a small separate http://en.wikipedia.org/wiki/Gearbox, attached to the rear of the main gearbox and controlled by its own shift lever or electrical actuation button. These were often an optional extra on some models of the same car. As popular cars became faster relative to legal limits and fuel costs became more important, particularly after the http://en.wikipedia.org/wiki/1973_oil_crisis, the use of 5-speed gearboxes became more common in mass-market cars, with the 5th gear being an overdrive, eliminating the need for a separate gearbox
With the popularity of http://en.wikipedia.org/wiki/Front_wheel_drive cars, the separate gearbox and final drive have merged into a single http://en.wikipedia.org/wiki/Transaxle. However the fundamental meaning, that of an overall ratio higher than the ratio for maximum speed, still applies. Although the deliberate labelling of an overdrive is now rare, the underlying feature is now found across all cars.
Last edited by Vanme; Nov 13, 2013 at 03:08 AM.
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Professional
Joined: Aug 2013
Posts: 132
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An overdrive (OD) is a mechanism that allows a car to cruise at sustained speed with reduced engine RPM, leading to better fuel economy, lower noise, and lower wear
Use of the term is confused, as it is applied to several different, but related, meanings The most fundamental meaning is that of an overall gear ratio between engine and wheels, such that the car is now over-geared and can no longer reach its potential top speed, i.e. the car could travel faster if it were in a lower gear, with the engine turning more quickly. In some cases this implies a second definition is also true, that the gearbox output driveshaft is rotating faster than the original engine RPM. This later definition was common in the past, but many cars no longer have a driveshaft and it is not technically correct.
In the era of front-engine, rear-wheel drive layouts, the device for achieving an overdrive transmission was usually a small separate gearbox, attached to the rear of the main gearbox and controlled by its own shift lever or electrical actuation button. These were often an optional extra on some models of the same car. As popular cars became faster relative to legal limits and fuel costs became more important, particularly after the 1973 oil crisis, the use of 5-speed gearboxes became more common in mass-market cars, with the 5th gear being an overdrive, eliminating the need for a separate gearbox
With the popularity of front wheel drive cars, the separate gearbox and final drive have merged into a single transaxle. However the fundamental meaning, that of an overall ratio higher than the ratio for maximum speed, still applies. Although the deliberate labelling of an overdrive is now rare, the underlying feature is now found across all cars.
Use of the term is confused, as it is applied to several different, but related, meanings The most fundamental meaning is that of an overall gear ratio between engine and wheels, such that the car is now over-geared and can no longer reach its potential top speed, i.e. the car could travel faster if it were in a lower gear, with the engine turning more quickly. In some cases this implies a second definition is also true, that the gearbox output driveshaft is rotating faster than the original engine RPM. This later definition was common in the past, but many cars no longer have a driveshaft and it is not technically correct.
In the era of front-engine, rear-wheel drive layouts, the device for achieving an overdrive transmission was usually a small separate gearbox, attached to the rear of the main gearbox and controlled by its own shift lever or electrical actuation button. These were often an optional extra on some models of the same car. As popular cars became faster relative to legal limits and fuel costs became more important, particularly after the 1973 oil crisis, the use of 5-speed gearboxes became more common in mass-market cars, with the 5th gear being an overdrive, eliminating the need for a separate gearbox
With the popularity of front wheel drive cars, the separate gearbox and final drive have merged into a single transaxle. However the fundamental meaning, that of an overall ratio higher than the ratio for maximum speed, still applies. Although the deliberate labelling of an overdrive is now rare, the underlying feature is now found across all cars.
