What does overdrive mean? Automatic gearbox

BlackWizard

I got a new car last week. It's a Nissan X-trail and it has an automatic gearbox. But there is a button on the gear stick which is for turning overdrive on and off. I read it's like a final gear for cruising on the motor way.

Just wondering how I should use overdrive? It's always on. When I press the button it comes up on the dash that it's turned off.

I get the impression that I should leave it on all the time as the light looks like a warning light when I turn it off. But I'm not sure if I should be using it if I'm not on the motorway or if it would affect my fuel consumption.

colm_mcm

I only ever use it when overtaking on the open road. it's handier than wating for the gearbox to kick down.

Leave it (overdrive) on (as in light off) as you don't need it most of the time.

Anan1

The manual will explain, but i'd imagine it locks out top gear. It's only likely to be useful when towing or descending steep hills.

BlackWizard

colm_mcm wrote: »

I only ever use it when overtaking on the open road. it's handier than wating for the gearbox to kick down.

Ah okay. So you would turn overdrive off in my car to help with overtaking?

So it's okay for be to be doing lots of city driving with overdrive left on?

BlackWizard

Anan1 wrote: »

The manual will explain, but i'd imagine it locks out top gear. It's only likely to be useful when towing or descending steep hills.

The manual is pretty bad. It just says it turns overdrive off and on again. But it does mention it can be used for steep inclines when engine braking is needed.

Quazzie

Overdrive is an old reference to gear ratios. Most gears in a car have a gear ratio of less than 1:1 where as the overdrive was the top gear and was usually over 1:1 and was generally used for top speed motorway driving where acceleration and torque wasn't neccesary. Considering yours on a jeep I'd imagine that the overdrive should be turned off when towing, or when acceleration of high levels of torque are needed. I could be wrong on that though.

Anan1

Quazzie wrote: »

Overdrive is an old reference to gear ratios. Most gears in a car have a gear ratio of less than 1:1 where as the overdrive was the top gear and was usually over 1:1 and was generally used for top speed motorway driving where acceleration and torque wasn't neccesary. Considering yours on a jeep I'd imagine that the overdrive should be turned off when towing, or when acceleration of high levels of torque are needed. I could be wrong on that though.

That's pretty much my understanding too. Basically use it whenever you have a good reason for not wanting the car to use top gear (ie probably almost never).

JHMEG

Overdrive increases the output speed of the engine via gearing, before it's input into the transmission.

Overdrive enabled increases fuel economy by allowing the engine to spin slower at a given vehicle speed. By the same merit it decreases the torque multiplication effect meaing the car will have less poke with overdrive enabled.

I haven't seen an overdrive button in a long time. On most autos it's integrated into the gearbox and is controlled by the ECU.

Anan1

I had a 1990 Maxima with one, it just locked out top gear. Mind you, the same job could be done by just putting the transmission in '3'.

Quazzie

JHMEG wrote: »

Overdrive increases the output speed of the engine via gearing, before it's input into on its output from the transmission.

Overdrive enabled increases fuel economy by allowing the engine to spin slower at a given vehicle speed increasing the output speed of the transmission relative to the engine, thus resulting in the engine requiring less RPM. By the same merit it decreases the torque multiplication effect meaing the car will have less poke with overdrive enabled.

I haven't seen an overdrive button in a long time. On most autos it's integrated into the gearbox and is controlled by the ECU.

Fixed a few things in your post

colm_mcm

they don't always just lock out the top gear. My neighbour has a Corona (Carina E) import, it's a 4 speed plus overdrive, and overdrive isn't the same as 3dr gear on that car.

As others have said, tiptronic style boxes are becoming the norm now and overdrive buttons are all but gone.

CJhaughey

I remember 5th gear being called Overdrive on a manual gearbox.
Just a high ratio gear that would allow the engine to run at lower revs at cruising speed than a normal 5spd 'box saving fuel.

SouperComputer

The overdrive switch is used to turn off overdrive in situations were your driving situation causes it to pop in and out of O\D. An example would be where your speed is varying from 30-40mph and you often have to accelerate to 40, then back down to 30, yadda yadda. Rather than it popping in and out of O\D, it will just hold the next gear down, provided that gear is in range. It's rare that you will have to use it. Ive probably used it three times in as many years.

BlackWizard

okay thanks for the info guys. I just leave it be. I don't think I need to touch it then.