What does Overdrive do ?

[PsychoChimp22]

Matra has it right, anything holding gears longer would usually just be called sport mode or something like that. That's certainly what Volvos do. But yea, with the 5 and 6 speed autos around now, and especially with CVTs, overdrive is unnecessary.

Look man, i know for a FACT that atleast in teh case of a 1995 Mercury Villager that overdrive means and does exactly what it does, its the exact same on my dads jeep aswell.

[taz_rocks_miami]

Don't any of you know anything about cars??? When you put the car into overdrive...........................









............................it goes a gazzzilion miles per hour!!!!!

[Matra et Alpine]

Look man, i know for a FACT that atleast in teh case of a 1995 Mercury Villager that overdrive means and does exactly what it does, its the exact same on my dads jeep aswell.

Go get the owners manual.

It is either an Overdrive and it has an extra post-gearbox gear.
OR it is NOT an Overdrive.

The manual will amke it clear to you.

"Overdrive" does NOT mean it will "over drive the gears".

[drakkie]

Don't any of you know anything about cars??? When you put the car into overdrive...........................

...........................it goes a gazzzilion miles per hour!!!!!

but only after accelarating very slowly.i witnessed this first hand, as a my friends uncle tried to keep up with an Audi in his Hyundai Elantra automatic i think he reached something like 175 km after a very,very,very long time of kicking the pedal through the bottom by that time, the Audi was long gone ...

Offcourse this all didn't happen in Germany but in the Netherlands where there IS a speed limit of 120

[culver]

I’m going to partly disagree with Matra on this one. Overdrive, like many other automotive terms is used to describe several different things. It may not be the technical definition but by virtue of common use it is a definition.

One way the word is used is to describe any sets of gears in a transmission (auto or manual) that result in the output spinning faster than the input. For example, in many 5spd manual transmission (such as the Miata/MX-5) 4th gear is basically a pass through with a ratio of 1:1. 5th gear actually increases the output shaft relative to the input shaft (0.78:1 I think). On older VW transmissions this was labeled as E or Economy rather than 5th. A few cars like GM’s 6spd F-Body cars and the Corvette have a double overdrive. 5th is something like 0.75:1 and 6th is a very long 0.50:1 (Got to love that torque).

On an automatic is used to refer to an add-on module that would turn your three speed transmission into a 4 speed box. 3rd would likely be a 1:1 and 4th would be less something less than that. As Matra said this was an add on unit to a three speed auto. This is probably why on many cars it was controlled by a separate button rather than just being integrated into the shifter detents. Actually, I think the early ‘80’s Corvettes had some weird 4spd manual with an automatic style overdrive module. I don’t remember how OD was selected. I don’t recall the boxes being well liked and they were eventually replaced with real 6spd boxes.

Now that basically all autos are at least 4speeds this function has been physically built into the transmission and is no longer a separate module. Though built into the box these gears function the same way and cause the box to have a ratio off less than 1:1. Many autos still have the ability to deselect top gear for things like towing or engine braking on long hills. Some of the early 5spd boxes were actually 4spd boxes with a software change that allowed the overdrive gear set to kick in when the main gear set (1st 2nd and 3rd gears) was in 2nd. Thus 2nd with overdrive became something higher than 2nd but less than 3rd.

So basically depending on context, overdrive can describe a gear ratio that is less than 0.X:1 or an external module that attaches to a gear box to reduce the final drive when engaged.

[targa]

HOOD and trunk.

no, those arent the same, the hood is the front, the trunk is the back

he said hood and bonnet, which are the same, but from the UK and USA respectivle

so i said boot and trunk, the boot being what they call our trunk over here

[h00t_h00t]

Hood is an American term, and Bonnet the British one.

[henk4]

I’m going to partly disagree with Matra on this one. Overdrive, like many other automotive terms is used to describe several different things. It may not be the technical definition but by virtue of common use it is a definition.

One way the word is used is to describe any sets of gears in a transmission (auto or manual) that result in the output spinning faster than the input. For example, in many 5spd manual transmission (such as the Miata/MX-5) 4th gear is basically a pass through with a ratio of 1:1. 5th gear actually increases the output shaft relative to the input shaft (0.78:1 I think). On older VW transmissions this was labeled as E or Economy rather than 5th. A few cars like GM’s 6spd F-Body cars and the Corvette have a double overdrive. 5th is something like 0.75:1 and 6th is a very long 0.50:1 (Got to love that torque).

On an automatic is used to refer to an add-on module that would turn your three speed transmission into a 4 speed box. 3rd would likely be a 1:1 and 4th would be less something less than that. As Matra said this was an add on unit to a three speed auto. This is probably why on many cars it was controlled by a separate button rather than just being integrated into the shifter detents. Actually, I think the early ‘80’s Corvettes had some weird 4spd manual with an automatic style overdrive module. I don’t remember how OD was selected. I don’t recall the boxes being well liked and they were eventually replaced with real 6spd boxes.

Now that basically all autos are at least 4speeds this function has been physically built into the transmission and is no longer a separate module. Though built into the box these gears function the same way and cause the box to have a ratio off less than 1:1. Many autos still have the ability to deselect top gear for things like towing or engine braking on long hills. Some of the early 5spd boxes were actually 4spd boxes with a software change that allowed the overdrive gear set to kick in when the main gear set (1st 2nd and 3rd gears) was in 2nd. Thus 2nd with overdrive became something higher than 2nd but less than 3rd.

So basically depending on context, overdrive can describe a gear ratio that is less than 0.X:1 or an external module that attaches to a gear box to reduce the final drive when engaged.

Sorry, the issue is not about the gear rations within the gearbox, these can be varied at will (depending on the torque of course). The classic overdrive as already described by Matra is a device outside the gearbox, used to further reduce the revs of the driveshaft in order to get a higher speed with the same engine revs. In MANUAL gearboxes you had to switch it on manually, and it was mostly only available on the fourth gear, but sometimes also on both third and fourth. The arrival of 5 and 6 speed manual boxes has made the use of an external overdrive redundant.
What goes on in autoboxes might result in lower than 1 final drives, but has nothing to do with the classic meaning of overdrive. Interestingly, my granddad's old Horch 853 had a reduction box (like a 4x4) which gave in theory 8 speeds in stead of 4. The highest gear was called "Schnellgang", ('fast speed") but was not an overdrive in the classic sense.

[2ndclasscitizen]

In the Tremec T-56 used by Holden, the 5th and 6th ratios are like 1 and 0.86, this another type of overdrive isn't it?, as this lets them rev at like 1500 on the highway. I thought the overdrive button has evolved into like power or sport buttons these days and mostly related to the gearbox holding the gears longer

[fpv_gtho]

I think thats what the SV6's 6 speed has, since its diff ratio is under 3:1. AFAIK, all T-56's have double overdrives, in the case of the ones Holden use in the V8's its something like 0.7 and 0.5, with 4th as 1:1.

[culver]

Sorry, the issue is not about the gear rations within the gearbox, these can be varied at will (depending on the torque of course). The classic overdrive as already described by Matra is a device outside the gearbox, used to further reduce the revs of the driveshaft in order to get a higher speed with the same engine revs. In MANUAL gearboxes you had to switch it on manually, and it was mostly only available on the fourth gear, but sometimes also on both third and fourth. The arrival of 5 and 6 speed manual boxes has made the use of an external overdrive redundant.
What goes on in autoboxes might result in lower than 1 final drives, but has nothing to do with the classic meaning of overdrive. Interestingly, my granddad's old Horch 853 had a reduction box (like a 4x4) which gave in theory 8 speeds in stead of 4. The highest gear was called "Schnellgang", ('fast speed") but was not an overdrive in the classic sense.

I agree with your classical definition of an overdrive unit and stated as much in my post. However, the term "overdrive", as apposed to an "overdrive module" is also, commonly used to refer to gear ratios less than 1:1. It may not be the classical definition but like many words the term has evolved and now can refer to gear ratios inside a box rather than just a module on the box. This makes sense as a 3 speed gear box would have third as a pass through 1:1 type gear. The overdrive module would reduce this output to something other than 1:1. When every car started coming with overdrive the automakers simply built that functionality into the box (4spd vs 3spd w/ overdrive). At that point the term shifted from strictly meaning an add on "overdrive module" to an internal to the gear box "overdrive." Hence the Corvette and Camaro coming with double overdrive 6 speed gearboxes. In reference to gear ratios less that 1:1 this term is commonly used by automotive writers. Perhaps the definition is also colors by "other side of the pond" type issues.

GM uses the overdrive term in reference to gear ratios, not add on modules:
http://media.gm.com/division/chevrol...ette/trans.htm

[henk4]

I agree with your classical definition of an overdrive unit and stated as much in my post. However, the term "overdrive", as apposed to an "overdrive module" is also, commonly used to refer to gear ratios less than 1:1. It may not be the classical definition but like many words the term has evolved and now can refer to gear ratios inside a box rather than just a module on the box. This makes sense as a 3 speed gear box would have third as a pass through 1:1 type gear. The overdrive module would reduce this output to something other than 1:1. When every car started coming with overdrive the automakers simply built that functionality into the box (4spd vs 3spd w/ overdrive). At that point the term shifted from strictly meaning an add on "overdrive module" to an internal to the gear box "overdrive." Hence the Corvette and Camaro coming with double overdrive 6 speed gearboxes. In reference to gear ratios less that 1:1 this term is commonly used by automotive writers. Perhaps the definition is also colors by "other side of the pond" type issues.

GM uses the overdrive term in reference to gear ratios, not add on modules:
http://media.gm.com/division/chevrol...ette/trans.htm

Automotive writers talk about: the highest gear(s) having the characteristics of an overdrive, but it still simply is a gear and nothing else. Anything less than 1 to 1 can literally be considered "overdrive" as the outgoing shaft from the gearbox runs faster than the incoming shaft from the engine. But I agree this is nitpicking, the classic add-on overdrive (the having of which many cars from the fifites and the sixties like Volvo or Triumph were proud to sport as a special badge on the rear of the car) has disappeared.

[Matra et Alpine]

The conclusion I've come to on this is that at some time in the US a marketing person decided that saying a car had "overdrive" was a plus in the days when it was real overdrive and came up with reasons to get away with calling what he was selling was "overdrive" rather than just saying it had a top gear of a given ration.

Sounds all hype, smoke and mirrors I'm afraid.

[aNOBLEman]

A TRUE overdrive as has been explained is an ADDITIONAL gearing on the output shaft of the gearbox which further increases the drive shaft speed for the same engine speed.

IT is NOT a "gear" in the gearbox. Those are called "gears"

The optoin for an automatic to delay the point where it automatically switches up a gear is NOT OVERDRIVE - even if at some point some noob nerd thought it did and the word has passed around. They're wrong An automatic box can decide for a variety of reason to shift up or down at different rev ranges. These are often in the user manual as "heavy load conditions".

So recap. OVERDRIVE is an EXTRA gear system in series with the gearbox as BjD explained in http://www.ultimatecarpage.com/forum...53&postcount=3

That's what I thought. Basically it gives you better gas mileage at highway speeds. The thing that makes shift points different and quicker is on large SUVs and trucks for towing. It makes the shifts at different rpm's so that the engine stays in the optimal power and torque curve.

[SonyAD]

An overdrive device is what Matra said.

An overdrive gear is any gear above that within which the vehicle is able to attain maximum designed speed (excluding electronic governors or speed limiters).

An overdrive gear is NOT a gear with a demultiplication ratio of less than 1:1, like a bazillion people dead wrongly believe and will happily 'educate' you.

THE VAST MAJORITY OF CARS DO NOT HAVE AN OVERDRIVE GEAR OR OVERDRIVE DEVICE.

It is amazing what little chance the truth usually has against misinformation and disinformation.