What Is Overdrive?

Status
Not open for further replies.

Daniel

Well-Known Member
Joined
Sep 25, 2004
Messages
2,336
Location
Stavanger - Norway
A friend of mine took me out in his grandma's Toyota Camry '86 Auto wich had an Overdrive button on the leaver.

I know it has something to do with slippy grounds and that it was popular duringthe 80's. SO what exactly does it do?
 
Joined
Dec 9, 2003
Messages
4,905
Location
Decorah, IA
Car(s)
2004 Subaru Impreza WRX STI (USDM)
Not sure if the button does the same, but I believe overdrive is a gear ratio below 1.
 

Jostyrostelli

Forum Addict
Joined
May 29, 2004
Messages
8,061
I think it was only used for less fuel consumption. It's a gear in which the engine revs very slowly and the engine cannot give the wheels any more power.
If you know about ratios. The first gear : engine revs faster then the wheels.
Usually the 4th gear is the one where engine and wheels turn at the same speed. With 4th gear of Overdrive there is another "gear" where the engine runs slower then the wheels...I think others have a better explaination for it..
 

andyhui01

Forum Addict
Joined
Jun 4, 2004
Messages
8,532
Location
Melbourne, Australia
Car(s)
00' Subaru Forester GT
overdrive is only used in 4 speed gear-boxes and mainly on Mitsu. and toyota gearboxes... when the overdrive is turned off... the computer will automatically switch off the 4th gear... its good to use on highway when overtaking cars... tap the button and then accelerate... I also use that as engine braking on the highway as well :wink:
 

idletask

Active Member
Joined
Jun 25, 2004
Messages
256
Location
France
Overdrives were (yes, it's safe to say "were" here, only antiquated automatic slushboxes still have one) planetary gearsets that were found between the gearbox and transmission axle. It provided a direct link (off) or a surmultiplied link (on).

As a result you could get what normally now stands for a 5th gear. Some gearboxes even allows overdrives to work on other gears than the top gear, that could be very funny :mrgreen:

Basically, overdrives are the past now. With one planetary gearset alone anyway you can have four gears AND reverse depending on the acting/reacting component, so...

Oh, and read this well: as the overdrive was after the gearbox it had to support the torque at the output of the gearbox, not the engine! That's sometimes confusing because for example the Haldex system brochure says it can stand up to 2500 Nm of torque... Well, yes, but that's 2500 Nm out of the gearbox. As a result, it couldn't be fitted to, say, a 330d because in first gear max torque out of the gearbox is more than 4000 Nm...
 

idletask

Active Member
Joined
Jun 25, 2004
Messages
256
Location
France
Illustration...



(that's a Triumph Spitfire gearbox+overdrive assembly - yes, even on manual this could be adapted, but then you had to engage it by another lever)
 

Jostyrostelli

Forum Addict
Joined
May 29, 2004
Messages
8,061
No not sure, I once read it had a 6-speed semi-auto gearbox, but I have to look at the TG ep again..
 

joemoefro

Active Member
Joined
Dec 12, 2004
Messages
189
Location
Palo Alto, CA USA
I know with the Triumph TR6, you could have a theortical 10 forward drive gears. Because overdrive could be selected with every gear. This is a manual BTW. Pretty cool tranny if you ask me
 

bone

"bangle for president"
DONOR
Joined
Jan 14, 2004
Messages
16,442
Location
belgium!!
Car(s)
Volvo V40 & Yamaha Banshee
^just curious, why do you have the belgian flag in your avator????
 

andyhui01

Forum Addict
Joined
Jun 4, 2004
Messages
8,532
Location
Melbourne, Australia
Car(s)
00' Subaru Forester GT
zyran said:
Is there anything wrong with just leaving overdrive on?
I think you mean overdrive off... its better to leave the overdrive off when doing city driving and only turn it on when you hit the highway... I heard it saves some gas
 

Cubits

Active Member
Joined
Dec 7, 2004
Messages
149
Location
Brisbane, Australia
Car(s)
Peugeot 205 GTI Mi16 + JDM supercharged MR2
An overdrive isn't a gear less than 1, because you also have to factor in the other gearing components like the end ratio and the wheel diameter.

Overdrive is a gear ratio that's longer than the peak output of the engine could make use of, ie, one that is so long it doesn't yield top speed. Because the engine turns over so slowly, it's more fuel efficient.

The holden/vauxhall monaro has an interstellar 6th gear that is purely for fuel economy (which isn't any good regardless). ;)
 

SiR_dude

Well-Known Member
Joined
Mar 5, 2004
Messages
3,639
Location
Somewhere in rural Ontario, Canada
Car(s)
2000 Civic SiR
I wish I had overdrive :( Or a 6th gear. I love my car, but if I'm in a hurry and I want to cruise at 140 down the highway, I'm revving at 5,000 RPM, and the fuel economy isn't that great. Overdrive would be a big help.
 

joemoefro

Active Member
Joined
Dec 12, 2004
Messages
189
Location
Palo Alto, CA USA
think you mean overdrive off... its better to leave the overdrive off when doing city driving and only turn it on when you hit the highway... I heard it saves some gas
It doesn't matter because with overdrive on it'l just try to select the lowest gear driving around. With overdrive off, you may save your brakes a little because it won't select overdrive gear. With my old mustang which is thankfully gone, it went to overdrive around 45mph.

^just curious, why do you have the belgian flag in your avator????
Because i'm Half Belgium. And Belgium rocks, and they have really good beer :D
 

andyhui01

Forum Addict
Joined
Jun 4, 2004
Messages
8,532
Location
Melbourne, Australia
Car(s)
00' Subaru Forester GT
Sir_dude said:
I want to cruise at 140 down the highway, I'm revving at 5,000 RPM
wow... thats pretty high... I can get to abt 165 on the 3rd gear :D ... If I cruise at 110 on 5th... I get pretty good fuel ecomomy... 65l tank and I get abt 370km (pretty good for a turbo car)
 
Joined
Dec 9, 2003
Messages
4,905
Location
Decorah, IA
Car(s)
2004 Subaru Impreza WRX STI (USDM)
IIRC, my 93 Firebird Formula could cruise at 70mph (~115kph) at ~1500rpm in 6th.
 
Status
Not open for further replies.
Top