My little Scion wagon with automatic transmission has a button that toggles the overdrive on and off. In other words, the highest gear(s) that have the engine turning slower than the tires can be disabled.
Other than thinking it would be cool to drive along sounding like a vacuum cleaner, why should I want this?
One reason I don’t want it is they put the button where my knee keeps bumping it and turning it on. Is this just a completely stupid feature or is there a use for it?
Am I supposed to reach down with a manly hand while starting to drive around a bend, especially with shiny rain-slicked pavement at night, and do something with this? You know, like in the commercials?
You’d want to use it to downshift to get more engine braking on a long downhill grade. Also sometimes you get problems with the transmission “hunting” between the top and next-to-top gears when you’re going up a hill, so disabling overdrive will force the transmission to make up its damn mind already.
If you live in a mountainous area, the transmission can end up doing a lot of gear hunting going in and out of overdrive as you go up and down hills. If you notice the car shifting all wonky on hilly terrain like that, it’s best to turn the OD off.
Other than that, I’ve never seen much of a need for it.
Some folks say to turn it off when you are just driving around town, but I’ve personally never seen any need for that on any of the cars that I’ve owned.
Short version: one of the porpoises is to prevent the tranny from hunting for gears in hilly driving; another is to minimize torque converter lock up in stop and go.
How old is your car? I can’t remember the last time a car actually had an overdrive button… Overdrive is not a “stupid feature” and all modern cars have this, although it’s electronic now instead of a mechanical unit with a button.
Basically, what it does is allow you to drive at lower RPMs at certain speeds. Lower RPMs mean better fuel efficiency, a quieter engine, and less stress. Default position should be ON. Turn it off when you want to keep to lower gears such as when you’re towing, in stop-and-go traffic, or you want quick acceleration to pass somebody. Up-and-down hills will also confuse the automatic transmission to hunt for the right gear so it’s suggested to turn it off then.
Interesting. I was told that the reason was that driving in the city the transmission would be hunting out the overdrive gear unnecessarily as you changed speeds quite often.
Turning off the overdrive in the city vastly reduces the number of gear changes and therefore increases your transmission life.
I drive over a mountain pass every work day, about 1700 vertical feet. I use the overdrive button twice a day, once each direction. Little Hyundai Accent works just fine once you get the revs up.
This doesn’t make sense to me–overdrive won’t kick in until you get to higher speeds. I do a fair amount of city driving and it just never takes effect.
Depends on the car and what one thinks of as “city driving”.
On Manhattan, “city driving” means alternating between being stopped and going 20mph. In a lot of places, “city driving” is done in suburbia where the arteries have 40mph limits and 50-55mph speed of actual traffic.
One of our cars is a Jeep Liberty with a 4-speed auto + OD. 1st & second are real low, there’s a big gap up to third, then moderate gaps up to fourth and again up to OD. If driven gently on level ground, it’ll be in OD, turning 900 rpm, at 45mph. And will not accelerate worth shit from that condition. To drive that car on our arterial roads where you go from stoplight to 50mph then back to zero a mile later you really want to switch off OD. Otherwise at cruise speed it’s so luggy it’s dangerous; you have no ability to accelerate at all and the only way to change speeds is to brake.
Even my 2000 Saturn had enough programing to deal with gear hunting. And it also stayed in lower gear if I was going down hill and braked. It was actually a pretty good transmission.
Done in One.
Hunting is an issue with cruise control especially. Your car is trying to maintain a speed on a steep hill and overdrive does not have enough power, so the car slows, down shifts and aggressively re-accelerates to its former speed where it then shifts back into overdrive…Aaaaaaaaaaaaaand repeat. It will drive you crazy so you turn off overdrive and solve the problem, when you get to the top of the hill you start it back up.
Just to clarify, the overdrive itself - meaning just any gear in which the engine turns more slowly than the wheels - is a perfectly good feature if the wheel size, engine performance, and driving environment call for it. Though I have to suspect some sort of advertising foolishness in giving it a name, as there is nothing particularly important about a 1:1 ratio between engine and wheels.
What I was doubting is the need to be able to disable that gear. Likewise, I think third gear is perfectly useful, but don’t see why they’d give us a special button to disable it.
The hilly environment hunting thing sounds like reason enough. If I got to design things I might have put it on the side of the lever where my knee doesn’t switch it, but that’s getting pretty picky.
Well, these days the decision to have an “O/D off” button versus simply having an extra notch on the shifter is mostly an aesthetic decision since they’re all electronically controlled anyways.
Back in the 80’s and 90’s, though, some car makers did take hydraulically-controlled 3-speed transmissions and turn them into 4-speeds with the addition of an electrically-controlled overdrive gear. In that situation, it made sense that you had a button to lock out 4th gear but had to use the shifter to lock out 3rd and 2nd.
In car owners’ manuals, there’s “highway driving” and “city driving.” Since they’re going with a binary split, that actually parses as “uncongested high-speed highway driving” and “all other forms of driving”.
Which “all other forms” include congested highways, suburban residential, suburban arterial, twisty hilly rural, laser-straight Great Plains rural, dense inner city, etc., etc.
I think the reason is that if you are going at high speed, you definitely don’t want to grab the wrong selection, such as neutral, and like suddenly slow down in traffic. The slow down is especially dramatic if you are going up hill… With the switch, you are in the top gear or next to it…
I feel for the OP though, if their knee bumps the switch. As others have said, and at least IMHO it’s best used for mountain driving and towing. I drive over the continental divide at 11,500 feet every day. Twice. And I rarely use it in my Pathfinder. I will use it more in my Dodge truck if I’m towing something. :shrug: cars conditions and transmissions are all different. As are drivers.
For daily driving in basic conditions, just leave OD on. No need to monkey with it.
Two things that haven’t (quite) been mentioned are that most newer cars have several overdrive gears. “Overdrive” is any transmission setting where the output shaft turns faster than the input shaft. Older cars had the 1:1 gearing as the top gear, either 3rd or 4th. When 5-speeds came along, most of them were 1:1 on fourth, and a slight overdrive for fuel economy as 5th (typically around 0.85:1).
In the frantic bid for higher mileage, manufacturers have done two things: add more and more OD gears, and make them kick in at lower and lower relative speeds. Most cars these days have 3rd as the 1:1 gear, with either two or three OD gears above it, sometimes more. The lower the drivetrain controller can get engine RPM, the higher fuel economy goes, so some cars have a 6th (or higher) ID approaching 0.5:1. The more gently you drive, the quicker the tranny will ratchet up to the highest gear that keeps the car moving.
Cars with any slight sporting pretension will kick down out of OD quickly, but not quickly enough on hills or passing situations. So cutting out the OD locks the transmission in low-to-1:1 range, often giving MUCH better acceleration and accel response.
My Odyssey has a five-speed auto with dual OD and gets impressive mileage for such a big boxy vehicle. But on the long, low highway hills here, I rarely drive very far without hitting the “turbo button” to kick it out of OD so I can shoot past trucks and other obstructions. With OD on, when it’s cruising in 5th it takes a full two seconds or so from throttle-down to any noticeable acceleration; OD off, and it’s as jumpy as a sports car.
(Just to confuse things, my summer car has a 5-speed manual with no OD gearing - it’s a close-ratio box with a 1:1 fifth. I often drive in 3rd or 4th, leaving 5th for steady highway cruising.)
Just to re-clarify: It isn’t between the engine and wheels, it’s the ratio between the engine and drive shaft (or output shaft on the transmission) that is usually 1:1 in the highest ‘regular’ gear and higher than 1:1 (i.e. more turns of the output shaft per turns of the input shaft) in overdrive. The differential in RWD cars (it’s built into the transmission or ‘transaxle’ of FWD cars) not only distributes the power smoothly to both wheels, it also provides a final drive gear reduction between the output shaft and the drive axles (wheels).