The Often-Mistaken Function of the ‘Overdrive’ Button in Auto Cars

Image: 2jsautomotive.com

One interesting aspect of driving an automatic transmission car is that there are just too many buttons and functions that were not learned in driving schools.

Most Singaporeans would have bought a second-hand car that has no instruction manual (i.e. if we even read it), so it’s not uncommon for us to ignore the additional functions.

A good example would be the L gear—anyone knows what it does? Most people in my office have a driving license, yet none of them know what the L gear does. One even jokes that it’s for “Learning”.

If you’ve a car with an automatic transmission, you would also realize that there’s an “Overdrive” button. For older Toyota models, it’s located on the gear stick, just below the unlock button.

OD1
Image: my-techie-guy.blogspot.com

Some cars might have the button elsewhere (sometimes a little hidden) but it’ll always be there. The default setting will not show anything on your dashboard, but if you press it, you’ll see this.

Image: my-techie-guy.blogspot.com
Image: my-techie-guy.blogspot.com

So, that means Overdrive is “On” by default. What exactly does this do then? I’ve got to admit that when I first saw it, I thought it means I could floor the pedal and increase the RPM without changing the gear, so it allows me to speed up fast.

Overdrive mah, over the driving limit mah?

Well, I was totally wrong. To understand how this works, we need to know how to drive a manual transmission car. In such a car, there will often be five gears: Gear 1 will be most powerful but could not go fast, and Gear 5 will be least powerful but could go fast. As we drive, we would usually be at Gear 3 or 4 on minor roads, and Gear 5 on expressways.

Overdrive: What it really is

An automatic transmission car does have gears as well, and they will change the gears depending on your speed. If your overdrive is on, you’ll slowly progress to the highest gear so as to cruise. Overdrive is essentially Gear 4 or 5: i.e., when you’re cruising at a constant speed without the need to speed up abruptly.

Now, if you switch it off, you will not go beyond Gear 4 or 5—because overdrive is off. Just think of it this way: you’ll be driving at 90 kmh in Gear 3. It’s going to be loud and your car will be drinking petrol like water.

Then why people turn off overdrive?

In Singapore, it’s almost never necessary to turn it off: our roads are pretty flat, so as we cruise, we do not need extra power to maintain our speed. However, in certain countries, there might be a long, steep road, and having the gear automatically going to overdrive gears would not be advisable since you need power to push the car up the slope.

Sometimes, if the car has got lots of load, or if it is towing another car, overdrive might need to be turned off since it needs more power to push the car. But hey, in Singapore, you won’t have an overloaded car nor a car towing a car!

(Article continues below) Most Touching Singapore Video: Jenny is brought up by a single parent, and when she steps into adulthood, she starts to forget that her mother used to be her everything. Watch it here:

(Since you’re here, subscribe to our YouTube Channel for more informative videos lah)

So, we should never turn it off?

If you can think of a reason to turn it off, go ahead. But looking at the function of it, keep it on unless you intend to drive to Genting Highlands.