Overdrive and what you should know about it

Thursday August 15 2019

You should leave the OD switch on all the time

You should leave the OD switch on all the time for regular driving. Your car will automatically shift into top gear if necessary, regardless of your selection. Photo by Isaac Ssejjombwe 

By Roland D. Nasasira

When you look closely at the gear lever in your car, especially those with automatic transmission, you will see initials O/D engraved on its side. In some vehicles, the two words are written in full. These initials stand for overdrive. In vehicles such as the Toyota Ipsum and Toyota Vista, whose gear lever is next to the steering wheel, the overdrive button is on the edge or tip of the lever.

How overdrive works
While few motorists such as Anne Kusiima have never really understood how and where overdrive is applicable, others such as Francis Twijukye, say they press the overdrive button to activate it along highways when overtaking. He is, however, cautious and only overtakes with overdrive when there are no vehicles from the oncoming direction which, if not carefully observed, can cause head-on collisions.
“When I engage overdrive, the car engine gains more firepower and shifts to the highest gear to allow fast overtaking,” he says.
“When I am speeding and I see something ahead that requires me to control the car, I press the overdrive button to shift to a lower gear. This allows me to control the vehicle firmly instead of braking where there are high chances of overturning because of speeding,” Twijukye adds.

What is overdrive?
According to mechanicbase, an online portal, overdrive is a special gear that reduces the burden on an engine. In simpler words, it configures the engine to perform optimally according to the current requirements. An engine creates more power in lower gears where the gear ratio lies above one. “In overdrive, the gear ratio is between 0.6 to 0.8 against one. This allows the car to speed but in a low revolutions per minute. In essence, the overdrive gear focuses more on producing faster wheel rotations in a minute instead of making more torque for acceleration,” the portal explains.
When to use overdrive
Isaac Mujjawa, a mechanic, says much as overdrive enables a car to move faster, it is good to activate it when driving slowly, especially in urban areas such as Kampala with slow moving traffic. It should be used when you are speeding, most notably above 60km/hour.
“When you turn on overdrive, the revolutions per minute produced by your engine significantly reduce. Fuel consumption also reduces significantly and your car will be faster. This is the reason your engine will consume more fuel in urban areas and marrum roads where you drive slowly compared to a highway where the vehicle is fast and uses less fuel,” Mujjawa notes.

Overuse danger
Overdrive allows you to save fuel but this does not mean that you use unnecessarily. The downside of overdrive misuse is that you will lose control of the car, all in the name of saving fuel.

Overdrive in manual cars
However, overdrive is only applied in automatic cars. This is because in cars with manual transmissions, the highest gear, which is in most cases five for saloon and sport utility cars and rarely six, is the highest gear with which you can drive the fastest.
In simple terms, gear five or six or the highest gear in your manual transmission car is where and when overdrive is applicable.