Every car transmission has a sequential number of higher gears who that are designed to multiply the engines power so that the vehicle can attain a higher speed. Overdrive is designed to be an additional high gear ratio, to reduce engine RPMs and increase fuel economy when the vehicle is cruising. It’s a very handy feature and can certainly save money on road trips. But there are certain situations that a transmission overdrive setting is not appropriate. So let’s take a closer look at that now.
What Transmission Do I Have?
What is overdrive?
A car overdrive typically contains an additional planetary gear set up. If your car had say a six speed automatic, 5th gear would operate on a 1:1 ratio where the input shaft from engine would be turning at the same rate as the output shaft to the wheels. If overdrive is engaged, the wheels would be turning at a higher rate of speed than the engine RPMs. This would obviously save you fuel, and make a long-distance cruising lot more comfortable and quiet.
Why should you turn overdrive off
There is typically a button or switch labeled OD that allows you to turn the overdrive function on and off. This is actually very convenient because there are situations that you will want to disengage overdrive. For example, if you are driving up and down steep hills in a mountain type environment, then you’ll want to disengage overdrive. Your transmission will automatically seek out high gear/overdrive when it thinks you reach cruising speed, like when you’re coming down a steep hill. This will require you to use the brakes a lot more, and possibly overheat them. However if you turn the overdrive off, you get more engine braking when you’re coming down that hill and save your brakes.
What Transmission Do I Have?
Two more situations where overdrive might not come in handy are in heavy rain, because being in high gear won’t allow you to modulate your speed as quickly, which could lead to hydroplaning. Also, when you’re towing a heavy load and want to pass somebody, commanding the transmission out of high gear can help you get up to speed a lot more quickly.
