Tech Thursday: OverDrive
If you’re like me, you know that your car has overdrive, because there’s a button for it, and you have a general idea of what it does, but you’re not really sure you could explain it to someone else. For this week’s Technology Thursday, I offer a quick-and-dirty explanation of overdrive, as it’s commonly used.
Basically, overdrive (aka OD) is the highest gear in your transmission. Automatic transmissions have three speeds plus overdrive, which allows the engine to use a lower rpm than “normal� for any given road speed, which in turn offers better fuel efficiency, and sometimes quieter driving on highways.
When overdrive is switched on, it allows the engine to move into OD mode after a specific speed threshold is met (usually around 45 mph), and when it is off, the lower gears are the only options available. Generally speaking, it should only be used in normal driving conditions when you’re driving faster than 45 mph.
While overdrive is on, the transmission will automatically move into third gear when there is more load, and back to OD when there is less. For this reason, driving up steep grades, or towing a trailer can cause the transmission to shift back and forth between third and OD, as if “huntingâ€? for the right place. In these cases, and if you need to use the brakes frequently (like when you’re driving downhill), it’s best to turn overdrive off.
August 23rd, 2007 at 3:39 pm
A good rule of thumb is to switch off overdrive going up hills that have an additional lane. ie. mountain roads often give a passing lane for the up hill side, in which case gear down and you’ll not stutter up the mountain.