What Is Overdrive?

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chaos386

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If you have and older car with a not-quite-so-good automatic, it's sometimes a good idea to switch off the overdrive if the car can't choose between the top gear and the one below it. I had a Mercury Grand Marquis which would shift into top gear at 40mph, so sometimes I turned off overdrive when drving in 45mph speed zones. Any time else and you should leave it on to improve highway fuel economy.

As for manual overdrives, a friend of mine once drove a volvo stationwagon which had a four-speed manual with a button on the top to select fifth gear (overdrive). I never quite understood why until this thread. :lol:
 

Greatgraddage

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I have a friend who has overdrive fitted to an old series 2 land rover. It works in all gears including reverse! He say's he could get over 40 in reverse if he tried but he's too scared to try it!
 

smeghead

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Most cars these days run more gears rather than an antiquated overdrive system. If you look at most of the big German cars they have a very tall 5th or 6th gear so you can cruise along at 90mph at around 3,000rpm. My old 5 series had an overdrive system in it, and it would do 90mph at about 2,400rpm! It relies on engine torque to a much greater extent, but it does reduce engine revs, reducing your minimum level of fuel consumption, even thought more fuel will need to be used in each injection because of the higher torque requirement.

My old car would do 50mph in first gear, 80 in 2nd, and 110 in 3rd!!! Was quite crazy after my original Mini Cooper which could only manage 20mph in 1st!

Trouble with longer gear ratios is that they do kill acceleration a little, although reduced gear changes means less time lost performing them. Just means you can't give it full potatoes in more than 3 gears :( In the RS4 you can lose your liscence in 2nd gear in the UK!!!!

Sam
 

bone

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