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what is the recommended driving speed for a petrol car with manual transmission to have maximum fuel efficiency?

in India AFAIK it is 60 Kmph

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up vote 3 down vote accepted

It's hard to say as it depends on various conditions like the gearing of your car but on a perfectly flat road, I'd say put the car into the highest gear and take your foot off the throttle. The speed the car settles down to is just about your most efficient cruising speed: Highest gear, no throttle.

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If you do this engine braking will slow the car until it the engine reaches idle speed and then the ECU will adjust the idle air control valve to maintain idle speed, unless it's an old car with carbs in which case it'll stall. The last time I tried this I wound up at about 25mph. BUT, this is not necessarily the most efficient speed as car engines are not very efficient at idle speed. – squigbobble Jan 7 at 17:31

There is no 'per-country' recommended driving speed for fuel efficiency.

It depends on the shape of your car, your engine size and type, the type of fuel you use, the quality of the roads etc.

In my car for example, in top gear I can get 37 mpg at 60mph and it has a gentle drop up to about 75mph, but the efficiency drops off rapidly over 75mph (35mpg at 75 down to 22mpg at 90mph, and dropping further as I get faster) so I tend to use 70 as my general target despite getting slightly better efficiency at a lower speed.

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Remember that atmospheric drag increases with the square of the velocity (and that's BEST case). – Bob Cross Oct 1 '12 at 22:05

The "best fuel economy values" range (according to tests I've read) from 40-55mph depending on the vehicle and conditions.

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so again that comes out around 65-70 kmph.. – Rishi Kalia Oct 2 '12 at 6:34
This is very vehicle dependent, since atmospheric drag is severely dependent on shape and velocity. A motorbike, car, and big truck will all have significantly different ranges. – Leliel Jul 8 '15 at 4:36

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