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It may very well be just my imagination, but 3 months ago i decided i can do 30 miles per hour on 3rd gear and not shift to 4th. It didn't seam like the engine was under any extra stress or anything, it was doing 2400 rpm (an around 1850 on 4th). I'm driving a 2005 C4 so my on-board PC tells me how many miles more I can do with the fuel in the tank For the month I only ever used 3rd for 30 mph I did 350 miles, but every other month before, and the two after (that I was going all the way up to 4th gear) I've been getting solid 400 miles per full tank.

Hence the question from the title: Is there correlation between fuel efficiency and preferred gear at 30 miles per hour.

Some extra info: I live in the UK, and always, always, always have my speed limiter ON.

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See this answer. Although it is for a different question, the same answer applies here: BSFC – Zaid Feb 1 at 8:45
    
@Zaid I'll check it out, cheers! – Иво Недев Feb 1 at 8:56
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I'm not sure why this is getting voted for closure as a driving technique. This is specifically about fuel efficiency and not about how to drive a car. I'm voting to leave open. I would hope whomever would reconsider their votes as well. – Pᴀᴜʟsᴛᴇʀ2 Feb 1 at 18:03
up vote 4 down vote accepted

There are two schools of though on this subject, at least in the UK. For the sake of fuel efficiency you should drive in the highest gear that your engine sounds happy with. At 30MPH in a 5 or 6 speed manual car that will probably be 4th.

The other school of thought (for the sake of road safety) is that if you stay in 3rd gear you are more likely to notice when your speed creeps up as the engine will be louder.

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The first school is correct - lower RPM at a higher gear (speed) will give you better mileage, as you cover a larger distance with the same amount of fuel injected. Except if the RPM is so low that your engine starts lugging, this causes bad things to happen. – I have no idea what I'm doing Feb 1 at 8:52
    
It starts lugging uder 11 mph, and my engine is very quiet. Following the first idea, i might as well do 5th gear, as the car would still move quite nicely, but then acceleration would be horrible for city commute... – Иво Недев Feb 1 at 8:56

As mentioned by @Sam people have two different driving habits. The important point when the higher gear is required and vice versa.


When you are driving in a highway or in the place where there is no need for any frequent change in speed you can go on higher gear with average speed is advisable. Kindly make sure to maintain the RPM not less than 1500 to avoid the damages to the engine /transmission /clutch.


When you are driving in the city or in the traffic area, you need to drive in low gear in the same time do not exceed 2500rpm. If you exceed 2500rpm the engine will be overheated and consume more fuel.


Hope this may help you to save fuel.

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Overheated above 2500rpm? – I have no idea what I'm doing Feb 1 at 10:51
    
Not exactly in all the vehicles, it is applicable for the vehicle with lesser rpm – Shameerariff Feb 1 at 11:26
    
Could you provide any references to what you are suggesting? – Pᴀᴜʟsᴛᴇʀ2 Feb 1 at 12:01
    
Shameerariff - your 3rd statement is factually incorrect. I drive my car almost exclusively between 3500 and 6000 rpm on my daily commute. Overheating is never going to be a problem. Also, your 2nd statement is incorrect. Low rpm will don't damage your clutch at all, and many cars are designed to happily run at lower than 1500. Can you edit your post and base it on actual evidence... – Rory Alsop Feb 1 at 12:35
    
@RoryAlsop I am used to diesel driven vehicle(Skoda Fabia) so on my experience, when it comes to the gasoline driven vehicle the rpm can go to the maximum as you said 6000rpm. But for the better fuel efficiency either it is diesel or gasoline engine never exceed 3500rpm unless it is really needed, I mean 80-100Kmph. When it comes to the lower rpm the user will not feel the pain of the engine, even at 1200rpm your car engine will go smoothly but the pulling power in your engine will go low, I mean when you are hitting a speed breaker or a sharp turn the engine will stall. – Shameerariff Feb 1 at 13:28

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