[n_aditya]

most economical driving speed foe me was a steady 80kmph on the highway in my esteem. The a/c was on and yet i got an FE of 19.xx kmpl.

One has to shift between 1.5k and 2k RPM and into 5th above 40kmph, (traffic conditions permitting) for getting good FE.

[vasudeva]

Originally Posted by tsk1979

Depending on the torque curve of the vehicle and also the coefficient of drag(cg) your best mileage speed will vary.

Of course, you are more knowledgable on this. Support for this is provided below from OECD's 2004 document `Can Cars come Clean'.

When a vehicle is moving, several resisting forces must be overcome. Resisting forces that arise from the interaction between the vehicle, the air and the road are:
Aerodynamic drag, which depends on the shape of the vehicle and the frontal area and is proportional to the square of the speed.
Rolling resistance, which depends on the tyres, tyre pressure and on the quality of road and is proportional to the weight of the vehicle.
Resisting forces related to the weight of the vehicle:
Inertia during acceleration, which depends on the weight of the vehicle, but also on all the rotating pieces (wheels, components of the engine and of the gearbox).
Gravity along a slope.

These forces are a function of the use of the vehicle and can vary considerably. At high speed, the aerodynamic resistance is preponderant (more than 75% of the total), while in urban use the inertia resistance is more than 95% of the total. As well, the absolute values of the forces differ significantly from model to model. An indication of the power required to overcome the above forces was provided in a table (which I am not able to reproduce here). The table refers to a passenger car of 1100 kg with a frontal area of 1.75m2 and an air resistance coefficient of 0.45. The figures indicate that for urban use the weight of the vehicle is a very important determinant of the power requirements (and the fuel consumption) for passenger cars. This is also the case for delivery vans and buses. Also that Power (kW) required to overcome various forms of resistance to forward movement of the vehicle is lowest at 4.9 KW for 60 kmph, horizontal (no gradient or slope); and highest at 39.5 KW for 140 kmph, horizontal. At 20 kmph urban speed, no gradient; power required is around 16.7 KW. The high power required at 140 vs. 60 is because of high power required to overcome rolling and aerodynamic resistance. Aero. resistance power required is 2.4 KW at 60 kmph, but 30.9 KW at 140 kmph. Rolling resistance power required is 2.5 KW at 60 kmph, but 9.4 KW at 140 kmph.

Even at constant speed, the power required to move a vehicle is dependent on the vehicle’s weight and aerodynamic drag. Power/energy/fuel required for a vehicle increases with weight, frontal area, and coefficient of drag (CD). The problem is that even with CD equal between 2 cars, higher frontal area can negate the advances made in reducing CD. On new passenger cars all around the world the frontal area of vehicles is increasing. So even with large improvements in the efficiency of engines, the potential gain in fuel consumption is being partly dissipated in practice.

[gigatech2006]

Originally Posted by vasudeva

Perhaps this link will help. There is a widely accepted graph (used by EPA, OECD, and IEA) which gives fuel economy at various speeds. The graph is in miles and to convert into km, multiply by 1.609344.

Tips to improve your Gas Mileage

Hmm..looks my Accent 'behaves' as per the figure that I observed in my previous post so..60 mph is 96 kmph..and my Accent gives a lil more than 17 kmpl at 95 kmph!

[Xehaust]

Originally Posted by adya33

2700 RPM
Hang on a second Astra not fuel efficient?
I used to get regularly 10 kmpl in Pune city with occasional AC and no I didn't do anything special to get better FE. Just regular driving.

Thanks for the Torque reading.
Just realised that i guess my oil had not been changed. Now im getting 7 & above in city driving with short distances and cold starts. Not to mention revving all the way to the red line once in a while on long drives. But them again, my driving style is also suited to getting as much as possible like anticipating braking and light on accelerator etc. while normal driving. Also my A/C is 85% of the time OFF.

Thank you Vasudeva for sharing the article.

[teknophobia]

The most economical speed on a diesel car is achieved at the highest gear with just enough pressure on the pedal to supply fuel to the engine. Diesel cars usually have the low end torque to keep the car moving at idle rpms

[GTO]

Originally Posted by teknophobia

The most economical speed on a diesel car is achieved at the highest gear with just enough pressure on the pedal to supply fuel to the engine.

Not true with modern diesels whose turbo kicks in at 1800+ rpm. Your suggestion would mean restricting the engine to 1500 - 1600 rpms, whereas a higher rpm with the turbo blowing would work out more fuel efficient.

[gemithomas]

Originally Posted by GTO

Not true with modern diesels whose turbo kicks in at 1800+ rpm. Your suggestion would mean restricting the engine to 1500 - 1600 rpms, whereas a higher rpm with the turbo blowing would work out more fuel efficient.

Would it be possible that mileage drops if you drive sedately (around 1500 rpm) and not letting the turbo kick at around 1800? I mean is it just the opposite than petrols where you tend to get better F.E running at lower rpms

[madhukar_n]

i doubt if we drive at 95 kmph.. the mileage is more.
i have seen if my average speed is about 80 or less, the mileage is more on highways. and most probably that will the case as on indian roads it is difficult to maintain a average speed of 100 or more.

[badboyscad]

My 2003 non-crde scorpio returns 11.5 to 11.9 kmpl when driven at 80 to 100kmph on highways(with a/c on).

[rider60]

The Best i Ever Got My Accent Viva was 23.2KMs per Liter of Diesel

well the Drive was on Stock tyres, completely stock car with minimal Luggage, with only me aboard, to Bangalore. It was Night Driving.

It Took me 14 Hours to reach Driving at 60Kmph-70kmph in fifth Gear!

Believe it or not drive this car in 80-90Kmph with relaxed acceleration i mean Sedate driving, the car will return 20+KMPL.

[Akshay1234]

got 16kmpl+ in my innova when my dad was driving it at 90-100kmph. it was a bombay-pune trip. of course that was the only time we actually finished almost a full tank on the highway otherwise no clue what it gives on highways.

i guess just a few 100 rpm above from which the turbo starts would be most efficient.

[tsk1979]

Once I had to drive safari around 50-60kmph for 300kms due to thick fog. I was in 4th gear and doing around 1700rpm.
The mileage I got... 17kmpl

[mobike008]

Originally Posted by rider60

The Best i Ever Got My Accent Viva was 23.2KMs per Liter of Diesel

I have to give it to you. You have loads of patience and amazing to see the maximum FE you could extract out of your Viva.

My Viva's best ever FE was during the first year and it was 20kmpl with the same sedate style of driving as you described. I could never get beyond 20kmpl ever after that one instance.

[rider60]

Originally Posted by mobike008

I have to give it to you. You have loads of patience and amazing to see the maximum FE you could extract out of your Viva.

My Viva's best ever FE was during the first year and it was 20kmpl with the same sedate style of driving as you described. I could never get beyond 20kmpl ever after that one instance.

thanks mobike,

well the patience part mate aah that was because i had to kill time as i started early at 4pm in the evening from the city to bangalore had to reach only the next day around 11 am not earlier due to some blah blah reasons, so that happened that one time.

Even more amazing is the figures Hyundai claims is after all very true for our beasts kudos to that mate. the claimed figure is 24.5KMPL

the figure i got driving it at 60 - 70kmph returned only almost only 1 kmpl less, AND Please note I was not doing the driving in STD Test conditions either. May be just May be if had the patience to drive the beast a little lesser 55-65kmph on that day it would have touched 24KMPL huh say what???

hE HE ha ha !

[sarinkumar]

Hi,
I got 14Km/litre from my SX4 ZXi during my recent visit to Palani. I was making sure not to cross 100Km/hr speed and was using A/C all along. Maruti claims that SX4 can give 15Km/litre. I think this speed looks like reasonable as the mileage is close to what the book says and also the car is totally under control at this speed.