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Old 28th July 2007, 10:57   #1
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Cool most economical driving speed

"I know that the faster I drive my car, the more gas it uses. But on the other hand, I'll get to my destination in less time. Is there a "sweet spot" on the speedometer that would give me maximum fuel efficiency? And if so, is it different for different car models?" I got this queston from howstuffworks but I didn't get an answer. Obviously it depends on the aerodynamics, torque curves, among other variables, and this would be different for different vehicles. So I am asking you all BHPians for some inputs.
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Old 28th July 2007, 11:21   #2
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Hey Goandude,

Please search and look in threads with similar topics. I think this has been discussed several times.

If anyone can remember specific links, please do post em here and i will merge the threads.

cya
R

Last edited by Rehaan : 30th July 2007 at 03:27.
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Old 30th July 2007, 03:30   #3
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I dont remember where i read this, but :

I believe Maruti had once tested and the best way to get FE out of their 800 (? if i remember correct) was to drive at 40km/h in 4th.

As you said, it would defer from car to car based on torque curves, efficency, gearing, and as speeds get higher, aerodynamics would get exponentially important.

Hopefully someone else can chime in with more info.

cya
R
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Old 30th July 2007, 10:12   #4
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The carb esteem gives the best mileage when driven at 2000 rpm in 5th gear. Speed is 80kmph at that time.
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Old 30th July 2007, 10:18   #5
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When cruising, it is best to stick to a speed corresponding to the highest gear and the rpm being the maximum torque rpm.
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Old 30th July 2007, 11:05   #6
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As per my experience ideal speed for best FE is 50-60 kmph for every car with very less use of brakes and stick to proper rpm and never rip your car (I mean rpm around 2000 to 3000) hence less gear change.

Best FE achieved with this kind of driving :

2003 5 seator Omni -> 25kmpl
Santro Xing 2004 top end -> 24kmpl
Swift VXI 2006 -> 18kmpl.

Innova Petrol Never tried so far. I heard from my friends we can get upto 14kmpl. Maximum I achieved with Petrol Innova is 12kmpl.

Regards,

Ravi.
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Old 30th July 2007, 11:11   #7
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any ideas about indica diesel as well?
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Old 30th July 2007, 11:17   #8
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Quote:
Originally Posted by 1100D View Post
When cruising, it is best to stick to a speed corresponding to the highest gear and the rpm being the maximum torque rpm.
Is it as simple as this?? This, from how stuff works could complicate things:- for most cars, the "sweet spot" on the speedometer is in the range of 60 - 90 kmph. Cars with a higher road load will reach the sweet spot at a lower speed. Some of the main factors that determine the road load of the car are:
  • Coefficient of drag. This is an indicator of how aerodynamic a car is due only to its shape. The most aerodynamic cars today have a drag coefficient that is about half that of some pickups and SUVs.
  • Frontal area. This depends mostly on the size of the car. Big SUVs have more than double the frontal area of some small cars.
  • Weight. This affects the amount of drag the tires put on the car. Big SUVs can weigh two to three times what the smallest cars weigh.
In general, smaller, lighter, more aerodynamic cars (zen, spark, etc) will get their best mileage at higher speeds. Bigger, heavier, less aerodynamic vehicles (read SUV's) will get their best mileage at lower speeds.

In my Matiz I get best FE at 80-90 Kmph, it drops significantly above 100. This actually corresponds to what 1100D states. Do sedan and SUV owners differ?
regards.
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Old 30th July 2007, 11:22   #9
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I guess driving in top gear near the least rpm where peak torque is being produced is a good idea.
for example, if your car produces peak torque at 1700-2500rpm, around 1800-1900rpm in top gear will do.
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Old 30th July 2007, 11:26   #10
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Quote:
Originally Posted by tsk1979 View Post
I guess driving in top gear near the least rpm where peak torque is being produced is a good idea.
for example, if your car produces peak torque at 1700-2500rpm, around 1800-1900rpm in top gear will do.
Unfortunately, peak-torque for most petrol cars come at much higher rpm. A better idea would be to drive in the highest gear at low rpm that is enough to pull the car effortlessly.
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Old 30th July 2007, 21:57   #11
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I would go with what Whiteknight said. For my car the peak torque is @4750 RPM, I do not think thats the best FE band. Speed for 4750 RPM in 5th gear is likely to be around 150 KMPH.
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Old 30th July 2007, 23:10   #12
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I am a diesel head, what do I know
Long time back I used to have a petrol gypsy king(carb). It used to give best mileage at around 60kmph in 5th gear.
I guess a more aerodynamic car would have a higher speed where it would get best mileage.
So as per theory, if we drive in vacuum, driving at peak torque will get maximum mileage.
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Old 31st July 2007, 04:21   #13
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Quote:
Originally Posted by goandude View Post
Is it as simple as this?? This, from how stuff works could complicate things:- for most cars, the "sweet spot" on the speedometer is in the range of 60 - 90 kmph.
My 2 Paise.

I think that it is as simple as it sounds. Keep your engine at optimum RPM for that particular gear and do not bother about speed of the car. The speed depends on weight, Cd, wind etc but the RPM at which the engine works efficiently and hence uses minimal fuel remains the same.

My car (4 cyl) gives maximum FE when driven between 2000 - 2500 RPM. At 2000 RPM it goes at 40 mph and at 2500 RPM it goes between 65 - 68 mph. I am not sure of the gears though. I hear that Honda Civics too give max FE when driven @2500/65.
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Old 31st July 2007, 08:50   #14
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I do the following and I think I am getting the max. fuel efficiency.
1. Never hard on the pedal
2. Move to the top gear as early possible (this does not mean that you drag the car in lower speed and higher gear)
3. Use less brakes - to do that maintain speed around 60-80 kms so that you will break less, most of the time if you slow down by not accelerating will do the job.
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Old 31st July 2007, 08:54   #15
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this is a quote taken from the thread "what is the actual FE of your car" by normally crazy. "As I said - it was the FE for that particular trip at that particular point when I clicked the picture. It went down to 3.2 L / 100 Kms till I reached Panvel and then till Chembur it stayed at 8.4 L / 100 kms."
The car was a SKoda being driven at 70 kmph on cruise control. There is a picture of his speedo and tacho too. wow imagine 31 km to a litre!!
Request BHPians with trip computers in their cars to add to this thread. It would take the guesswork out of the discussion.
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