pradeepa

I once read on the XBhp magazine that higher revs gulp more fuel.

Recently while trying to understand engine perfomance characteristics, i read on quite a few websites, that an engine delivers the maximum fuel efficiency when its running at an RPM which delivers the maximum torque.

I guess most of the indian motorcycles deliver the maximum torque at 6000 RPM, so does that mean that if an engine is running at 6000 RPM then it will consume more fuel than riding at 4000 RPM.

Is it the throttle position which determines the fuel consumption or the RPM at which the engine is running?

Noor

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princesirohi

• engine RPM is directly proportional to throttle position. ofcourse it also depends on lot of other factors- like load etc.
• yes maximum fuel efficiency is obtained at a point somewhere near maximum torque point.
• but fuel consumptioin also depends on other factors also - for xample - which gear you are riding in.

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HarishK

I think you want to know which is the best spot to hold the throttle to have the Fuel Consumption is Balanced.

Is it correct???

Lets take the R15 for instance,

Also let the drive terrain be a Highway

The bike peaks out the torque at 7-7.5K , doesn't mean that bike will not have anymore torque left.

So keeping the bike at its best torque is definitely going to consume more fuel than keeping the throttle at 4000RPM in the same gear.

But the main Factor is that bike balances itself in the Maximum torque region, You cover more kms when compared to the more fuel consumed. While at 4000RPM, offcourse the bike consumes less fuel than 7K RPM, but propels you to even less distance, resulting in a greater fuel consumption.

So its always better to maintian an R15 between 6000 to 7000RPM on a Highway to run more kms per liter fuel.

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Samarth 619

Commuter bikes have a max torque as low as 3500-5000 rpm. But still you take 6000 rpm having max torque for example, ok?

At 6000 rpm, your speed is around 75 kmph. At 4000 rpm, your speed is 50 kmph. So, the distance you travel is more at 6000 rpm.

Now relating distance travelled to fuel consumption, if a bike makes good torque at a particular rpm, it runs stress free and healthy at that rpm. And it is less affected by tailwinds, headwinds, up-slopes, etc. Hence, constant throttle is maintainable which makes it fuel efficient.

Both.
If your rpm is low, and throttle is high, (pulling in higher gear) you won't get good mileage,
If your rpm is very high, around max power spot, and throttle is high too, you won't get very good mileage, (because throttle at max torque point is often around 40% compared to 80-90% for power spot. Estimated figures)

For ideal mileage, rpm should be somewhere in the middle of powerband, and throttle should be the "least possible" required to maintain the above rpm. Simple.

pradeepa

Actually i think i should have rephrased my question: if i want to travel at 40kmph, i can do that in two ways considering the gear ratios:
1) travel in 2nd gear at 5000rpm
2) travel in 3rd gear at 3500rpm
The power-band of this motorcycle lies in the range of 4000-6000rpm.
Which gear/rpm should i choose for maximum fuel efficiency?


i think i have found the answer: it depends purely on the throttle position. That is fuel consumption is directly propotional to throttle position.

If i have to give more throttle input for using option 1, then i will be consuming more fuel while riding in second gear.

I think that we should choose the right gear which can maintain our desired speed and also deliver sufficient torque to overcome the frictional resistance and wind resistance and gravitational force with minimum throttle input.

So for acceleration, i think, we should keep the engine in its power-band.
But for maintaining a constant speed, i think, its not necessary to use the power-band of the engine.

PS: i was recently riding a bicycle after a long time and noticed how much strength i had to use to accelerate the bicycle. But if i had to maintain a constant speed, it was far easier. So the botttom-line was it takes less fuel to maintain a constant speed, but a lot more, to accelerate.

jd666

Basically once the engine reaches 6000 rpm, you can ease off the throttle, and reduce the fuel flow to the engine and bring it into cruise mode. i.e. amount of fuel needed to maintain 6000 rpm. ( generally it can be felt, that at peak torque rpm level, you can ease off the throttle a lil bit ).

So if you are cruising steady at 6000 rpm, your engine is in the most efficient zone of torque output.

But it also depends on what gear are you in.

For eg in 5th you would be cruising at say 80 kmph.

In 4th you would be doing 60 kmph.

In one hour for the same fuel consumption ( considering all factors are ideal ), you get 60 kms of mileage in 4th and 80 kms in 5th.

So gearing plays a very important role.

There have been numerous tests, the most recent that i remember in TG or somewhere, that the sooner you get to top gear ( accelerating properly, not just upshifting as soon as you can ), the more efficient your driving/riding is.

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Samarth 619

Its more like speed to throttle which decides the mileage. Going on constant higher speeds on lower throttle is the key. If you notice, you spend the first 20-30% throttle in reaching almost 50% speeds, then as the throttle increases by bigger margin, speed increases marginally.
For example, try reaching 60 kmph on your bike. You'll reach in 30-35% throttle or so... But 120 is not reached in 60% throttle, its reached around 80-90% I think.
(Above are Estimated figures made to prove a genuine point.)

As for your question, its better to go @ 3500 rpm in 3rd, if the torque is roughly equal or similar to 5000 rpm's torque. A dyno Graph is still needed for such conclusions though...

But for any one particular gear, more mileage is obtained near the torque spot at minimum possible throttle. And you can maintain more consistency under headwinds, tailwinds, upslopes, etc.

Honda_CBF

For max fuel efficiency how about riding below 3k rpm (without lugging the engine) on a bike which produces max torque around 6-6.5k rpm??
Asking because I do that as my daily commute road is like sh**

Samarth 619

Yes, it gives good mileage anyways. But its still not the optimum place to be, if any one gear is in question (say for example, the 5th gear).

The "40-50 kmpl is the ideal zone" thinking comes from 100cc bikes which make max torque around this spot. But the same is not true for our performance bikes, which might deliver enough torque to "carry" it at 40 in top gear but the mileage can be optimum still by riding at torque spot...

On my trip to Jaipur once, I received fairly good mileage while riding around 7-8000 rpm all the way. This shows that on 6000 rpm it might just better the reading...