Mileage vs Speed
I was driving through the beautiful stretch of the newly laid 4 lane road of NH2 which is part of the Golden Quadrilateral (GQ) from Hazaribagh towards Varanasi. Incidentally that stretch of GQ is a concrete surface and not a bitumen one. The roads were empty with no sign of vehicles for kilometres all together. The roads were so straight, where you can even see the horizon merging into the end of the road as if the road itself is a pathway to heaven.
Sighting that never ending road in front of me, I was holding the steering wheel with that amazing machine at the touch of my foot pedal, which if I press will kiss 180 kmph without a second thought. Still the dilemma was hazing my thoughts, whether to push it as my heart wanted it to or listen to my mind and save a lot of money.
Mileage vs Speed was the debate between my heart and my mind.
Aiming for Mileage:
After all these years of driving, I have realised that to get the maximum fuel efficiency from a car one should drive just below 100 kmph and just below 3K RPM of the engine. There’s no hard and fast rule to this theory however with all the permutation combinations that I have tried all these years, I have reached towards this conclusion.
It is also evident that beyond 100 kmph, every increase of 10 kmph results in the mileage to drop by 2 kmpl. Hence, if you were getting a mileage of 16 kmpl at 100 kmph, if you increase the speed to 110 kmph then mileage will fall down to 14 kmph, at 120 it will be 12, at 130 it will be 10 and beyond 140 or 150 it will be simply pathetic.
When I was driving from Bangalore to Hyderabad on my 3rd instance, I decided to aim for the best possible mileage and my 7+ year old car which is a petrol sedan, with 5 passengers and full AC on returned a mileage of 17 kmpl. That’s a lot. In the city it never gives more than 10.
Relation between Speed and RPM:
If the vehicle is moving in the 5th gear just under 100 kmph, you will notice that the RPM is just below 3. However if the gears are lower, RPM at the same speed will be much higher. The relation between these two variables is quite simple; we can achieve the maximum fuel efficiency from the car if we just stick under 3K RPM whatever be the gear. Since 5th gear will give maximum speed under 3 RPM, the vehicle will move the maximum distance and hence more efficiency.
Gunning for Speed:
After all, when we are on the highway not always we can stick under 100 kmph. We have distances to cover, destinations to meet and many a times with time constraints. In these situations it doesn’t really make sense to stick under 100 kmph when the roads are so inviting that one can comfortably cross 150. When I was going to Gir, Gujarat from Mumbai I had to cover a distance of 980 km during the day time. I left morning 6 AM but I knew that if I aim for mileage I will not reach my destination in time. Since I wanted to reach before dark so I had to push and I did push to 175 kmph on many occasions. Obviously the roads were also good enough for me to do that.
If there is no hurry to reach to the destination, if you have enough time available to complete the journey, if there are no set time targets then one should Aim for Mileage. However when the distances are long and there is time constraint involved then it’s advisable to Gun for Speed. In my driving experience, when I have around 500 km to cover in a day I go for mileage, since I know that I can easily cover that 500 km in about 8 hours. However whenever I drive for 1000 km in a day then I always drive as fast as a can to reach to my destination and complete the journey during the day time. Usually it takes around 14-15 hours for 1000 km, hence can’t stick below 100 kmph.
Now would you like to know what decision I took when I was facing that dilemma on the NH2 GQ between Hazaribagh and Varanasi? Yes! I agreed to listen to my heart and I pushed the gas to drive above 170 kmph and kept my mind aside for my next journey.