Which method would yield better fuel mileage?

Car: G35 6MT

Scenario A: You're driving a short distance from A to B. It's 30% city then 70% freeway. Assume there's no traffic, just a nice sunday cruise with light traffic.

Assumption: Best fuel mileage is obtained when you drive at the highest gear when possible.

Method 1:
You drive like a granny. Meaning, you're changing gears under 2500k rpm. Takes you longer to reach your highest gear (6th), but you're light on the gas pedal. Once on the freeway, you coast at 3k rpm.

Method 2:
You drive more aggressively. Meaning, you're changing gears at ~5k rpm (never redlining). You reach 6th gear faster and you also cruise on the highway around 3k rpm.

This is the debate i've had with a buddy. I believe method 1 will be more fuel efficient because most of the fuel consumed at low gears and with a heavy foot. What are your thoughts?

 

Internal combustion engines are most efficent at WOT.

So in theory accelerating at full throttle up to speed and then crusing at what ever speed should get you the best gas milage.

 

If the freeway (c'mon...... you call it a highway) is the 401 then you know your milage will suck regardless!!!!! LOL

 

Without a doubt, method 1 will be more fuel effecient.

 

anyone else have any add ons? I believe method 1 to be true too but Im wondering if its other wise...

 

Just start it in 6th gear next time.

 

+1 Short shift it and cruise.

What will astound you is how much better mileage you will get by just going 65 mph rather than 70 mph. I tried it in my company car (2004 Grand Prix) and it went from 24 mpg to 28 mpg.

 

 

Method 1 no question. Light throttle,short shifts and lower speeds will win every time.

 

I disagree. The only reason method 1 will yield better mileage (and not much mind you) is because you have gone slower for longer.

It takes the same amount of work to get the car up to any speed, regardless of gearing/rpm. All the gearing does is limit how fast the speed can increase by the limits of the engine's torque.

So.... it's not because of lower rpms/granny shifting, but rather because you are accelerating more slowly and therefore have a lower average speed. You would get the same mileage if you shifted at 6k but did not use any more throttle than in granny-mode... you'd be in each gear longer and probably skip a gear or two at your chosen top speed, but it would be the same fuel consumption.

Can someone tell me where my logic is broken?

I've played around with this a lot with my realtime MPG display and it sorta proves this to be the case. What causes high consumption is high work... fast acceleration or even just maintaining speed up a steep hill... usually directly tied to throttle but limited by how much the engine can use your throttle position given the torque/rpm/gearing.

 

I was always taught that if you drive like you had an egg between your food and the gas pedal, you would get great mileage. I have found this to be true.

 

+1

 

mal is right... by accelerating slowly you are spending more time in the "low MPG range". And whats worse.. you are in the engine's most INEFFICIENT range (out of torque peak).

But in reality.. this number is so small that it doesn't really matter over a 100 mile trip.

So, if you cruise at 3000 rpms you'll get pretty good mpg.. I usually get 28 or so on my long drives using my method which i'm sure is right around what the granny method gets.

 

You also have to VALUE your time.
For my commute, i can do about 95% of it with cruise control on at 60.
Or I can go 90.
Once you're in last gear, the ratio of rpm/mph is getting infinatly higher as you speed up. Also at 60mph, roughly 90% of your fuel consmption is to overcome drag and resistance. The lower you keep it in last gear, the more efficient.
But if that saves you one gallon per trip, but you'de make 10$ by being at your destinatin 20 minutes earlier, then its more echinomical to hurry up and get there......

 

yeah... i'm going to write one more to see if I can be clearer...

it takes the same amount of work to accomplish the same task, regardless of how you do it.

So, if you get from point a to point b in the same amount of TIME, you'll use the same fuel. This is not true if you throw in a lot of braking -- braking converts velocity (kinetic energy) into HEAT and hands it over to the air. But... given comparable braking, the granny or aggressive methods, IF they arrive at point B in the same number of minutes, use the same fuel.

hmmmm.. maybe that's not any clearer