Speed kills...

[jim-frank]

I had to make a quick comment. In some cars, (specifically my Nissan Sentra), the fuel injection and gearing is set up so that mileage actually peaks at certain speeds.My Sentra increases mpg up to about 69 mph. This is probably due to the efficiency of a piston engine decreasing with decreasing load. In any case, I get 42 mpg at 55 mph, and 49-51 mpg at 69 mph.

Speed doesn't always penalize your tank. This is a really good reason to obtain some kind of mpg monitor and learn what your vehicle is really doing as opposed to what it's theoretically doing...

[groar]

Originally Posted by jim-frank

In any case, I get 42 mpg at 55 mph, and 49-51 mpg at 69 mph.

What are your rpm and gear at 55 and 69 mph ?
At which rpm is your best torque ?

Speed doesn't always penalize your tank. This is a really good reason to obtain some kind of mpg monitor and learn what your vehicle is really doing as opposed to what it's theoretically doing...

On Toulouse beltway, the speed was lowered from 110 km/h to 90 for cars and 80 for trucks. The CO2 emissions, and so the consumptions, have been lowered a lot (ie more than the 18% corresponding to the speed change), but for some trucks it's greater because they have to be in a lower gear.

To several people, with instant feed back in their cars, I talked about my eco-driving style.
When I talk about obeying to speed limits and having moderate acceleration (yes about that tip every car is unique and some may prefer harder accelerations) they are ready to try and they try indeed.
When I talk about understanding how the car works just by reading the instant feed-back, very few listen and people who try don't do it a long time.

If I have only one tip to communicate it will be "go slower", even if for some cars the FE will be lower, because as a whole the FE will be greater. To people willing to improve more, I'll give them my theoretical knowledge of cars and explain them how to try to improve more.

From what I heard here and there, the best economy is *generally* around the best torque rpm. Empirically on my wife's diesel (best torque at 1500rpm and barely usable under) with instant feed-back the lower rpm the best FE, but all cars are unique (as wives ). I don't have instant feed-back on my older diesel, so I have to use what I hear and what I can see on a very different diesel to improve myself on my car.

Since my beginning I tried to lower my speed and moderate my accelerations, as I had a lead foot. The first tank was primarily based on that and I lowered my consumption by 15%. If only all people I know could do so then it would be a better world...
During my second tank I continued to monitor my speed, but also tried to use DFCO and better know my route to start DFCO sooner and stop acceleration sooner. The result climbed to 30%.
Now my knowledge of my car is theoritical, but I know the best torque rpm, the rpm/speed of each gear... and what my ECU controls. From that it seams that I may not have DFCO as my wife's car, so since this tank I'm using NICE-On Coasting. At the end of the current tank, I'll try to use the result to improve myself during next tanks.

Now I would like to have a compatible monitoring system, but the SG2 isn't and as my hands aren't able to do more than a bulb change I'll have to improve myself slowly, "one tank at a time", by using knowledge published here by other people.

Thanks to all these people publishing their theoretical and/or empirical knowledge.

Denis.

[jim-frank]

Originally Posted by groar

What are your rpm and gear at 55 and 69 mph ?
At which rpm is your best torque ?

That's in fifth gear, but I don't have a tach so I don't know the rpm right off hand. The GA16DE engine in my Sentra has a broad torque peak from about 3200-3800 according to listed specs.

I agree that, in general, reducing speed will improve mileage. That's inevitable since the air resistance scales with the square of the airspeed. If a person is driving numbly, with no other care than maintaining a constant speed, they will probably get small but consistent gains from travelling at a lower speed.

The problem is this: the idea that reducing speed will always reduce fuel comsumption is based on an oversimplification. What's oversimplified is the assumption that the engine is equally efficient at all rpm and load conditions. The success of P&G techniques highlights the gross inefficiency of lightly loaded piston engines.

I was really amazed at the 74 mpg I was getting with the P&G technique. I'm trying it around town as I commute to work and such. It will be interesting to see how it works at lower speeds.

[superchow]

Originally Posted by IndyIan

...Get a rifle case for an ATV and mount it on your scooter across the back, maybe add a NRA sticker too for those who don't know what the case is for.

It might get them thinking you're a bit nuts and give you some space

EPIC!

[Katana]

Someone always joked to me when they heard that "speed doesn't kill, it's the sudden stop."

[groar]

Originally Posted by Katana

Someone always joked to me when they heard that "speed doesn't kill, it's the sudden stop."

I do love that humor

But someone here will say that it isn't true at 100%, per example your car can be hit by a train and be pushed during miles...

Denis.