Boy, sure would like an app to do this - fuel economy app

[importune]

Also...

All engines increase in RPM as the speed is increased so this makes your car less efficient. This is also where different car profiles would come in useful. Some cars can get away with good gas mileage at 75mph but others wont.

I understand what you're trying to say, but this is incorrect. Or rather, you over-simplified. Engine speed is not proportional to vehicle speed, and vehicle speed is not proportional to gas mileage. I am not traveling 10mph at 1000rpm and 65mph at 6500rpm; likewise, I might net a higher mileage at highway speed than at town speed. Also, vehicles greatly vary in mileage depending on their coefficient of drag. For some cars, CoD is even more influential to mileage than engine size or speed, or even the cylinder count!

I believe you misread. The speed is directly proportional to your RPM, even if it is not at such a great ratio. Driving at a solid 15mph on a straight, flat surface will cause your RPMs to stick around a certain value, say 1,500RPMs. Now, if you drive the same stretch of road going at a solid 65mph, your engine will stay solid at a number much higher, say 3,000RPMs. The only reason you would get better gas mileage on the highway is the speed and the jerk (amount of acceleration or deceleration).

These formulas are solid, proven formulas. Most of the android devices have impressive hardware. And, be aware, we are not providing a solid number as your current MPG, its merely a way to measure how well you are driving, compare your current trips to past trips, and improve your overall fuel efficiency.


EDIT: Also note that these formulas will work best for comparing YOUR driving from one time to the next. The vehicle you are in does not matter, the drag of the vehicle does not matter, nothing about the vehicle matters. This is not giving you a value for your MPG, it is just telling you how close to the vehicle's optimum MPG you are getting.

(The only exception would be cars that recieve better MPG at higher or lower speeds, like 70 MPH.)

[PolyOlefin]

I believe you misread. The speed is directly proportional to your RPM, even if it is not at such a great ratio. Driving at a solid 15mph on a straight, flat surface will cause your RPMs to stick around a certain value, say 1,500RPMs. Now, if you drive the same stretch of road going at a solid 65mph, your engine will stay solid at a number much higher, say 3,000RPMs. The only reason you would get better gas mileage on the highway is the speed and the jerk (amount of acceleration or deceleration).

No sir, you are incorrect on many points. I don't mean to start a spat, but I'm compelled to correct the record for anyone who reads this thread.

Now I believe I'M the one guilty of over-simplification with my previous statement. Let me clarify and correct us both:

Your theory would be perfectly true if cars had only one forward drive gear.

I'm not sure what you mean when you say "even if it is not at such a great ratio". A car has multiple gears in an attempt to provide the optimal drive ratio at any given speed.

As an example, in my manual transmission Honda, I can drive at:

• 45mph @ 2000rpm in 6th gear
• 45mph @ 3100rpm in 5th gear
• 45mph @ 4500rpm in 4th gear
• 45mph @ 5800rpm in 3th gear

Vehicle speed is most certainly NOT directly proportional to your engine speed (RPM). I believe you are accustomed to an automatic transmission that does a good job choosing the optimal ratio at any given moment, but it still utilizes multiple gears to do this.

If you'll allow me to quote a snippet of myself from another forum...

Fuel economy is not directly proportional to RPMs. The determining factor is engine load.

Engine speed is easier to grasp than total load so most people try to relate RPMs with mileage. This isn't accurate.

Don't hesitate to downshift for inclines; for example, traveling up a moderate hill at 2000rpms in 6th gear will put a greater load on your engine than if it could tap a comfortable 70hp @ 3000rpms in 5th gear and reduce the overall load. This will yield better mileage, despite operating at a higher engine speed.
Don't go neutral when going downhill. Just stay in a comfortable high gear and let your fuel injectors stop (not to mention, recharge your battery).

Driving in the city, my vehicle would get the best mileage traveling about 30mph in 4th gear @ 2000rpms. On the highway, It would get the best mileage traveling about 55mph in 6th gear @ 2500rpms (practicality aside). Engine speed is only one factor in how fast a vehicle travels.

You also stated that during steady highway driving, acceleration is the only involved variable in mileage, which isn't entirely correct. Air resistance increases at roughly the cube of the speed, reducing mileage exponentially above a certain point (for most passenger cars, the "sweet spot" hovers around 55-60mph).

I shortened the relevant Wikipedia quote:
"Driving at 45 rather than 65 mph results in about one-third the power to overcome wind resistance, or about one-half the energy per unit distance, and much greater fuel economy can be achieved. Increasing speed to 90 mph increases the power requirement by 2.6 times, the energy by 1.9 times, and decreases fuel economy."

Again, I'm not trying to light a fire under your balls or anything, I just can't allow people to be misinformed. Like I've told other people, I'm not like this because I'm an engineer, I'm an engineer because I'm like this.

[iPirate]

The point of this app is to give you an idea of how you are driving. Obviously there are a million different things that could happen but there is also a "best guess" and that is what will be offered. Nobody is being misinformed, nobody suggested this app is going to give you results accurate enough you can take to court.

Have you tried using the app? I would love some more feedback.

[PolyOlefin]

I understand the app isn't meant to be a tool for scientists or anything. Didn't mean to be on the attack, I just had an issue with the "speed is directly proportional to RPMs" bit.

I'll be picking up a bluetooth OBDII adapter soon, do I still have to PM you for the download? Also if your app uses GPS I'll have to do a wipe first since my ROM is making some hardware functions bug out... But I'd definitely be happy to give some feedback once I get things running.

[iPirate]

I understand the app isn't meant to be a tool for scientists or anything. Didn't mean to be on the attack, I just had an issue with the "speed is directly proportional to RPMs" bit.

I'll be picking up a bluetooth OBDII adapter soon, do I still have to PM you for the download? Also if your app uses GPS I'll have to do a wipe first since my ROM is making some hardware functions bug out... But I'd definitely be happy to give some feedback once I get things running.

No PM required.

http://dl.dropbox.com/u/5961718/BeGr...enbeta.2.4.apk

The app does use GPS though!

[iPirate]

I haven't updated in a while.

I am working on the app but got a little busy at work and haven't been able to put as many hours as I would have liked to.

I'm less busy now and should have something nice on the market soon!

I would like to hear feedback about the current state of the app as well!

[cyber3dx]

I'll tell ya, for me, I gotta have some sort of graph or chart or somethin' to show me how my driving style affects my economy real time.

You've done such a great job on this app.

Awesome.