[Skibum]

I think I have determined that the 409 designation for max MPG is more than a bizarre design artifact, it's affirmatively messing up MPG calculations.

I have been tracking gas I purchase. Easy to do since so much of my driving is local and thus I haven't been buying much. Have only taken one long trip where I needed the ICE.

Thus far I have 1090 miles on the car, and have only purchased 11 gallons of gas. Tank is currently full, so I should be reporting 100 MPG (99 if you want to be a stickler about it...).

However, the Karma is reporting me at 85. I'm pretty sure it's because it won't acknowledge anything over 409 MPG.

Here's my math - feel free to tell me if I'm missing something: if you assume I am getting 25 MPG while the ICE is running, then 11 gallons gets me 275 miles, leaving 805 miles. If 409 is the max the car will recognize, then it thinks I have burned another 2 gallons going that distance. Adding that to the 11 I have actually used, the car thinks I have used 13 gallons. Over 1090 miles, that would yield an MPG of 84 - almost exactly what the Karma is reporting.

So...moral of the story: don't believe the MPG calculations at the higher ranges.

Nimisys: any word on whether this is something they will address in 6.15?

 

[Fabulist]

I think I have determined that the 409 designation for max MPG is more than a bizarre design artifact, it's affirmatively messing up MPG calculations.

I have been tracking gas I purchase. Easy to do since so much of my driving is local and thus I haven't been buying much. Have only taken one long trip where I needed the ICE.

Thus far I have 1090 miles on the car, and have only purchased 11 gallons of gas. Tank is currently full, so I should be reporting 100 MPG (99 if you want to be a stickler about it...).

However, the Karma is reporting me at 85. I'm pretty sure it's because it won't acknowledge anything over 409 MPG.

Here's my math - feel free to tell me if I'm missing something: if you assume I am getting 25 MPG while the ICE is running, then 11 gallons gets me 275 miles, leaving 805 miles. If 409 is the max the car will recognize, then it thinks I have burned another 2 gallons going that distance. Adding that to the 11 I have actually used, the car thinks I have used 13 gallons. Over 1090 miles, that would yield an MPG of 84 - almost exactly what the Karma is reporting.

So...moral of the story: don't believe the MPG calculations at the higher ranges.

Nimisys: any word on whether this is something they will address in 6.15?

Part of the problem may be that you have not accounted for the gas burned after you fill the tank for purging the lines or whatever. I am not sure that would account for the full 1.8 extra gallons consumed, but that could be some of it.

 

[SoCalGuy]

I'm not sure the MPG calcs are accurate. I've been operating mostly in Sport mode and note the odo/tripometer mileage after a fill up and the amount of gas (for previous trip). My calcs show me at around 21MPG or so consistently, while the Karma MPG calc shows 24 or 25 MPG for the same trip. That's a difference of 26 - 34 miles range, so definitely noticeable (8.5 gallons usually for a fill up x 3 MPG and 4MPG). Has anyone else experienced this?

 

[Nimisys]

Nimisys: any word on whether this is something they will address in 6.15?

Given the other issues i run into on a daily basis, honestly, this is one thing i have never inquired about. Until i started coming here, i didn't even know 409 was the max amount it would display. I can ask about it, but i don't think it is a priority fix for right now

 

[Dutch]

The difference between 85 and 99 mpg is too small to draw any conclusions, especially when you've only driven 1090 miles. This difference can be explained by the difference between filling up the tank at two different gas stations (some pistols fill up a tank more than others) or by two different people (the dealer and you; some people try to put in more than others).

 

[Fabulist]

Real MPG vs. Estimate

I finally made it to Costco today to fill up the gas tank. I almost always fill up there on my way to work in the mornings so the ambient conditions and pump pressure do not vary very much with each fill up.

Here is a shot of my energy screen right before I filled up the tank:

To fill up the car, I put in 9.2 Gallons, which actually concerned me a bit about how close I came to flaming out, but the actual gas mileage for this cycle was 750/9.2 = 81.52 MPG, which is impressive to be sure, but significantly less than the 102 MPG estimated by the computer.

When a car's trip computer estimates the MPG, they tend to be off because even though they can measure the miles pretty accurately, most cars don't have sensors that measure actual fuel flow but have to estimate it from fuel pressure, which leads to inaccuracy. Not sure if this can be improved by changing the algorithm, or if it would require new or different sensors.

 

[SoCalGuy]

RE: Real MPG vs. Estimate

I finally made it to Costco today to fill up the gas tank. I almost always fill up there on my way to work in the mornings so the ambient conditions and pump pressure do not vary very much with each fill up.

Here is a shot of my energy screen right before I filled up the tank:

To fill up the car, I put in 9.2 Gallons, which actually concerned me a bit about how close I came to flaming out, but the actual gas mileage for this cycle was 750/9.2 = 81.52 MPG, which is impressive to be sure, but significantly less than the 102 MPG estimated by the computer.

When a car's trip computer estimates the MPG, they tend to be off because even though they can measure the miles pretty accurately, most cars don't have sensors that measure actual fuel flow but have to estimate it from fuel pressure, which leads to inaccuracy. Not sure if this can be improved by changing the algorithm, or if it would require new or different sensors.

Perhaps that explains why my calcs show my range extend Sport mode MPG at 21MPG while the Karma computer shows 24MPG.

 

[dennis]

RE: Real MPG vs. Estimate

Perhaps that explains why my calcs show my range extend Sport mode MPG at 21MPG while the Karma computer shows 24MPG.

It could also be Henrik math:

32 = 50
21 = 24
85 = 102

 

[ct-fiskerbuzz]

RE: Real MPG vs. Estimate

It could also be Henrik math:

32 = 50
21 = 24
85 = 102

You forgot the last one: 409 = infinity.

 

[SoCalGuy]

RE: Real MPG vs. Estimate

It could also be Henrik math:

32 = 50
21 = 24
85 = 102

You forgot the last one: 409 = infinity.

And this one: 2009 = 2012