26.5 mpg wtf

[RichardsFRS]

Someone asked how I'm measuring. I'm going off the readout on dash. I'm guessing it's a combined. I haven't taken any mathmetical measurements. I tried the 65 mph thing going home. Ugh

[Dadhawk]

Originally Posted by Packofcrows

what has elevation been? weight? fuel type (91 only in CA doesnt give as much mpg as 93, the recommended one) how often stops? Weather/temp? etc..

Most of the miles put on my car are at an elevation of 1,000ft or higher (Atlanta metro varies from 700 to 1300 feet but the "official" altitude is a little over 1,000ft). Most of the trips quoted included at least some partial travel up to 5,500ft but some also included closer to sea level.


Fuel is always 93 on these trips. Car is stock so the variation in weight would be passenger and luggage. A couple of the trips were two passengers, and fully loaded with luggage (say 350 to 400lbs), but most were single passenger, minimal luggage (under 250lbs total).


Trips were measured nearly full highway miles, no stops between fuel ups except variations in traffic, and usually fueled up right off the ramps. Lifetime is typical commuting which involves all the variations of daily driving.

[R2RO]

My average when my car was N/A was around 30 mpg.
Now that its turbocharged I get around close to 21 mpg or less since I love that BOV sound

[Nickosport]

According to the trip computer I get 28.7mpg, exclusively city miles - no highway. You guys must beat the hell out of these cars daily to get the MPG I see on here. I don't go nuts, but I don't baby it either. 26 miles each way through Atlanta traffic, and my MPG is not bad, its actually about the same as the 2012 Sentra I used to have

[Stang70Fastback]

Guys, keep in mind, I'm pretty sure the trip computer isn't just overestimating by 1.5 MPG on my car. Id be willing to bet similar discrepancies for most of yours as well.

[Tcoat]

Originally Posted by Stang70Fastback

Guys, keep in mind, I'm pretty sure the trip computer isn't just overestimating by 1.5 MPG on my car. Id be willing to bet similar discrepancies for most of yours as well.

I calculated my milage for a few months and found that the trip calculator was usually off by about the same as yours. Since it was so consistent I now just use it and remove the 1.5 from the figure.

[Dadhawk]

Originally Posted by Stang70Fastback

Guys, keep in mind, I'm pretty sure the trip computer isn't just overestimating by 1.5 MPG on my car. Id be willing to bet similar discrepancies for most of yours as well.

That's pretty close to my observation. Calculated over 77,000 miles my average is 32.7. The trip computer, which to my knowledge has never been reset, although it is possible the battery may have been disconnected at some service somewhere, shows 33.7.


Both methods are subject to some level of error. Using the fill and calculate will tend to run a little low over time because of the differences in what 'full' means based on how the car is sitting when filled and other variables (you are more likely to underfill it to "full" than overfill it). Depending on whether or not the computer uses real fuel flow versus some other estimate it can have its own share of errors.

[Stang70Fastback]

Originally Posted by Dadhawk

Both methods are subject to some level of error. Using the fill and calculate will tend to run a little low over time because of the differences in what 'full' means based on how the car is sitting when filled and other variables (you are more likely to underfill it to "full" than overfill it). Depending on whether or not the computer uses real fuel flow versus some other estimate it can have its own share of errors.

Actually, they aren't subject to the same error. The car calculates fuel consumption based on, essentially, a whole bunch of sensor readings, and determines what it *thinks* you are getting. This is an "ideal world" scenario where engineers have determined a formula for the vehicle to use. The car can't account for all parameters, so the formula is an estimate. It never actually KNOWS exactly how much fuel it is using, nor does it actually ever know how much gas you put in the tank. It can only estimate those values.

Calculating fuel usage yourself, however, is extremely accurate, as you are eliminating a lot of potential for error, and are left with a few basic assumptions:

1. Is your odometer accurate? For all intents and purposes, yes. Assuming you aren't using the trip meter, it's only accurate to the nearest mile, but even across one 30 MPG tank, that will only throw off your estimate by a small amount.

2. Is the pump dispenser accurate? For all intents and purposes, yes. LEGALLY, they are required to be INCREDIBLY accurate.

As far as whether or not your tank always fills to the same level, you are correct, there are differences based on how your car is sitting, and how sensitive the pump shutoff is, however these errors only matter on the very LAST fill-up that you are including in your measurements. If you are calculating an average across a bunch of fuel-ups, then the errors introduced in-between don't mean anything. You know how MUCH fuel was put into your car across all the stops, you just can't be sure that your last fuel-up accurately states exactly how much fuel you used since the previous one, because it might not have filled to exactly the same spot.

Essentially, all of these potential errors, if you distribute them over several fuel ups, become statistically insignificant. If you do the math over my 25,000 miles, or your 77,000 miles, you can be pretty damned sure that the number you come up with is pretty much EXACTLY what your actual average fuel economy is.

This is, of course, assuming you can properly read the pump, and record the numbers, and do the math without screwing up, lol

[RichardsFRS]

Originally Posted by Nickosport

According to the trip computer I get 28.7mpg, exclusively city miles - no highway. You guys must beat the hell out of these cars daily to get the MPG I see on here. I don't go nuts, but I don't baby it either. 26 miles each way through Atlanta traffic, and my MPG is not bad, its actually about the same as the 2012 Sentra I used to have

26 miles one way thru atl for me. From flowery Branch to norcross. Yea I drive pretty hard.

[fumanchu1]

Originally Posted by shiumai

17 to 18 mpg city. Now 15.5 soopahcharged

You're not pressing hard enough on the right pedal


What are you running if I may ask? (I run a Kw C38 kit if you wanted to know)

[shiumai]

Originally Posted by fumanchu1

You're not pressing hard enough on the right pedal

What are you running if I may ask? (I run a Kw C38 kit if you wanted to know)

I'm running the edelbrock e-force kit. Since i have such a short commute (4 miles each way), i don't really care about mpg since I only fill up every three weeks. my BRZ is almost 3 years old and i'm just at 7500 miles.
i'm just happy i'm getting better gas mileage than my previous car; a '78 Datsun 280Z with triple webers. i got 12-13 mpg out of that for the same route.

[Stang70Fastback]

Originally Posted by shiumai

I'm running the edelbrock e-force kit. Since i have such a short commute (4 miles each way), i don't really care about mpg since I only fill up every three weeks. my BRZ is almost 3 years old and i'm just at 7500 miles.
i'm just happy i'm getting better gas mileage than my previous car; a '78 Datsun 280Z with triple webers. i got 12-13 mpg out of that for the same route.

I'm confused. Do you use the BRZ for track days, or weekend getaways? You make it sound like literally the only thing you use it for is an 8 mile commute to-and-from work, in which case I can't possibly fathom why you bought it, lol.

[soulreapersteve]

Originally Posted by Stang70Fastback

Guys, keep in mind, I'm pretty sure the trip computer isn't just overestimating by 1.5 MPG on my car. Id be willing to bet similar discrepancies for most of yours as well.

Originally Posted by Tcoat

I calculated my milage for a few months and found that the trip calculator was usually off by about the same as yours. Since it was so consistent I now just use it and remove the 1.5 from the figure.

Holy crap. Since this is the case, I'm getting 19.5mpg.

Yay evening traffic! Luckily, mornings are relatively easy. Think I may switch back to full auto to get back up to 28.

[Tcoat]

Originally Posted by soulreapersteve

Holy crap. Since this is the case, I'm getting 19.5mpg.

Yay evening traffic! Luckily, mornings are relatively easy. Think I may switch back to full auto to get back up to 28.

Gotta pay to play!