(ummm... a mouthful of a title, isn't it? 
)
OK, this is bugging me... I'm always wondering about the accuracy of the "Average mpg" displayed on the Trip info. Thinking that it's set to overoptimistic for PR reasons, but not sure about how much, if in fact at all. Much earlier rough calcs suggested ours may be about 0.5mpg overestimating but I can't imagine that's always the case.
Did it again on a recent trip and there I had one case of overestimating by 6% and one (more questionable) underestimating so who knows.
So here is your chance to post your numbers for folks to compare to their numbers. And maybe we could even make some sense of this.
One might assume that the number is based only on the odometer and the fuel gauge sensor signal. (is that for sure?)
But I'd suggest a few ground rules to try and maximize the usefulness of the numbers:
- let's limit this to a full tank used or very close to minimize errors.
- Got to be done by topping off the tank (preferably with the exact same pump if you want folks to be in awe of your experimental method ).
- if you saw the number changing just before you filled up, use the "intermediate" value. (E.g. if it just went from 17.9 to 17.6mpg, use 17.7 or 17.8.) (What's with the poor resolution of that thing...?)
- You must include the tire size correction in your calc and state what that is. If you have a device that does that automatically, please state so.
- Note whether you have used the " tire size calibration" feature on the Nav Sys or not. This is a murky issue but the general feel seems to have been that this calibration has no bearing on the "avg mpg" calc, just for dead reckoning for navigation. Not sure. (Additional or more specific info welcome.) But we'll include it just in case it may affect the average mpg calc, never knows.
- use US miles and gallons, with apologies to our Commonwealth friends
- round off to third digit
- feel free to add comments as you see fit. Owners of aftermarket gauges (SG, UG) feel free to include those numbers in comments as well if you think it is interesting.
Let's use the following format (with some real recent numbers of mine as example although flawed cuz not the same pump and not a full tank):
------------
Displayed average: 17.8 mpg
Calculated average after tire size correction: 17.8 mpg
Tire size correction used in my calcs: 6% (33" tires)
Distance covered after tire size correction: 239.6 mi
Gallons used: 13.52 gals
Did do the "tire size calibration" in the Settings screen with the current tires: ooops, don't recall.
Same exact pump: No.
Comments: almost entirely freeway, 35psi in Revo 33"s, 87 oct, A/C on, 65 mph mostly, 4 people plus full luggage, all stock except for tires. Strangely or coincidentally, the displayed value was right on, which may mean that it was 6% overoptimistic -or more unlikely that this tire size calibration works, assuming I even used it.
------------
Care to help us figure this out so we know how accurate these things are?
)OK, this is bugging me... I'm always wondering about the accuracy of the "Average mpg" displayed on the Trip info. Thinking that it's set to overoptimistic for PR reasons, but not sure about how much, if in fact at all. Much earlier rough calcs suggested ours may be about 0.5mpg overestimating but I can't imagine that's always the case.
Did it again on a recent trip and there I had one case of overestimating by 6% and one (more questionable) underestimating so who knows.
So here is your chance to post your numbers for folks to compare to their numbers. And maybe we could even make some sense of this.
One might assume that the number is based only on the odometer and the fuel gauge sensor signal. (is that for sure?)
But I'd suggest a few ground rules to try and maximize the usefulness of the numbers:
- let's limit this to a full tank used or very close to minimize errors.
- Got to be done by topping off the tank (preferably with the exact same pump if you want folks to be in awe of your experimental method
).- if you saw the number changing just before you filled up, use the "intermediate" value. (E.g. if it just went from 17.9 to 17.6mpg, use 17.7 or 17.8.) (What's with the poor resolution of that thing...?)
- You must include the tire size correction in your calc and state what that is. If you have a device that does that automatically, please state so.
- Note whether you have used the " tire size calibration" feature on the Nav Sys or not. This is a murky issue but the general feel seems to have been that this calibration has no bearing on the "avg mpg" calc, just for dead reckoning for navigation. Not sure. (Additional or more specific info welcome.) But we'll include it just in case it may affect the average mpg calc, never knows.
- use US miles and gallons, with apologies to our Commonwealth friends
- round off to third digit
- feel free to add comments as you see fit. Owners of aftermarket gauges (SG, UG) feel free to include those numbers in comments as well if you think it is interesting.
Let's use the following format (with some real recent numbers of mine as example although flawed cuz not the same pump and not a full tank):
------------
Displayed average: 17.8 mpg
Calculated average after tire size correction: 17.8 mpg
Tire size correction used in my calcs: 6% (33" tires)
Distance covered after tire size correction: 239.6 mi
Gallons used: 13.52 gals
Did do the "tire size calibration" in the Settings screen with the current tires: ooops, don't recall.
Same exact pump: No.
Comments: almost entirely freeway, 35psi in Revo 33"s, 87 oct, A/C on, 65 mph mostly, 4 people plus full luggage, all stock except for tires. Strangely or coincidentally, the displayed value was right on, which may mean that it was 6% overoptimistic -or more unlikely that this tire size calibration works, assuming I even used it.
------------
Care to help us figure this out so we know how accurate these things are?
Last edited:
