Poor MPG

[Texasota]

Stopwatch and roadside markers. When they match to GPS and roadside cameras, you can have a safe bet their accurate. My Speedo reads 62 MPH when actual is 60.

I don't know if it makes a measurable difference or not, but it seems like worn tires (reduced circumference) will result in the speedometer and odometer reporting inflated numbers.

[Texasota]

I have not attempted to measure odometer discrepancy yet but I have confirmed that the speedometer reads 1 MPH faster than the true speed (confirmed by my GPS and roadside speed camera).

HB, thinking about this some more I'm confused about why odometer error is a factor when comparing the MPG as reported by the trip computer to my hand calculations.

 

My hand calculation is based on the gallons added to the gas tank and the miles traveled as reported by the car's odometer. Doesn’t the trip computer also use the car's odometer for its calculation? If so, then both would have the same odometer error built into the calculation which makes the relative difference between the two accurate? Hope this makes sense what I am trying to say.

[tr7driver]

When I set my cruse control for 70 mph 70 appears on the display but my speedometer looks more like 68 or 69.

[md13ffhguy]

^^^ Precisely! Or imprecisely! We have to assume that there's some amount of error in most measurements. I assume the odometer is consistent, if not accurate, although tire wear and inflation introduces variance, but I don't feel the need to try and account for it. I think the variable we know the least about is measurement of gasoline pumped and used.

 

So, I just assume my manual calculations are "correct." In the end, what really matters to me is the dollars I've spent to cover my travels.

 

EDIT: tr7driver posted before I clicked Submit, so my ^^^ refers to the post above by Texasota.

Edited October 13, 2014 by md13ffhguy

[acdii]

My trip 1 was never reset from the day it left the factory. It is off by a few 10ths compared to the odometer. It varies too.

[MXGOLF]

It does look like the ones with good mileage are in warmer, flatter climates. The gas does make a difference also. Crappy gas won't help get good mileage. 13,000 miles and mine is at 37 lifetime. Bad gas, colder weather and hills in Oregon are part of the problem. I have been putting in non ethanol gas in for the last 10 tanks and it has helped somewhat. Got a few tanks between 43 and 44 mpg. Still not what I had envisioned when I purchased and people are getting 50+ mpg.