So, I was a bit bored in the passenger seat of the xB on the way back from Bellevue last weeked. (Wife needed to drive - she's 33 weeks pregnant and can get a bit queasy if she's not driving.) Just south of Olympia, there's an odometer test. So, I flipped the odometer over to Trip A and did the test.

Boy was I surprised... the car's odometer is showing around 1.92 miles traveled for every 2 miles on the road. (that's a bit of an estimate, but it's slightly more than 1.9 miles)

I was wondering why I was only getting 29 mpg or so. Now I know that it's actually 4% better than that...

4% seems to be a rather large discrepency to me. Anyone else seeing something like this?

 

My 2005 xB's odometer also reads 4% low, which is to our advantage as owners. No, the speedometer does NOT read low.

 

Common to all xB model years and discussed many times here on ScionLife.

The speedometer is about the same amount off in the OTHER direction.

 

The JDM bB uses 185 65 15 tires. Our stock sized tires are a bit smaller which could be the culprit . Am I just talking jibberish?

 

Moving to 185/65R15 tires will correct the xB's speedo error, but will make the odo error about 3.1% worse.

How do i know?





Tom

 

Good info... Now can we compensate with tire size to correct the spdeedo and odo errors? If so, what would be the optimal size?

 

If you attempt to make corrections via tire diameter changes, if you get the speedo right on, you've made the odo worse, if you get the odo right on, you get the speedo worse. Factory tire size sort of averages out the errors - about 3% for each. (My current setup is accurate speedo and 6.1% error for the odo.)

 

My odo is 4.3% off. I checked it on a long trip with a gps. I just adjust the mileage every time I fill up so I always know how much I am really getting. Makes a world of diff.
upshift

 

So what is the real MPG you're getting?

I have no idea how you guys can calculate all that!
How good or bad would my readings be if I ran
215/45/17

 

The only way to *know* with any chance of accuracy is to start watching mile-markers on the side of the highway.

See a marker and hit reset on one of the trip counters as the front of your car passes the marker.

Keep track of the markers (a lot easier if you have a navigator to do this for you) and after you have passed 20 or 30 of them, compare what your trip odo says as opposed to how many actual miles you have gone.

The longer stretch of more or less straight highway you can do this on the more accuracy you will have. An alternative is to do an equivalent using a GPS unit.

Once you know your error you can correct your MPG from 'indicated' to 'actual.'

For me I'm close enough by multiplying the indicated milage at fill-ups by 1.06.