google earth
 

Google earth lets you pre-measure a very specific route, and then go out and drive it to make the comparison.

In the google earth program, just zoom in on the area you want to measure, go to the "tools" menu, then to "measure", then select whether you want to measure a "line" or "path". ("path" is more useful unless the road you're measuring is perfectly straight!)

I decided to try this with
 

I decided to try this with my car so I checked the route I usually use and Google said it was 39.76 miles. When I used this route, my odometer measured 38.7 miles. This shows that I need to add 2.75% to my odometer. My mileage would have been 50.85mpg. With the correction, it came to 52.25mpg; a significant difference indeed. Thanks for the great idea MetroMPG.

OK, I was a little skeptical
 

OK, I was a little skeptical that this would work. But I tried it anyway. The SuperMid on the Prius said 41.04 km to work. After calibrating the SuperMID on the Del Sol, the trip distance is 41.04 +/- 0.05 km when I don't use ignition off coasting, and about 40.50 when i do use ignition off.

Google earth said 41.04169 km. You don't get any more calbrated than that! Dead on! :-)

GPS
 

I use my portable GPS unit to verify speed and distance -- most speedometers are off (when my Integra shows 61, I'm actually going 57 -- the Camry I tested was off similarly). I rented a Focus once that actually went faster than the speedo read -- could get you in trouble. Satellites are cool.

RH77

Re: GPS
 

I also use my GPS unit to calibrate my speedo. I've yet to figure out however how to test the distance travelled.

krousdb wrote:Google earth
 

i hadn't tested it myself beyond the short 9.7 km route i did yesterday.

glad to hear it's accurate on longer paths. cool stuff.

thanks, beta testers!

I used to have google earth
 

I used to have google earth a couple of months back, but I didn't know you could use it to get better mpg distances. I'll give it a try.

distance
 

Your gps should have a trip distance screen that tells how far you have traveled - you should also be able to reset it. You may also have tracking that records your travels into the gps that can be read out into a computer. I have been saving tracks for years from everywhere I go - cool to see the roads you took on a trip by overlaying it on a map on the computer - also good to keep track of how far you traveled and when.

I'm going to see what my car
 

I'm going to see what my car says for a street I'm driving to. I plotted a course on google earth right from my parking space to a street I know it said 1.62miles. I'm thinking my odometer will say 1.7

We will see.

went out this morning with
 

went out this morning with an ambitious plan to both (a) practice engine-off driving with the new switch, and, (b) drive a longer route that i could also use to also check my odo accuracy against google earth.

long story short: screwed up part (b).

i made the route too convoluted (i was doing "laps" on some suburban and exurban roads around the edge of town). but i stupidly altered the course each lap, so sometimes i went CW and other times CCW, cutting through the middle of the course to switch over, etc. etc. and in the end, my chicken scratch "log" of my turns was useless. and i'd retraced my steps so often, i couldn't really remember my path.

doh! i'll have to stop trying to walk and chew gum at the same time.

on the plus side, the scangauge reported 68.1 mpg (US) (!!! :-O ) over the course of the drive. i was actually a little over 70 mpg on the leg back to the house, but i got hit by 3 red lights in a row, and a train crossing at the bottom of my longest hill!

the s.g. registered 18.7 miles (30.0947 km). my odometer registered 30.5 km (18.95 mi). 23 mph avg speed / 42 mph max; rain, wet roads; 6 C / 46 F ambient; 1.25 hrs EBH.

i'll have to go out some other time i'm planning a less circuitous route and try the google earth thing again. i'm curious to see which is closer to reality, the odometer or the scangauge.

it's rare that i go out driving with the sole purpose of seeing what kind of mileage i can get, but this new ignition switch combined with the uninterrupted readout on the scangauge has boosted my FE into a higher orbit. fun!