2003 Prius (also called Gen I): 507 mi / 73.8 MPG = 6.87 gallons true (~5 gallons still in tank) 105.2% * 507 mi = 533.4 miles true 533.4 / 6.87 = 77.6 MPG true 105.2% is GPS measured, calibration constant for these well worn tires. I plan to post an update after replacing the well worn, Sumitomo T4s with Yokohamas. I'll measure the new tire calibration constant and repeat the test for a longer run. Bob Wilson
It never came to mind that I should check my odometer against a gps and come up with a correction for the distance on my trip meter. I run 50 psi and it makes me wonder it I actually am getting better mpg than indicated by my calculations at the pump.
If you are running OEM tire size (revolutions per mile) your actual MPG will be worse than your displayed MPG. Going one size larger diameter tire often makes it more accurate if not completely so and you'd have to go two sizes larger diameter to get across to inaccurate the other direction. For the vast majority of us even with high tire pressure we are getting worse MPG than the pictures indicate.
The biggest problem I encountered is letting the GPS settle once it turns on which appears to take a minute or two. Thereafter, there is a slight lag but I've not found a big error compared to other sources. Bob Wilson
so if I get going with my gps and then set my trip meter and drive like 100 miles I should get an accurate correction factor?
only if your route is entirely on a salt flat in Utah. Any 3D component of the trip will distort the mileage vs the overhead view. (I'm assuming you are using a GPS that doesn't track 3D paths and instead just gives long/lat coordinates, let me know if common GPS units do 3D path logs now).
Good point! I'm using a Garmin nuvi and my calibration runs are on fairly flat areas. Fortunately, the Garmin trip log includes the altitude so I can load it into a spreadsheet. However, the altitude changes, ~80 ft, and low frequency, are so much less than the x-y distance traveled, 50 mi or 264,000 ft., it isn't clear solving the x-y-z geometry would be significant. Bob Wilson
my drive to work http://priuschat.com/attachments/elevation-route-png.44545/ I don't think there is any route I could pick in my state that would be worthy of ignoring the 3rd dimension.
I'd like to update my entry on the list please. There will (at least briefly) be 3 of us at 81.1 mpg. I'm so vain I ran the battery low to reach 81.2 but - cheaters never prosper - the ICE kicked in before I could take this picture. This was P&G on (mostly) two slow round trips with ~1200' elevation change, with <30 miles of highway and just a little AC. (I should have used more - where's the "sweaty" emoticon?) Fuel was 87 octane, E10, RFG in Mass.
The x and y axis scales are off by about 10*3 which gives an inflated impression of vertical distance travelled. Bob Wilson
yeah non zero axis strikes again, I'd love to have an easy way to get that graph with an axis of my choosing. Still the text might give is a clue ascent 549 ft descent 630 ft total distance 14.77 miles 549+630=1179 ft or 0.223295 miles which is about 1.5% of the length of the 2D trip distance or enough to skew the odometer reading by about as much as changing to one size smaller or larger tire. I suppose there are parts of the world were that difference would be less noticeable, I just don't trust any method that doesn't at least try to negate issues like that.
Well yes, this is PriusChat and I and folks like me hang out here. I am hoping we're on the same page about accuracy. <GRINS> Bob Wilson
Doh! I was working on a good tank, had a 70 MPG trip home the other day. Next day my average dropped noticeably. Continued to drop, let my car sit for a couple of days and checked my tire pressure and one tire was down to ~10 PSI (no telling how inaccurate that reading is as the accuracy of a tire gauge is only for the middle 40% of the range and I don't have any 20 PSI max tire gauges laying around). The sidewall was pretty soft and adding air seemed to firm it up. Even at ~10 PSI I couldn't visually tell the tire was that low. These modern Michelin tires keep their shape well even when vastly under inflated. So this tank is on hold, I had to drive another vehicle to work. I haven't had time to pull the wheel off and look for the puncture or determine if it is a manufacturing defect. After I do, I'm going to toss it in the pickup truck and drive it down to the tire shop to get it patched/replaced. I hope it's patchable as I only got the tires about 7,000 miles ago. edit: 300+ miles into the tank and I'm at 60 MPG, still on pace to beat my old tank from Dec 2012. Glad to know that my HV battery from 10 years ago is still in good enough shape to keep the MPG going.
