Another where'd my MPG go thread...

You have a G3-III (base)---right?

Check your vehicle speed with a GPS.
Your new P195/65R15's aren't the same diameter as the (worn) tires that they replaced, since you ground down enough of your old tires to throw your VSS (and your mileage calcuguessing) off by about 4-percent---or about 3-MPH at 65.
Add the higher rolling resistances of tires that actually have a tread, and some other factors (wheel covers) all of which are additive, and you'll probably find that you really weren't getting as many miles per tank from your previous tires as you thought you were.
Since it's too late to verify the differences between old and new---unless you have a friend with similarly bald tires, you're just going to have to be satisfied with the MPG that you're getting now---with street legal rubber.

Good Luck!

 

Yes I am....or at least they can.

Most cars have a VSS (Vehicle Speed Sensor) input on the drive train somewhere. Typically these are a magnet affair that produce pulses that are read by the ECU, converting the same into MPH.
When you grind down your tires, it reduces their size. They have to go roundy-roundy more times to cover the same mile as when your tire had treads, and this will produce more pulses for your VSS input. So....your car thinks it's going further than it really is....or faster, depending on how you look at it.
Lotsa things will cause the amount to vary---including what you consider to be a worn tire. Typically you'll lose 3MPH on a set of worn out tires, again depending on size and wear.
Most car manufacturers have bottom-feeding, slimy attorneys that encourage them to factor this into the speedometer/odometer calibrations, and they happily comply, since it knocks a couple percent off of their warranty liability in addition to protecting them from being sued for speedometer error---even though tire wear will result in your speed being less than advertised.
I don't know how Priuses calcuguess VSS---and given their tendency to over engineer everything else in this car (except the oil filter access panel! ) I really don't want to know, but you may rest well assured that your speedometer will be affected by tire circumference.
If your speedo is off.....your odometer is too....and your MPG's will also be (albeit slightly) affected.....unless Toyota uses a VSS that's independent of the drive train, like Doppler radar or GPS.

You never know.....

 

Weather?

Has the weather been any "different" over the last couple of tanks? Wetter? Windier? Hotter (A/C type of hot)?

 

I am new to prius family, but i will never drive my car over 3k with out oil change. With prius engine is barely working, i'm gonna do it every 4k, may be.
c

 

Those 40/50s in the morning are a killer. We don't have quite those same fluctuations up here, but 40s can still give you a 3 MPG or so hit just on their own, esp with shorter commutes. We've been 50s/60s low and 70s/80s high here for a couple weeks. Of course, we went from 7 days of sun shiny days, to 7 days of cloudy, stormy, rainy days.

Not sure if it was mentioned, but tires also have a break-in period and some are worse than others during this time. With your last 3 tanks going up, I think you'll have it back up in no time. Probably 2 or 3 more tanks to go, and you'll probably be done the break-in period.

 

Complete waste of resources to change out conventional oil every 3k miles unless you were in very harsh conditions.

Your Prius has full synthetic or maybe synthetic blend oil. Changing it out at 4k is too early IMO.

also, at the Honda workshop they warned not to change out oil early on a new engine as there is something in the oil to aid break in.

Best to go with manufacturers recommendation unless one claims to have more engineering knowledge than they have which is impossible.

 

Differences in mileage due to tire size (worn):

Radius of stock tire ~ 12,25"
Radius of dead tire (no tread) ~ 11.92"
Circumference of the stock tire ~ 76.97"
Circumference after tread is gone ~ 74.90"

Moving from dead tire to new with these figures causes a 2.77% decrease in mileage.........

 

The same basic thing has happened to me about the last of april 2011 to make a long story short ,the goodyear integritys in the front got flat spots on them at about 15000 miles when the dealer rotated them to the rear the noise was bad, goodyear dealer said the front was out of line finally dealer puts on a set of yokohamas p195/65//r15 89t advid trz this is a201o prius by the way. before the change we were getting 44-46 and once i saw 52 mpg, after the change driving home 39 mpg ,in town 35 36 mpg . i hope its getting better today 5/18/11 we saw 43 44 mpg on the tripto the dealer to check the speed o they say toyota says anything under 5 mph is in tolorance ours is 3 mph slow.
our dealer has a program called tires for life as long as you service the car there. im real quick now to realize that i have no choice as to what they put on. if they say to use the correct replacement parts shouldnt tires also count? as these yokos are not l r r tires.
this leaves me with a bunch of questions
the dealer says the integritys have major problems and wont install them i called a tire store about michelin energy savers and their supplier says the have stopped making them because of problems so what l l r tire is best to use?
i am thinking of a better looking wheel stock deminsions only what does a stock wheel weigh? may be
can i find a tire size that will compensate for this 3 mph slow speed o and bring the mpg back up? and be sure of the change
dealer says that the computer will relearn this tire non l l r tire i just think that statement is a bunch of bull?

 

===
Tire pressure can signficantly effect your MPG so you
need to check your tire pressure settings.
Toyota's official spec setting is 35 psi for the front tires
and 33 psi for the rear tires
To get the lowest rolling resistance for a tire - the
tire pressure must be set to its highest cold maximum
tire pressure ( found on the sidewall of the tire).
For most tires including the OEM Yokohama Avid S33
the max cold tire pressure setting is 44 psi. Many
serious Hypermilers go slightly over this and
set their front tire pressures to 50 psi.
==
The Prius MPG improves as the outside temperature
goes over 60 degrees fahrenheit AND when the road
is either flat or generally going downhill AND when
it is driven for longer than 30 minutes/7 miles at any
given route AND if the Prius is driven under 45 mph
AND if the Prius is driven at a constant speed and
does not have to stop.
==

Walter Lee
hypermiler neophyte
2010 Toyota Prius III, Blue Ribbon/Dark Grey, oem floormats
Yokohama Avid S33 (front psi 48 , rear psi 44)
No grill blocking
Scangauge II (AVG, MPG, SoC, GPH)
odeo +12000 miles, +58 mpg overall
best tank 66 mpg (calculated at the pump, 598 miles 4/19/2011)
worst tank 52 mpg (calculated at the pump, 428 miles, 12/27/2010)