I have a few technical questions related to Prius MPG

Yes. Each generation has been more aerodynamic. Each generation has fewer belts and more electric powered accessories. Each generation has more computerized capabilities. Considerable effort has been made to get the Gas engine to warm up quickly, a cold engine is an inefficient engine. The batteries are made more reliable. Tires are reducing their rolling resistance.

The Prius v is much larger, so is not as fuel efficient, the Prius c is much smaller, but less aerodynamic and designed for lower cost. The Prius PHV is a much more costly vehicle.

The Gen 1 Prius was sold in the US Model Year 2001 - 2003. 41 MPG (Combined, I am using Combined for all)
Toyota Prius (XW10) - Wikipedia, the free encyclopedia

The Gen 2 Prius was MY2004 to 2009 46 MPG
Toyota Prius (XW20) - Wikipedia, the free encyclopedia

The Gen 3 Prius MY2010 to date 50 MPG
Toyota Prius - Wikipedia, the free encyclopedia

The Prius v is new this year 42 MPG
Toyota Prius v - Wikipedia, the free encyclopedia

The Prius c is new this year 50 MPG
Toyota Prius c - Wikipedia, the free encyclopedia

The Prius PHV is new this year and gets 95 MPGe in electric mode and 50 MPG in Hybrid mode
Toyota Prius Plug-in Hybrid - Wikipedia, the free encyclopedia

With the exception of the PHV, this is wrong. It always costs you to convert energy from one form to another, Only in the PHV does some energy start as electricity, in all other Prius, it always starts as gasoline and would suffer conversion losses making it electricity. In the other Prius models I would advise against ever using the EV mode if you want fuel efficiency.

The PHV can be all electric to 62 MPH, most other Prius must run the gas engine at speeds that vary from 41 to 45 MPH.

The Prius c does NOT get a better EPA rating than the Prius Liftback. Both are rated at 50 MPG Combined.
Smaller cars are hard to make as aerodynamic as larger cars, so the highway mileage is less than the Liftback, perhaps why Toyota calls it a City car. The C gets a smaller High Voltage battery so the engine needs to do more of the work, it is cheaper, so Toyota must have cut corners to curb costs.

That would be the Prius PHV.

 

It's interesting, though, to compare the Fuelly reports for the Liftback and the Prius c. To my eye, the C's bell curve is a couple of MPG to the right of the Liftback's., but it probably needs a larger number of reports for the C in order to be statistically meaningful.

 

I considered using Fuelly numbers, but decided EPA was the reproducible figure.

If we assume the EPA numbers are right and that Toyota's marketing works, then more C owners should be driving in the City while more Liftback owners are driving on the Highway, so the curves will not represent the same kind of driving. (The number of PriusChatters who seem to have purchased the C for Highway use hints that Toyota is doing a poor job marketing the C and the Liftback)

It is also possible Toyota 'sandbagged' the C's EPA numbers, so not to lose Liftback sales, then the Fuelly numbers would be more right than EPA.

Sandbagging - Wikipedia, the free encyclopedia

 

All good points. However, my C has been used mostly for highway driving, and I'm averaging just over 50MPG on Fuelly.

 

I would just add the best mpg for the money also depends on your driving style. The C and the Gen I are both excellent "city" cars but the Gen I fuel economy suffers more in cold weather than the C. The Gen I is/was rated at 46hwy/52 city and I have verified (on mumerous occasions) that it does indeed easily get 52 city once the ICE is warmed up. The C seems to get closer to 60 city once warmed up. I know there have been numerous small upgrades to the Prius but the resulting mpg improvement is relatively small.

Gen 1 (46 hwy/52 city)
Gen 2 (45 hwy/48 city)
Gen 3 (48 hwy/51 city)
C (46 hwy/53 city)
V (40 hwy/44 city)

I think the EPA numbers for the gen I were revised but, like I said, I regularly achieve 52 in the city in my Gen I (in the summer of course, AC/climate control not in use).

 

Prius Plug-in currently averages 77 MPG on Fuelly, with some owners averaging over 95 MPG. Mileage in the PiP model varies widely depending upon miles driven per day. If you typically drive only ten to twenty miles per day (or per charge), your mileage will go through the roof. I drive about 85 miles a day on busy freeway and average 68 MPG.

 

I am getting 116 MPG on this tank. Note, that figure ignores the electricity input. Just replying in regards to how fuelly tracks MPG.

 

Welcome, Going Green. You have fair & valid questions.

What is significant? 1mpg out of 50mpg is 2%. There are so many variables that affect fuel economy it is tough to pin down specific causes.

If you are looking for the most fuel efficient production car built then you want a 2000-2006 Honda Insight. It is an aluminum bodied compact so it isn't ideal for everyone's lifestyle. Experienced drivers can get 75-125mpg over the same route that a Gen2 Prius delivers in the 50's-60's.

If you want the most fuel efficient car in production today then you'll want to look at the EVs. If range (or price) is an issue then you need to step down to the plug-ins, Prius & Volt.

Check out the Prius v, c, liftback, and plug in to see which fits your needs best. Does it really matter if you can get the best fuel economy in a Prius c if it can't haul all your stuff?

Every car has its own plusses & minuses and they are different for different owners.