EPA MPG Estimates

Hi All,

The Prius is the only car I have ever gotten near the old EPA rating with year round. In the summer at 80 - 85 F temps, I get right at the 55 mph combined for the mostly highway mixed suburban commute. On weeks without AC in the summer, the car gets in the high 50's, and one time better than 60 mpg. I set the cruise control at 63 mph usually, but not for long, as the traffic is such that I am in slow and go for about 1/4 th of the highway distance. In the -10 to 5 degree starting temps period (parked outside) with lots of snow we have had recently the Prius did 42 for the last tank. But that was with some bad traffic right at startup of some of the coldest days on the drive home. In 10 degree F morning temp weather it did 46 mpg. Since refueling on Sunday, with some mild temps the tank average has been 51.3 (was at 52.0 when I got home wednesday). That was with near freezing starting temps, and one below freezing drive home (today), and a couple of days at 45 F for the drive home.

My old Saturn SL2 would get about 28 in summer 80 to 85 F conditions. And this was with my AC-off -accellerate, and AC-on-to-brake into the traffic flow technique (versus the Prius set-and-forget). A little cooler (60 to 70 F), when I did not have to use the AC, it would get 30 if there was no slow-and-go traffic for the whole week, which rarely happened (maybe 3 weeks out of the 5 years I owned it). In the 10 degree F starting temp winter weather it got 25 mpg. During the 5 years I had it we did not have any weather as cold as the previous month. Of course, there were exceptions when there were 5 days of stop and go driving, and the poor thing was lucky to get 20 mpg.

So, even in freezing weather the Prius is better (51.3 mpg) than these new EPA estimates (46 mpg), whereas the 2000 SL2 automatic is right at the 26 MPG new EPA average. I am using the same tire brand and type, of the same size on the Prius as I had on the Saturn. My experience is the EPA test is about 11 % too low for Hybrid mileage, and dead on for DOHC automatic transmission cars. EPA is reporting that some drivers do get 60 mpg on their site however:

http://www.fueleconomy.gov/feg/calculatorS...amp;model=Prius

Why does the Prius do better in relation to the EPA values here in suburban Chicagoland? I think it has to do with the interferance-limited driving we have to do, also that the Prius recovers energy downhill, that is not measured on a dynamometer, and that the hills here are small which tends to put the engine in a more efficient loading at cruising traffic speeds, and the hybrid battery is big enough not to become over charged on the small downhill runs.

 

<div class='quotetop'>QUOTE(Tom 6850 @ Feb 23 2007, 06:57 AM) [snapback]395093[/snapback]</div>

I also now beat the combined estimate (I achieve 48.5 mpg overall).

My highway driving is affected by topography. Travel in to work is about 45 - 48 MPG, and the travel home is higher; I end up a rount trip at about 50 MPG. This is all (98 %) highway driving at 65 MPG, cruise control set.

And in town, I just do not get the performance other drivers achieve, I get the low 40's mpg. I think this is because trips are short, it only takes 15 or 20 minutes to get anywhere I go in town, so the car does not really warm up.

I might decide to increase the tire pressure; I got Michelin hydroedge from Costco, but they set the pressure at something like 38/35. I know some people suggest a stiffer tire.

 

When the temperature outside is about 20F is when I average about 46 MPG. So I'll be exceeding EPA estimates about 9 months out of the year.

 

The recent vehicles I have experience with--a 98 Cadillac Concourse (now DTS), an 02 Dodge Ram truck and an 06 Honda Odyssey, all have gotten about the advertised mileage on the highway as long as speeds did not exceed 72 MPH. 51 MPG is probably reasonable for a Prius as well. The trouble with city driving is that everyone has a different definition of what city driving is. I think the new ratings will be good for the Prius--it is still the best mileage performer out there! With the 60 MPG rating, many jumped in the car and expected to get 60 MPG driving like they always did--and most here will admit 60 MPG is hard to obtain, and getting close requires extraordinary driving techniques. Any car will respond to conservative driving techniques, but the Prius will privide better results due to the design. Now I want Toyota to hurry up with the next-gen Prius!

 

Why does the Prius do better in relation to the EPA values here in suburban Chicagoland? I think it has to do with the interferance-limited driving we have to do, also that the Prius recovers energy downhill, that is not measured on a dynamometer, and that the hills here are small which tends to put the engine in a more efficient loading at cruising traffic speeds, and the hybrid battery is big enough not to become over charged on the small downhill runs.
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I'll second that. The Prius is the perfect Chicagoland commuter car.
-Prius driver who commutes up and down the Fox River Valley in the Western burbs.

 

<div class='quotetop'>QUOTE(Per @ Feb 23 2007, 08:30 PM) [snapback]395600[/snapback]</div>

Agreed. With my past vehicles, it was easy to meet or beat the EPA. With the Prius, I have only beaten the EPA under exceptional circumstances (although my short commute doesn't help, but I also have rolling hills on a road with traffic flow at 30-40 mph so that balances it out). Now that I have over 8K miles on the vehicle I expect next summer to be better, but still, it's the first couple months that people want results.

If you look at GreenHybrids or EVWorld ratings, actual reported mileages are about 45-50 mpg, which is what the new EPA ratings are. It will be a little hard on the pride to transition to those numbers, but better for us overall. This will bring it inline with expectations. Plus, the next gen Prius will have better mpg ratings, so it should be back up to around the current ratings, but this time achievable by the average car buyer, and will be that much more impressive to the general public.

 

<div class='quotetop'>QUOTE(efusco @ Feb 23 2007, 08:49 PM) [snapback]395554[/snapback]</div>

Without downward adjustments for car pool lane stickers, the Prius & Insight will be the only qualifying cars. Ohhhh I feel a new level of smugness coming on B)

 

<div class='quotetop'>QUOTE(qbee42 @ Feb 23 2007, 12:11 PM) [snapback]395237[/snapback]</div>

<div class='quotetop'>QUOTE(efusco @ Feb 23 2007, 12:21 PM) [snapback]395247[/snapback]</div>

Yep sounds low! I just returned from a wet and wild ride to Sacramento (115 mi 230 mi rt), 50 F, 42/40 cruise at 68 when possible: 54 mpg there and 47 for roundtrip. My first 7 miles for 30 minutes was spent simply leaving the city when I hit the Bay Bridge I was at 72 mpg on a new tank, LOL.

It was interesting to put in the vehicle we used to have, Grand Cherokee, 12/15 new EPA ... Yep that was our experience.

 

<div class='quotetop'>QUOTE(paprius4030 @ Feb 23 2007, 12:53 PM) [snapback]395223[/snapback]</div>

All flex fuel cars use dramatically more fuel when burning E85- that's not news. Ethanol has much less energy in it per gallon. That doesn't mean that you're using more energy when you're using E85, though, it just means you have to refill more often because the fuel is "bulkier" for how much energy it carries. (Now getting ethanol from corn hasn't proved all that much of an energy savings because of the energy inputs required to make the fuel, but that's going to improve in time as they start switching to cellulose feedstock in place of corn.)

Conversely, diesel fuel has more energy per gallon than gasoline (about 20%). Part of why diesel vehicles get more miles per gallon than their gasoline counterparts (for example, in 3/4 ton pickups) is because the diesel engine is actually more efficient... that's actual fuel economy... but quite a bit of the MPG difference is in the fact that there's more energy in that gallon of diesel fuel than there is in the gallon of gasoline. So as we start to broaden our horizons with respect to vehicle fuels we are going to have to start thinking about how many miles we go on a unit of energy (say 100,000 BTU) and stop focusing so much on miles per gallon. Gallon of what? You can't measure hydrogen or electricity in gallons at all.

If you think ethanol is bulky you should see vehicles rigged up to run on compressed natural gas. Those tanks are HUGE- take up almost the entire trunk in the natural gas Civic, for example- and you get a real-world driving range of 250 miles tops (for fear of running out, since you can't fill up on any street corner with one of those). But for that huge tank you only store the *energy* equivalent of maybe 8 gallons of gas.