New Prius - only 39mpg?

I purchased my 2007 Touring Prius in August 2010, and since then have never reached or beat 39 MPG. I have a mixed set of driving conditions, city (0-40) and freeway (80 MPH, but don't tell the CHP!) and weather (for Southern CA, that means lots of sunny days and, this year, more rainy days than usual.

I get really annoyed when I pass the billboard (on the 105 freeway in LA) that boasts "Prius 50 MPG"

What gives; how can I get better mileage results?

Thanks...Chris in SoCal

 

Don't get annoyed, Chris, you can likely improve that. Since it's a common question, read up below. Trying a couple things will help you out.

http://priuschat.com/forums/knowled...ussion/37214-why-don-t-i-get-epa-mileage.html

 

Higher speeds have a huge impact on fuel economy, running at 80mph vs 60 mph consumes 50% more energy just overcoming drag from the wind. Weather's humid too in LA so that doesn't help.

Unfortunately, like the OP you are also from LA so driving at 60's not a viable option.

 

Besides, the above, one should read http://priuschat.com/forums/other-c...uth-about-epa-city-highway-mpg-estimates.html. Hint: The tests aren't done on a real road nor do they measure actual fuel consumption. The average speeds of the fastest portions of the test are no more than 48.4 mph.

If one really wants mileage help, please start a new thread in the 2nd gen fuel economy section answering http://priuschat.com/forums/gen-ii-...-answer-these-questions-esp-if-youre-new.html. Chris, you have a 2nd gen, not a 3rd gen. Per Side-by-Side Comparison, by current EPA test (after adjustment by formula), combined mileage is 46 mpg.

CR at Most fuel-efficient cars rated the touring Prius at 42 mpg overall .

From everything I've read, the only numbers automakers can legally advertise are those from EPA tests results at which the 3rd gen Prius does get 50 mpg combined.

 

Like others have said, you definitely have to back off that 80MPH freeway driving as well as smooth out starts/stops. I guessing you jackrabbit start and probably brake too hard at red lights and stops. I'm just assuming since you say you do 80mph.

 

the bill board is for the 2011, think how much money you saved. makes up for the mpg difference.

 

Just picked up new 2011 and am still on first tank from the dealer:

Performed a little test yesterday. With engine warmed up, reset the "B" trip, drove home from the barn (country road, 5.1 mi) and registered 61.8 mpg.
Then this morning from a cold start (overnight 55 deg), reset "B" trip and drove 3.1 mi stop and go in town, and registered 39.4 mpg. Not too scientific, but gives one an idea of what you can see.
I always keep "A" trip to give me mpg and miles between fillups (normally between 9.5 and 10.5 gallons). Most of my dailly trips are between 5 and 15 miles. I Keep the tires at recommended levels.

 

NE Atlanta area is very hilly and probably about 60% as road-ragey as LA so I can kind of feel where you are coming from.

We get from 40-48mpg (winter to summer) and I am happy with it because I have to routinely go into the power band to climb hills, avoid idiots and the like. The biggest thing I do to save gas is gliding to lights...so silly to accelerate just to brake.

As for not wanting to change your driving style...it just happens, like it or not you start driving more efficiently.

The good news is it will translate to all cars, we are getting 4 more MPG than EPA on our Fiesta because we are both used to driving the Prius.

 

One key note here is that what a lot of of assume is average speed is actually too high. At least this was the case with me.

If I commute 56miles (95% freeway, 5% city street) at 65mph with cruise control on, my Scanguage says I AVERAGE 55-57mph for the entire trip. When I did the same test from Davis to LA I drove between 80mph-85mph most of the way and my AVERAGE speed was 77mph. So it's a good idea to think about the short sections of your trip where you are driving through the city or your neighborhood at 25-35mph. That really puts a dent in your AVERAGE mph. My point here is while the EPA tests AVERAGE mph seems rather low, it is not quite as low as you think it is. Just because you drive 75mph on the freeway for 2 hours doesn't mean your average speed is 75mph.

 

I am lucky to get above 26mph as my average with daily driving.

 

Keep in mind that average speed is very misleading when it comes to fuel mileage. This is because of the non-linear relationship between speed and drag. The power required to overcome aerodynamic drag is proportional to the cube of the speed. The energy expended is power * time.

To see what this does to mileage, let's look at an example where we average speed as a function of time. Let's say we drive one unit of time at 20 mph and another unit of time at 80 mph. Our average speed in relation to time is (20 + 80)/2 = 50 mph. Now let's compare the amount of energy required as compared to driving two units of time at the average speed:

For simplicity we are going to ignore actual energy units. Our results can be scaled to get any desired energy units simply by multiplying by the appropriate factor.

For our first run of one unit at 20 mph and one unit at 80 mph:

Energy = 20^3 + 80^3 = 520,000

Now for two units at the average speed of 50 mph:

Energy = 2 * 50^3 = 125,000

You can see that the results aren't even close.

We can also do average speed as a function of miles driven. In this case the numbers are closer, since you speed less time at high speed, but the non-linear relationship still holds. From a mileage standpoint, driving at high speed and low speed is not the same as driving at the average speed.

Tom

 

Jerk!

 

Prius still double the MPG of a non-hybrid for the short trips. Prius PHV would be ideal for you though.

 

Don't forget that distance traveled in time is proportional to speed, so MPG only varies quadratically (the power of 2).

 

Yes.

Energy spent overcoming wind drag varies quadratically.

 

Oh yeah, you put it more accurately than i did.

MPG actually varies by the inverse square (not counting other losses), since I forgot it is the reciprocal.

I feel that the SI method (fuel consumed divided by distance) is actually easier to use and conceptualize.

 

I purchased my Prius almost two weeks ago, and was disappointed that the Trip A calculation over 150 miles was "only" 42 MPG. After reading this forum, I discovered a thread on tire pressure. I immediately went to the service station, and discovered that my tires were each at 32psi from the dealer. I upped them to 40 front, 38 rear. I then reset the Trip B odometer. Over the next 50 miles, I am now showing 56 MPG. Ride is a little harder, but I can get used to it. Just hope it is safe on wet roads.

 

If you mean safe from hydroplaning, the aviation and NASA links in other threads find that higher pressures are more resistant to hydroplaning. Your 25% boost in front should push hydroplaning onset speed up by not quite 12%.