You will not get 50 MPG if...

[afstudio]

I purchased my 2010 Prius about 2 months ago and I'm averaging only about 40mpg. I drive 5 miles to work (mostly uphill) but I've put 800 miles on the car and the mile is the same. Do I need to get it checked out?

Andrew, San Rafael CA

Originally Posted by wfolta

None of this means you're a bad person. It's just meant to give some thoughts on why you might not be getting EPA mileage (or better) in your driving. As the ads say, YMMV, and even if you don't achieve EPA, you're probably getting better mileage -- for the same geography, climate, weather, and driving style/habits -- than any other car you might choose. For your consideration, you probably won't get 50 MPG if...

1a. You drive 5 miles to work. The car gets relatively low mileage while warming up, so you take a big mileage hit at the start of every trip, and need to run long enough to overcome that initial deficit.

How far do you have to drive to get 50 MPG? As one example, I drive 11 miles to work in a mixture of city, open highway, and stop-n-go backed up highway, and get 50 MPG without much trouble.

1b. You drive a bit farther than 1a, but you "warm up" the car for several minutes before driving. ("Warming up" is getting 0 MPG, and it doesn't help the car.)

1c. You drive a bit farther than 1a, but you drive the car hard while it's warming up. (The engine's not getting great mileage anyhow, plus the car will use maximal electric power to keep down the strain on the cold engine, further wasting energy.)

2a. You stick like glue to the car in front of you, and don't let anyone beat you coming off of a traffic light. If you spend a lot of time in the red "PWR" acceleration zone and brake hard, you'll get poor mileage. Better than you would have if you drove like this in another car, but not 50 MPG.

2b. You either don't look at traffic ahead, or you do so only to note in the back of your mind that you're going to have to stop up where the red lights are all on. You don't need to leave huge gaps ahead of you, but if you find yourself accelerating towards a car that's stopped/slowing in front of you, you won't get good mileage.

2c. You never coast. You're either on the gas or on the brakes.

2d. You spend a lot of time going 75+ MPH.

2e. You think that Cruise Control gets better mileage than a human driver. (CC only saves gas to the extent that it keeps you from going 75+ MPH. Otherwise, it makes stupid choices.)

3a. It's winter, or you drive in cold, rainy/snowy weather a lot. (Longer engine warmup, precipitation on the road slowing you.) Or it's summer and you live where it's extremely hot. (High air conditioning use, not in terms of it being on, but in terms of high temperature differentials.)

Tip: In hot weather, open windows to get the hot air out, then set on manual, recirculate, 78 degrees (if the outside temperature is 80+), with the vents pointing at you at first, then near you afterwards, running the fan at whatever speed seems reasonable. I thought the recommendation to set the A/C to 78 degrees was for mileage-masochists until I tried it.

3b. You like to drive at interstate speeds with your windows down.

3c. You go uphill to work, then uphill again to home.

4a. You're so enamored with the fact that you can run on battery-only that you do this as much as you possibly can, mistakenly believing that's why the Prius is efficient.

4b. You're trying "too hard" to get good mileage, or based on a naive understanding of how the car actually works: running on battery too much, as in 4a. Or accelerating extremely slowly. Or figuring that regenerative braking is really efficient so braking must be a really good way to charge the battery. Etc. (Read the forums for tips on driving truly efficiently.)

5. You're on your first or second tank of gas. Especially if you measure your MPG by how much gas you put in versus how far you drove, which can be very misleading over short timeframes -- doubly so if you're assuming the dealer filled the tank as you might.

The car's mileage also increases 10% or so over the first 1,000 miles, as the drive train and tires break in.

6. You're not sure what the tire inflation is. Most people who get good mileage do so with tires inflated over Toyota's recommendations (though not more than the tire's sidewall), but you don't need this to achieve 50 MPG. On the other hand, if you're assuming that the dealer set it properly and haven't bothered to check it yourself, that could be the issue.

[ggood]

Originally Posted by afstudio

I purchased my 2010 Prius about 2 months ago and I'm averaging only about 40mpg. I drive 5 miles to work (mostly uphill) but I've put 800 miles on the car and the mile is the same. Do I need to get it checked out?

Andrew, San Rafael CA

Other people, including me, have reported similar mileage with 17 inch wheels, when most of their driving is short trip stop and go. The smart guys tell us there is greater inertia and larger contact patch with the 17 inch wheels, decreasing mileage by 2 to 4 mpgs. I'm assuming the more you have to start from a standing stop, the worse your mileage is gonna be, especially with our larger wheels. Also, there is a 2 to 4 minute warm up period, so short trips kill the mileage.

[gohybrid]

I think i'm finally starting to get a hang of the P&G technique. I think my technique needs a little polishing as far as the ideal duration of the "pulse" and what the threshold for terminating the "glide" should be depending on the terrain... but I managed to pick up almost an extra 4 mpg over my typical average! When I pulled into the garage this afternoon, my average was 59.1mpg over ~60-70 miles.

My commute is about 50 miles round trip, mixed city and highway.

[F8L]

Originally Posted by ggood

Other people, including me, have reported similar mileage with 17 inch wheels, when most of their driving is short trip stop and go. The smart guys tell us there is greater inertia and larger contact patch with the 17 inch wheels, decreasing mileage by 2 to 4 mpgs. I'm assuming the more you have to start from a standing stop, the worse your mileage is gonna be, especially with our larger wheels. Also, there is a 2 to 4 minute warm up period, so short trips kill the mileage.

That is it in a nutshell. Because I regularly swap from stock 15" wheels (185/65/15) to 17" wheels (215/45/17) I see a 4-6mpg drop every time. It's just the nature of the mod.

[windstrings]

Originally Posted by F8L

That is it in a nutshell. Because I regularly swap from stock 15" wheels (185/65/15) to 17" wheels (215/45/17) I see a 4-6mpg drop every time. It's just the nature of the mod.

As good as regen is.. it just goes to show you how much more it could be improved because theoretically if it takes allot of energy to get bigger wheels moving, it should be given back when you brake or coast for regen.... but unfortunately, there are lots of losses.

You would also think that once you get the mass moving, it should be altogether more harder to stop and so coast farthur, but again.... not.

I think the wider tires have more friction, as well has the fact they have to cut a wider path through the wind.

On a vehicle that has almost no friction on the wheels "like a train on steel tracks with steel wheels" this law of physics doesn't seem to affect so much.

[SageBrush]

My wife tends to get 45 - 50 mpg,
I average around 65, and expect 70+ mpg in nice (70ish F) weather

Two main differences I can easily identify:

• She anticipates poorly (much more brake use)
• She does not P&G

I think the excessive brake use is the biggest difference. Most of the car's miles are in suburban/smallish-city driving where aggressive driving is not demanded by other drivers.

[F8L]

Originally Posted by windstrings

As good as regen is.. it just goes to show you how much more it could be improved because theoretically if it takes allot of energy to get bigger wheels moving, it should be given back when you brake or coast for regen.... but unfortunately, there are lots of losses.

You would also think that once you get the mass moving, it should be altogether more harder to stop and so coast farthur, but again.... not.

I think the wider tires have more friction, as well has the fact they have to cut a wider path through the wind.

On a vehicle that has almost no friction on the wheels "like a train on steel tracks with steel wheels" this law of physics doesn't seem to affect so much.

I agree completely with you Alan. I would expect to be able to coast farther with my 17's due to being 6-7lbs heavier than stock but my stockers with Nokians coast alot easier.