Sun
May 20 2007
06:26 pm
By: R. Neal  shortURL

The MPG/trip meter was reset to zero in the driveway on our way out, and here it is in the garage after an afternoon drive up to Townsend and around the Cades Cove loop with a short side trip up Parson's Branch Road.

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River Dog's picture

Wow how did you do it ??

What sort of tires and what pressure do you run them at? Is nitrogen an option in your tires? Good for you I wish there were more hybrid owners and initiatives, tax credits etc.

R. Neal's picture

They're the stock tires that

They're the stock tires that came on it, "Goodyear Integrity", with whatever air pressure they came with from the dealer (which I should probably check).

There was some discussion earlier about Toyota's switch to these tires and the fact that they are not technically "low rolling resistance" tires.

As for how I did it, mainly, I drove. Mrs. Leadfoot consistently gets 10% or so fewer MPGs than me. Today we didn't run the AC because it was pleasant outside and we just rolled down the windows if it got hot. That probably helped.

Plus I was trying to get maximum MPG, so I was careful to anticipate red lights and stops, not accelerate hard, generally drove the speed limit, and overall just kept a light touch on the gas pedal except as needed and used cruise control where it was practical. Sometimes it seems like it's better to accelerate a little harder to get up to speed and then let it glide into electric or electric/assist mode.

Probably got some bonus from the fact that we went about 75% of the way around Cades Cove loop on battery power, and charged the battery real good coming down off the mountain which let it run more in battery assist mode on the way home.

michael kaplan's picture

running the a/c

"Today we didn't run the AC because it was pleasant outside and we just rolled down the windows if it got hot."

In a short drive around town today I noticed that about 80% of vehicles had their windows tightly sealed and air conditioners running. That in spite of cool and pleasant weather. Am I missing something, or are people totally out of touch with reality?

00Stephen's picture

Am I missing something, or

Am I missing something, or are people totally out of touch with reality?

Probably a bit of both. Conventional (ie circa ~1980) wisdom suggests that running the air conditioner has a noticable and negative on gas mileage. Conventional wisdom also suggests the increased drag co-efficient caused by driving with the windows down has a noticable and negative effect on mpg. But in reality, while these factors negatively affect fuel economy, the difference is almost negligible.

(link...)

Unloading junk from the trunk, maintaining factory recommended (or higher) tire pressures, and being easy on the throttle are all going to affect fuel economy more than than what accessories you're running in a modern cars, or whether your windows or up or down.

As for why they chose to be cooped up, maybe they didn't want to mess up their hair? After all, less Aqua-Net sprayed means less CFC's unleashed upon the ozone layer, right? Oh wait, that was another ~1980 issue.... n/m.

temp's picture

Integrity Tires

Regarding your tires, I'd be interested if you have the same experience that I did. I liked the Goodyear Integrity tires. They lasted about 40-45k miles and when I replaced them with Goodyear Triple Treads my mileage sank about 5 mpg. Ticked me off until I realized it was because the diameter of the old tires had gradually decreased with tread wear and made my mpg's look better than they actually were (more revolutions of the wheel per mile traveled).

River Dog's picture

Braking with the stick shift

Do you use the brake feature on the stick to charge? I was told to use this on downhill and to decelerate from fast speeds.This is supposed to charge batteries faster.

Have you seen the electric conversion kits

(link...)

R. Neal's picture

Do you use the brake feature

Do you use the brake feature on the stick to charge?

Yes, in fact I did for a bit coming down off the mountain, mainly to help keep off the brakes. It did seem to make it charge a little harder. The battery charge indicator was full green when we got to the bottom. I'm going to start paying more attention to using that when appropriate.

And yes, I've heard of that conversion kit and some other plug-in mods (plus another one that will let you use your Prius as a backup power generator for your house in case of power outages). Since our Prius only has about 1800 miles on it I'm not quite ready to start hacking it.

But it's puzzling why they don't offer the plug-in option or the "electric mode" button in the U.S. There have been lots of times when I wondered why it wasn't running electric only, and wished I had an option to force it. I blame Dick Cheney.

But seriously, the Mrs. and I were talking about it, and I think the next generation hybrids should focus on battery technology first, and then a plug-in option to help keep it topped off when not in use. It's weird how ours starts the gas engine a few seconds after backing out of the garage. I'm assuming it's to charge the battery.

River Dog's picture

Keep the pressure on for tax incentives and development

Enhanced electric hybrids and TVA allowing you sell the electricty generated by PV panels on your home at a higher price than you purchase it are a good combination.

Charge your car at night when rates are cheapest and demand is low - and sell back to the grid in the daytime when rates and demand are higher.

Problem is the U.S. gives very little breaks to those willing to purchase the P.V. techonolgy.If they allowed a total tax deduction it would revolutionize the how we do business, improve air quality, and free our dependence on oil.

Wind power and green energy will be the only thing we really can be doing to save ourselves. I'm hoping we pressure the new administration for radical change in this area.

By the way I like your blog and the layout!

temp's picture

-

It's weird how ours starts the gas engine a few seconds after backing out of the garage. I'm assuming it's to charge the battery.

The Prius' gas engine runs to warm up regardless of the battery level. It needs to stay warm in order to reduce emissions. This is why it carries an electrically heated water tank that circulates hot water through the engine block while you're running on battery power. The pump on this tank is the whining sound you hear after parking your car. Depending on outside temperature, the tank can sometimes supply enough heat to keep the engine warm for quite awhile while you're driving on the battery.

The other big need for heat is us humans during the winter months. These two factors reduce my winter mileage by about 10 mpg.

The gas engine usually doesn't run while the car is in reverse, so it waits for you to put it in Drive, then starts the warm-up.

R. Neal's picture

The Prius' gas engine runs

The Prius' gas engine runs to warm up regardless of the battery level.

Interesting. I had read something about a pump and a "thermos" to store hot water. Thanks for the explanation.

This also explains why we seem to be getting better mileage as the weather warms up. (That and maybe engine break-in?)

temp's picture

Interesting

Interesting. I had read something about a pump and a "thermos" to store hot water.

Yeah, it is kind of interesting. I was surprised at how much gasoline I burn just to keep the air warm inside. Some of the mileage fanatics block airflow into their engine compartment in the winter. Toyota needs to put a blanket on the engine, even for summer driving ... just the opposite of what we usually think about with our automobiles.

Factchecker's picture

Charge your car at night

Charge your car at night when rates are cheapest and demand is low -

I didn't think TVA rates vary around the clock. I'm almost sure they don't--am I missing something? Some places like Cal. and maybe eventually here, though.

Am I missing something, or are people totally out of touch with reality?

They sure are. Especially us "fiercely independent" Tennesseans! Why have 76 degrees when you can have 70 degrees and shut out the horrible outdoors too? Course if it's winter, you'd set your heater for 76 degrees.

Very cool on the 65.9MPG! I try and make it a habit to always drive in the manner described--easy on accelerating, letting up long before stops, etc. Makes a big difference. Better for the car too.

I bought me some new tars yesterday and Fisher filled 'em w/ N2. I didn't look at the receipt, but I hope they didn't charge extra. I have a hard time believing they really think it has any effect other than as hype to sell.

Carole Borges's picture

That's amazing!

Your posts about the new car are sure to inspire everyone. I'm learning a lot.

mjw's picture

To AC or not to AC

Am I missing something, or are people totally out of touch with reality?

Or maybe they are doing what I do, which is to rely on the excellent air circulation provided by the fans in my Honda to bring the outside air in without losing MPG by running the AC or by having the windows open.

DaveG's picture

Was "charge indicator" at same level pre- and post- trip?

Seems as though your car would give an articially high MPG number for a trip if the battery were fully charged at the beginning of the trip and near depletion at the end.

Especially on a trip where you spend 70, 80 or 90 percent of the travel time on battery power.

Factchecker's picture

A/C, good or bad for MPG?

But in reality, while these factors negatively affect fuel economy, the difference is almost negligible.

This is one of those hard to prove either way things, but I would argue that A/C is usually more detrimental to mileage. Most articles that tout aerodynamics as more than compensating for the drag on the engine are industry pieces. The auto industry wants you to be happy and comfortable. I think it depends mostly on the aerodynamics of the particular car, windows up and windows down, and of course speed, which causes drag to increase exponentially.

Certainly in low speed stop/go city driving, the A/C would only be another load for the engine. The aero effects would be very small compared to the BTUs needed to dehumidify and cool.

As for cruising, drag varies considerably by car model. Consider how different wind noise can be in different cars, say, when you're driving with just rear windows open. Some are very noisy, others not so much.

The simple test in the link is pretty much just anecdotal for one set of conditions.

FWIW, no matter how hot it gets I usually remember how things were before A/C and just tough it out, except on the interstate for more than a few miles.

redmondkr's picture

Practically everybody I know

Practically everybody I know is doing something to conserve. Two of my neighbors and I frequently carpool on grocery runs. Meanwhile, take a look at this item in the San Francisco Chronicle.


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Knox A-Hole's picture

Our good friends at TVA

... and TVA allowing you sell the electricty generated by PV panels on your home at a higher price than you purchase it are a good combination...

Are you kidding? Those bastards at TVA aren't "allowing" anything. It's a federal law on co-generation that they would rather be exempt from.

I didn't think TVA rates vary around the clock.

They do, but I doubt very seriously that the bill you get in your mailbox every month is from TVA. KUB and other electric distributors in this area typically do not meter this way. It requires the customer to install a special (read: expensive) meter, and is generally reserved for industrial customers.

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Rachel's picture

Ha! I spit on your 65.9

Ha! I spit on your 65.9 mpg! As we speak, my Civic sits in the carport with the indicator reading 103 mpg for this tank.

"This tank," of course, being what we used on the 2 mile drive home last night from the Sevier Avenue gas-station-formerly-known-as-Pilot.

:)

bizgrrl's picture

For the first 10 years of

For the first 10 years of our married bliss we did not have A/C in a car and barely had any A/C in the house. One summer evening it was so hot we went outside to throw the frisbee to cool off. Years ago my Dad and Mom drove us to Houston TX in the middle of the summer with no A/C in the car. We hung our heads out the windows like dogs. My parent's house (about 2,800 sq ft) still has a single window A/C unit to cool only a few rooms. They have lots of trees that keep the house pretty cool. Their neighborhood is usually 5-8 degrees cooler than other areas in town.

Sure I appreciate A/C. It really helps to prevent mold. I really like fresh air. I frequently have my windows open in the car, "increased drag co-efficient" be damned. We're adding more screen doors to the house this year.

"Consider how different wind noise can be in different cars, say, when you're driving with just rear windows open. Some are very noisy, others not so much." Our Freestyle rear windows can be quite noisy when opened to a specific point. They made such a weird, loud noise on the interstate one time I stopped to see if there was a problem with the car, tires, etc.

Factchecker's picture

Seems like most cars can't

Seems like most cars can't be driven with only back windows open, there's so much buffeting. But there apparently is a lot of variation in noise for other windows and the sunroof, which I'm sure affects the drag, sometimes considerably. I remember Click and Clack discussing this a few months ago where I believe they were lamenting that many cars just aren't friendly to riding with the windows opened.

Maybe if newer generation cars are generally worse w/ windows open and better w/ them closed, then that supports the argument that A/C is better for mileage while cruising. But most people seem to just keep the A/C on from April to October wherever they go.

I remember the long vacation we took out west in our '63 Buick Special wagon. They said it was over 100 degrees when we stopped in Little Rock. My dad got a window-hanging "swamp cooler" from Sears for the trip. We kept telling mom to pull the string to chill the measly air flow out of the thing. Never seemed to help at all.

Up Goose Creek's picture

Car AC

I've noticed that it helps considerably to roll the rear window down a bit when the front window is open.

I didn't own my first air conditioned car until I was 34, now there's no going back*. I belive my mom didn't own her first air conditioned vehicle until she was 71. It seems she finally figured out that Xtreme frugality has its limits.

* well the AC on Ye Olde Vanne is long since gone, but I've found this has the side effect of encouraging me to get out and get hauling errands done early in the morning.

___________________________________
Less is the new More - Karrie Jacobs

Cletus's picture

Some folks, like my

Some folks, like my significant other, uses the a/c in the car because of bad allergies. The s.o.'s eyes and nose will get all runny and irritated driving with the windows down.

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