Highway mileage

[aeronaut]

Just got back from visiting my mom in Iowa.

On the way there, set the cruise control at 74 mph (took the autobahn, so it was legal.) Got 42.0 mpg for the trip there.

On the way back, set the cruise control at 65 mph. Got 48.4 mpg.

Caveats - the way there was during the day, with the AC on, but pretty low. Way back was mixed, in the evening. I had the AC on at first, and then turned it off when I had to put the lights on. Mileage seemed consistent for the two legs, perhaps a hair better with the lights over AC. But the mileage back was no less than 48.2 mpg with the AC on.

Also, now that I'm back, the car's overall mpg seems better, on the street and highway. At the end of the trip, I had 1500 miles on the car, so the trip may have helped break it in. I'll repeat a similar experiment on the next visit, compare and report.

Regards,
aeronaut

[alexstarfire]

Unfortunately going there and back from a place aren't really comparable. One may be slightly uphill while the other one is slightly downhill. Interesting to see that even at 74MPH that you still got 42 MPG, but I don't think those are very comparable.

[subarutoo]

I do 90 miles a day at 70+ mph for most of the trip. Lifetime average is over 50.3 mpgs, in 38,000 miles over the last year and a half +. Its almost impossible to drive the same exact road at a given speed for comparison. I guess you might use the Scan gage to compare average speed over the same trip every day, and get a ball park comparison of speed vs. mpg. One trip won't provide much data. Just drive the car. Don't think too much about it. The Prius will do better than any other car you've probably owned, at least for me.

[ystasino]

<div class='quotetop'>QUOTE(aeronaut @ Jul 26 2007, 10:06 PM) [snapback]485883[/snapback]</div>

Just got back from visiting my mom in Iowa.

On the way there, set the cruise control at 74 mph (took the autobahn, so it was legal.) Got 42.0 mpg for the trip there.

On the way back, set the cruise control at 65 mph. Got 48.4 mpg.

Caveats - the way there was during the day, with the AC on, but pretty low. Way back was mixed, in the evening. I had the AC on at first, and then turned it off when I had to put the lights on. Mileage seemed consistent for the two legs, perhaps a hair better with the lights over AC. But the mileage back was no less than 48.2 mpg with the AC on.

Also, now that I'm back, the car's overall mpg seems better, on the street and highway. At the end of the trip, I had 1500 miles on the car, so the trip may have helped break it in. I'll repeat a similar experiment on the next visit, compare and report.

Regards,
aeronaut
[/b]

The AC will not impact your mpg on the highway significantly since it is operated by the battery which is almost always fed when in CC a high speeds.

What tire pressure are you running?

[SureValla]

lights on? that matters?

[brick]

Running the A/C reduces my highway mileage by a reliable 7-8%. (That's better than my old Accord that was hit by at least 15%...chalk it up to the variable speed compressor working its icy magic.) It may not drain the battery like it does in city conditions (ouch) but it does require a fair amount of energy to move all that heat up-hill.

[Danny Hamilton]

<div class='quotetop'>QUOTE(brick @ Jul 27 2007, 08:33 PM) [snapback]486471[/snapback]</div>

Running the A/C reduces my highway mileage by a reliable 7-8%. (That's better than my old Accord that was hit by at least 15%...chalk it up to the variable speed compressor working its icy magic.) It may not drain the battery like it does in city conditions (ouch) but it does require a fair amount of energy to move all that heat up-hill.
[/b]

That sounds similar to what I've seen. In particular, I've found that setting the auto climate control in the mid 70F range, with the car in full sun at noon when the outside temp is 85F to 95F, the A/C uses around 0.15 to 0.20 gallons per hour. If the car moves 1 mile in that hour, Ouch. Big hit to your MPG. If you are traveling at hwy speeds for that hour an additional 0.15 added on to the 1.5 gal or so that you are burning anyhow is only a hit of 10% or so. Less if the temp outside is cooler, it is overcast at all, or you bump up the interior temp a bit.

[aeronaut]

I started the trip in Evanston, ended in Marion, IA. Evanston is 600 feet above sea level, Marion is 850 feet above. The trip was over 250 miles in length.

What I was looking for was the change in MPG as a function of speed. I'm not willing to get on a test track to cancel out wind, elevation, etc, as that would be wasting gas to do the test. But while I'm travelling, I can do certain "experiments" and get some info about the car.

Both A/C and lights will drain power from the car, which eventually comes from the gas tank, costing one some MPGs. How many is the question, and is a function of the outside temperature for the A/C. Lights will also cost you some, although probably not as much.

Regards,
aeronaut

[morpheusx]

<div class='quotetop'>QUOTE(aeronaut @ Jul 26 2007, 10:06 PM) [snapback]485883[/snapback]</div>

Just got back from visiting my mom in Iowa.

On the way there, set the cruise control at 74 mph (took the autobahn, so it was legal.) Got 42.0 mpg for the trip there.

On the way back, set the cruise control at 65 mph. Got 48.4 mpg.

Caveats - the way there was during the day, with the AC on, but pretty low. Way back was mixed, in the evening. I had the AC on at first, and then turned it off when I had to put the lights on. Mileage seemed consistent for the two legs, perhaps a hair better with the lights over AC. But the mileage back was no less than 48.2 mpg with the AC on.

Also, now that I'm back, the car's overall mpg seems better, on the street and highway. At the end of the trip, I had 1500 miles on the car, so the trip may have helped break it in. I'll repeat a similar experiment on the next visit, compare and report.

Regards,
aeronaut
[/b]

as far as break in, I drive mostly (70 %) in urban highway situations (heavy traffic 55-60 mph) and somewhere around 7500 miles I hit a break in point where no matter what, my mpg will stay above 55 regardless of A/C, and traffic conditions. My original goal before ownership was 50 mpg, then i bumped it to 55 (now approx. my lifetime avg). Now after about 20 tanks, I have frequently flirted with 60 mpg and just barely busted it twice and now my goal is to try to bust 60 more regularly and start flirting with 64 (double my last cars 32mpg) To help today i just boosted my tires from 42f / 40r up to 45f / 43r.

[diamondlarry]

<div class='quotetop'>QUOTE(morpheusx @ Jul 28 2007, 09:39 PM) [snapback]486880[/snapback]</div>

To help today i just boosted my tires from 42f / 40r up to 45f / 43r.
[/b]

OH NO! You went over the tire manufacturer's max sidewall recomendation? I predict doom, destruction, and disruption of the space-time continuum.