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Discussion Starter #1
...and it is absolutely true that speed makes a HUGE difference in the overall MPGS's.

I drove from LA to San Fran this past weekend (a 400 mile drive) and on the way up drove as I normally would, not using cruise control very often and averaging probably a little over 70 mph.

On the way back, I set the cruise control at 65 the entire way, only touching the gas pedal to pass the occasional semi.

Now, the drive north to San Fran is decidedly more uphill than the drive back to LA is, but the overall MPG difference was staggering.

LA to San Fran: approx. 44 mpg
San Fran to LA: approx. 51 mpg

That's huge!! And both trips took virtually the same amount of time, 6 and 1/2 hours.
 

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Trips

I saw 46 mpg from Alabama to Tennessee, the rest of the trip to Pennsylvania averaged 51 mpg. Getting over the Smokies uses a lot of gas. I drove from Mobile, AL to Savannah, GA was getting 46 mpg, filled up at the GA-AL border, and had 54 mpg from there to Savannah. Your observations are right, elevation change makes a big difference in mileage. (2005 Prius - 23,000 miles)
 

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evaunit6 said:
...and it is absolutely true that speed makes a HUGE difference in the overall MPGS's.

Now, the drive north to San Fran is decidedly more uphill than the drive back to LA is, but the overall MPG difference was staggering.

LA to San Fran: approx. 44 mpg
San Fran to LA: approx. 51 mpg

That's huge!! And both trips took virtually the same amount of time, 6 and 1/2 hours.
Aren't both SF and LA basically at sea level? If so, assuming you drove the same route and distance each way, a roundtrip from one to the other would entail the same amount of ascent and descent. IMO, your difference in mpg going and coming had nothing to do with elevation differences and everything to do with your driving techniques.
 

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Although LA and SF are both at sea level, the up hill segments coming north are much more gradual, eating up fuel at a greater rate. Going south, one goes up the Altamont Pass and the Grapevine very quickly, coming down very gradually. At the same speed, mileage can be about 10% greater going south. I recently completed an SF-Vancouver round trip in my '05, keeping 60-65 mpg on cruise control and averaged 52 mpg for the whole trip. Similarly, I got about 45 mpg on an SF-San Diego round trip, but on interstate much of the time, going with traffic, about 70 mph.
 

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GAZ MZR said:
Although LA and SF are both at sea level, the up hill segments coming north are much more gradual, eating up fuel at a greater rate. Going south, one goes up the Altamont Pass and the Grapevine very quickly, coming down very gradually. At the same speed, mileage can be about 10% greater going south. I recently completed an SF-Vancouver round trip in my '05, keeping 60-65 mpg on cruise control and averaged 52 mpg for the whole trip. Similarly, I got about 45 mpg on an SF-San Diego round trip, but on interstate much of the time, going with traffic, about 70 mph.
Sorry, but with the information you have presented on your SF/Vancouver and SF/San Diego trips you have not convinced me that a ROUND TRIP at the same average speed and over the same distance would result in different average miles per gallon on each leg of the round trip from start point to return point.

Did you keep your gas receipts? If you can provide evidence of the gallons consumed on each leg and the distance travelled on
each leg your emperical conclusions would carry more weight.

I submit that the different fuel economies you experienced on your trips had everything to do with your average speeds and little to do with differing elevations encountered.

Theoretically, a round trip from SF to Denver would yield equal average miles per gallon going and coming. In practice, because of variations in temperature and engine efficiencies under load and no load conditions the results would differ.

Sorry if I appear to be argumentative but what you and the original poster are presenting as facts violate some basic laws of physics.

Anyone else care to chime in with actual data, not emperical conclusions? :D
 

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Wind direction and speed can be a big influence on MPG.
To be truely scientific, you would need 2 cars, one travelling one speed, the other car the other speed, along the same route. Even then, vehicle differences can cause deviations, but I believe at the speed differences, the vehicle differences would be negligable.
 

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Discussion Starter #7
I submit that the different fuel economies you experienced on your trips had everything to do with your average speeds and little to do with differing elevations encountered.
If you'd actually read my original post, you might have surmised that I was relating to everyone that the average speed was the cause of my higher MPG's for the trip. I simply stated that the drive from LA to San Fran is more uphill than down, and if you've actually driven that route at all, you'd know that too.

Why do all the sanctimonious Prius owners always have to poo on everything? Why do I need to convince you of anything? I'm just stating my personal experience based on what my display showed me...that's really all there is to it.
 

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evaunit6 said:
Why do all the sanctimonious Prius owners always have to poo on everything? Why do I need to convince you of anything? I'm just stating my personal experience based on what my display showed me...that's really all there is to it.
Well of COURSE you got better mileage on the way back. If you look on a map, you'd see clearly that San Francisco is UP and LA is DOWN. :p
 

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LA to SF Mileage

I agree with "evaunit6" on the different mpg readings on reverse legs of this trip. On steep grades, the mileage is about the same regardless of the incline, so the duration (length of time) spent at the lower mpg really affects the total trip mileage. Also, the slower descent lengthens the duration at higher mpg readings.

This becomes more obvious on an exaggeration of this trip, here in Arizona. If you drive from Phoenix to Tuba City, over Flagstaff, you get an hour and a half of nearly constant climbing followed by about 30 minutes of rapid descent. On the reverse trip, you get 30 minutes of constant climbing, followed by an hour and a half of slow descent. The mpg readings on these two legs will vary by as much as 10-15 mpg, though I am unsure whether Phoenix and Tuba City are exactly the same elevation.
 

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I submit that the different fuel economies you experienced on your trips had everything to do with your average speeds and little to do with differing elevations encountered.
I simply stated that the drive from LA to San Fran is more uphill than down, and if you've actually driven that route at all, you'd know that too.
You are starting at, and finishing at esentially sea level, so the drive to SF is not more uphill than down (depending on where in each city you start from). Nor is the reverse true For both directions, you go up and down the same amount. And, yes I have driven the route, more than once. And there is nothing "sacntimonious" about it -- it is geography. If you start at 0 ft and end at 0 ft, and take the same route, one route has as much climbing as the other. One direction may be more or less steep than the other, but the elevation changes should be the same. Unless you have a magic Prius?
Now if you go to Tahoe from SF, now you are talking about a route that is more climbing one way than the other.

But as Pheonix says the impact of the rate of climb or decsent may be a factor, I haven't tested that.

Spike
 

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evaunit6 said:
Why do all the sanctimonious Prius owners always have to poo on everything? Why do I need to convince you of anything? I'm just stating my personal experience based on what my display showed me...that's really all there is to it.
FWIW, I thought it was a fun experiment, and was happy to see it posted here. Sure, there's wind and topography, and mood swings, and cosmic dust, and rotation of the Earth. But it was still neat. :) Keep it up, evaunit6.

And Prius owners should know that if they poo while they are here, they should put it in a baggy and take it with them, rather than leave it for someone else to deal with.
 
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Glad to hear you enjoyed your trip. I don't doubt for a minute the mileage you posted. It gets me pissed that someone would even question it.
 

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When in school I frequently drove from San Anselmo (just north of SF) to San Luis Obispo (about 90 miles north of Santa Barbara). I'm one of those anal retentive freaks that keeps track of all mileage on all my cars since I was 16. The MPG on the trip south (in a 1973 Mercury Capri) was always better.

I've since assumed it was due to the wind patterns. When you see the weather reports on the news here in CA the storms generally move from North to South. I never thought about the types of hills there are on that stretch of road, maybe that's the reason. Or maybe they are contributary.

Jeff
 

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This is from a recent Cartalk. The dollar amounts are for a regular car, not a Prius. But not matter what you drive, speed kills mileage.

"Because wind resistance increases dramatically with speed, every mile that you drive at a speed over 55 MPH, your fuel economy actually goes down by two percent. In other words, you'll get about half the mileage driving at 70 MPH compared to 50 MPH! That's why aerodynamics have become so important in the last 15 years, and why all of our cars now look like jelly beans.

Here's another rule of thumb, from the EPA: Every 5 MPH you drive over 60 MPH you're paying an additional $0.21 per gallon for gas. "
 

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We just got home from a 5,018 mile trip( a big loop not round trip) , from New Mexico, Colorado, Wyoming(through Yellowstone), Montana, Idaho, Wash,(coastal 101) from Wa to CA, Az then back to New Mexico. Total MPG average was 50.4 Speed from 30 to 70 MPH sealevel to over 10,000' Temp from 20's to 90's. This was as unscientific as it gets. Good MPG and a real comfortable car for 2 people and luggage.

Stan

05 Salsa red pkg 5 9980 miles on car.
 

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Rotation of the earth. Gee, I hadn't thought of that.

Nobody is questioning the mileage, we are discussing the cause of the shift. Nobody doubts that driving faster will reduce your MPG, but what we are discussing is how much?

I don't get 30MPG when I drive 70, it is more like 45+. Yet I don't get 80 when I drive 50, it is more like 60MPG.

$.20/5MPH increase? That doesn't seem to add up, but it does depend on many variables, 2 being the initial miles/gallon at 50MPH, and the price of gas.
 

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Discussion Starter #18
For those interested, here are the final stats for the tank of gas that got me back from San Fran, as I just refilled again today after the gauge began to blink:


Date tank filled:
10/30/05
Gallons filled: 8.8
Average speed: 65 mph
MPG's: 50.9
Total tank mileage: 450
 

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Evaunit, I have experienced the same type of situation, but it was me going 65-68 and my S/O going 71-74. Glad you discovered that!

Chas- yes, your reply was harsh, I took it that way too. What was your point? Dan, you've been on here long enough to notice how "in your face" his post was.

SPEED is the biggest gas guzzler on hwy driving.
 

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Sorry, I disagree. Chas' posting here was probably the least 'in your face' of his postings. We are just trying to point out the other variables that can shift the results, not just the speed. If you want to generalize and say 'increase speeds reduce milage', few would argue that point. But if you give specifics 'Increasing to 70MPH gives you 30MPG', that can and I certainly will challenge that, as that is NOT my experience. However if you drove 70MPH into a 40MPH headwind with tires inflated to 30#, then you might get 30MPG.
 
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