Tuesday, June 24, 2008

55 Saves Gas???

I've always heard that driving 55 instead of 60 or 65 saves gas. I'd never really paid attention to just how much gas was claimed would be saved. With prices what they are now, and having to go to the Bay Area on occasion, I thought I really should try it out and see if driving 55 does save gas.

Besides, I'm not often comfortable driving 65, especially on curvy roads where I know I couldn't stop in time if something's stopped in the road just around the corner.

I drove down to the Bay Area Sunday and actually checked out the 55 savings. There were a couple problems I started with:

First; I didn't top off the tank before leaving. I usually don't and usually leave Eureka just a gallon or two short of 3/4 of a tank. This time I probably had a gallon or two more than usual to start.

Second; I didn't really decide to take a serious look at the gas mileage until I was a couple miles out of Eureka so I couldn't remember exactly what the gas gauge was reading when I started. Still, I thought I had a close enough idea of where the needle was when we started off that I should be able to detect a difference in mileage.

I started off setting the cruise control to around 56 or 57 miles an hour. Right off the bat I noticed I seemed to be able to run uninterrupted on cruise control for longer stretches of road than I could going 65, or even 60.

By the time we got to around Garberville, I really felt the gas gauge was higher than it normally would have been but, since I didn't remember exactly where the gauge started out at, or where it normally would be at that point. I couldn't say for sure.

Oddly enough, it seemed like we made Garberville in roughly the same amount of time going 56 or 57 as we did going the normal speed. Around an hour and fifteen minutes. Pretty close, anyway.

Stopping at the Willits Safeway for gas, as we usually do, the gas gauge showed what I figured was about 7 gallons used. Figuring we started with the needle just over the 3/4 mark, and made Willits with it maybe a gallon under the half tank mark, I guessed it at about 7 gallons. Normally I figured it took about 10 gallons. I could never say for sure because I never top off the tank before leaving Eureka.

This wasn't accurate enough, though, since I'm basing this on memory of what I wasn't even sure was right, but we can start over again here.

I reset the odometer to zero and filled up the tank. Since we're staying at the same place this time as last trip, the mileage should be pretty much the same. The only difference will be the speed we'll be traveling at.

Driving to San Francisco and back, it seemed to me the needle was considerably higher than it would have been driving 65 but, again, I couldn't be sure. I never paid enough attention to what the gas gauge indicated at any of the points along the road, except for Willits. In Willits, coming from either direction, the needle shows around a couple gallons less than a quarter tank.

Heading back north to Willits on Monday, I was thinking we probably had a quarter tank more than we would normally have and we must be saving quite a bit of gas. I was thinking maybe we'd save five gallons out of a slightly over 20 gallon tank if this held out.

Heading up Ridgewood Grade north of Ukiah seemed to use up gas quicker. By the time we arrived at the Willits Safeway the needle looked to be maybe a gallon under half a tank. Normally at that point it would be a couple gallons below a quarter tank. I was thinking we could have saved maybe five or six gallons.

I wrote the odometer reading of 266.9 miles, on the receipt. The tank took 13.6 gallons to fill-up. I could crunch the numbers on a calculator later to get miles per gallon. I also realized I still had the receipts from our last trip at home and could just compare the two fuel purchase amounts and that would probably show a substantial difference. Anyway, at this point I was convinced I'd gotten a lot better mileage just from where the fuel gauge was when we made Willits.

I make it home and almost immediately crunched some numbers.

I'd checked the freeway mileage for my truck twice a couple years ago. Both times it came to 16 miles per gallon (11mpg in town). This time it came to 19.6mpg, 20 if you round it off. That's quite a bit better.

Then I checked last trip's gas purchases coming from San Francisco to Willits and compared the numbers: Two months ago, making the same trip but going 60 to 65, I filled up with 14.07 gallons. This time I filled up with 13.6 gallons.

WHAT??? That's only a one gallon difference over 266 miles. Something must not be right.

Looking at receipts from driving Eureka to Willits shows the same thing: I bought 14.43 gallons in April and 13.27 gallons this time, yet I was under the impression I started off this time with a gallon or two more than last time.

I must be missing something. Even though I couldn't be sure of the exact gas gauge readings I would normally have, I felt I'd saved more than just one gallon going each way. Seems to me that my gauge usually shows a gallon or two below the one quarter mark when I reach Willits coming from either direction. This time it showed maybe five gallons more than that.

I know I got better mileage. Crunching the numbers shows almost 20mph compared to the usual 16 going 55-57mph, but something's screwy with comparing receipts. I must be missing something. I just know I saved more than a gallon going each way. Then again, numbers don't lie?

And if you're curious about how much longer it took to get back to Eureka going 55-57, we left UCSF Medical Center at around 3:15pm and arrived at Henderson Rite- Aid in Eureka at about 9:50pm. That's roughly the same time it takes us going 60-65. Go figure.

Anybody up to a return to the 55mph on freeways again? It wouldn't bother me.


16 Comments:

At 8:38 AM, Blogger Anon.R.mous said...

Depends on the car or pick-up Fred.

 
At 9:40 AM, Blogger Fred said...

I realize that. What confuses me is on my truck my observations from watching the fuel gauge gave the impression of much better fuel savings than comparing the amounts between receipts. I'm thinking I'm missing something or figuring this wrong.

Even if I actually had started with more gas in April than I remember, that shouldn't matter. All things being equal, except speed, the trip to Willits down and back to Willits shows I only saved one gallon this time when my gas gauge indicated otherwise. It doesn't seem right.

 
At 10:36 AM, Blogger Anon.R.mous said...

You drive a Ford Ranger pick-up right? Those things are little bastards sometimes and won't read right.

 
At 12:50 PM, Blogger Fred said...

'97 Ford F-150, actually, and I think I'm figuring this out finally. Just got to use the calculator to get it right.

 
At 8:05 AM, Blogger Fred said...

Ok. I think my mileage might of improved by 20 to 25% by going 55mph.

Assuming my truck was getting 16mpg on the freeway back when I tested it a few years ago, getting 19.6mpg this last time would be either a 20 or 25 percent increase in mileage- rounding 19.6 to 20, 16+4=20, 4 being 25% of 16.

There should have been about a 3.5 gallon difference between this last fill-up and the same fill- up two months ago, 3.5 gallons being 25% of the 14.07 gallons I filled up with two months ago.

Why does the receipt from the other day show only a one gallon difference? Either their pumps are inaccurate or, more likely, I'm wrongly assuming I drove 60 to 65 doing the same drive a couple months ago. I might well have driven slower than 60-65 simply due to the traffic conditions over much of 101, just as happened this last time. Since I drove slower, I wasn't making the comparison I thought I was making so there wouldn't have been as big a difference in mileage.

A better route to check mileage on would be Eureka to Willits as the traffic there is much less congested for the most part and you can keep a more consistent speed.

Maybe I'll top off before leaving Eureka and check it next time I head south.

 
At 8:34 AM, Anonymous Andrew Bird said...

For a time part of the work I was doing involved taking long road trips from Humboldt to Sonoma & Marin counties and back two or three days per week. I noticed that my Ford Explorer, 4.0 liter V-6, got markedly better gas mileage if I kept it more or less under 60 mph. I never tried dropping it to 55 mph.

 
At 9:37 AM, Blogger Fred said...

Most of the time on the way down I was going more around 56 or 57. From Willits to Eureka I tried to stay at 55/56.

It would be interesting, but expensive and time consuming, to check mileage at a number of different speeds: 70,65,60. 55 and 50. Heck, somebody probably already has and the info is probably online somewhere.

 
At 9:40 AM, Blogger Fred said...

Oh, I might add I found it real difficult to keep my speed steady using the gas pedal. Cruise control seemed the only way to maintain a consistent speed.

Luckily, as I mentioned earlier, I found it much easier to use cruise control for extended periods at the lower speeds. When I'm going faster I always need to speed up or slow down to react to other cars or conditions so sometimes I wonder if it's even worth it to try cruise control at 65 or 70.

 
At 5:19 PM, Anonymous leadfoot said...

Fred, I drive like a bat out of hell, pass everyone on the hills. The car has the worlds most powerful stock engine for its weight class (GTO 400hp 400fp torque) I get 21 mpg. While at 55 I get 24 mpg. Buy a new car and live a little. With the price of todays gas, if you drive at all the savings will make the payments for you.

 
At 9:49 AM, Blogger Anon.R.mous said...

Hey Fred, check your tire pressure and swap out the plugs. It also depends on your gearing. I drove a car that got 28mpg @ 55mph and 33mpg @ 65mph.

Being that I have no clue what your 1997 F150 is running all over, it's hard to say what could be wrong with it. Now the 1997 F250 Diesel I drove once, being a supercab and 4x4 but also being a automatic, got better mileage than that.

 
At 11:57 AM, Blogger Fred said...

Actually, tire pressure was checked when I stopped by the Oil Stop place in Eureka the day before. I also was using two brand new tires.

Another thing I do is drop my tailgate to reduce wind resistance. I don't know how much that helps. I don't see many other people doing it, but I know I could feel the difference the one time I raised my tailgate in Novato and went the rest of the way to SF that way.

 
At 2:47 PM, Blogger Anon.R.mous said...

Fred, why would you believe that tailgate down myth? I mean, that's up there with run your car on water, and there is a carb out there that gives the model T a 100mpg and 200 hp.

 
At 2:58 PM, Blogger Fred said...

I think this one might well be true. For a while we'd make one last stop at Novato where I'd raise the tailgate, before heading into The City. I could feel the difference in the wind resistance. How much gas it saves, I don't know, but I could feel the difference.

You may not notice it if you hadn't had the tail gate down, but if you drive for a while with the gate down and then close it, see if you can tell the difference.

 
At 3:46 AM, Anonymous Anonymous said...

October '97 Car Talk article on how tailgate position affects gas mileage (and safety). Engineers say up is better.

 
At 5:28 AM, Blogger Fred said...

Wow. It sure feels like it reduces wind with it down. Thanks. I guess I'll just leave the gate up from now on.

 
At 5:53 PM, Blogger Tom Sebourn said...

I have been driving at 60 instead of my usual 65 to 70 mph. I have a 5 speed 1600cc. Kia. I was getting about 27 to 29 mpg. At 60mph I am getting about 30 to 32 mpg. Was getting 34 mpg until I got new tires with tread on them.
It takes a bit getting used to but if I am getting 30 more miles per tank full, that's a free trip to work.

 

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