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Old 06-26-2012, 10:24 PM   #1 (permalink)
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What's your time worth? Fuel economy vs speed.

I thought I would post this here since it doesn't really fit elsewhere but I like punching numbers and think this might be interesting to some of you here.

I got a scangage on Friday and after some initial tinkering decided to see what kind of difference cruising speed really has on fuel economy.

Before the gage I would mostly cruise at 105km/h feeling it was a good compromise between getting where I am going in good time and saving fuel.

I reset the trip meter approximately every 100km on the open highway alternating between 100, 105 and 110km/h

for the 100km/h runs I got 10.1, 11.7, 11.2 and 10.4l/100km - average 10.9 l/100km
for the 105km/h runs I got 12.7, 11.3, 11.8 and 12.3 l/100km - average 12.0 l/100km
for the 110km/h runs I got 13.2, 11.9, 12.5, and 11.6 l/100km - average 12.3 l/100km

Using $20/hr and $1.25/l the net cost of going 105km/h over 100km/h for 100km was 52˘
Using the same numbers I was surprised to find that going 110km/h over 100km was basically a wash at -.5˘

I always figured going faster would have diminishing returns with fuel burnt trumping time saved. This is definitely not definitive in any way but interesting none the less. I am going to have to mix in a few hundred klicks of going 115 next time I go home and see how that works out.

The data was gathered on a trip from work to home for the weekend then up to La Ronge and back to work today. It is not a good controlled experiment but "psudo-random" I didn't use anything from the first 30km of driving or when I got close to a city where there was other traffic. Datums were from 90km to 125km long but mostly right around 100km. Roads were varied but I was surprised by the variance in readings despite the fairly long intervals. (I thought things would average out since there hasn’t been much wind and little elevation change.)

Anyway thought it was interesting. has anyone else here thought about having a "slow speed" and a "fast speed"? looks like my 105km/h compromise isn't really such a good idea after all.

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Old 06-26-2012, 10:52 PM   #2 (permalink)
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Being retired I have plenty time. If you have the opportunity to turn your time saved into income then time becomes a factor. Most people employed earn a wage for the hours worked. After all of the payroll deductions and expenses you get a fraction of your gross wages. After that what comes out of your pocket is gone forever unless it is paying for an asset. Understanding this means you are paying much more for gas than what you spend, because you have to earn significantly more to have the amount you pay for gas left over after deductions.

I like to keep as much of my money as possible. Getting 45-75 MPG out of my vehicles means money in my pocket.

At $3.50 a gallon 100k miles in a 10 MPG FSP is $35,000.
At 50 MPG it's $7000.

That's $28,000 in my pocket in 100k miles.

Put that in the bank for 5 decades or another better investment. Lets say I bought gold with the gas money I saved for 5 decades at 15k miles a year. Now you are talking about some serious wealth.

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Old 06-26-2012, 11:05 PM   #3 (permalink)
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Thanks for taking the time to do that.

My daily commute includes 20km of 110kph motorway.
Driving that leg at 100, or even 90kph only adds a few minutes to my travel time and aids my fuel consumption.

If I'm on an extended motorway trip (hundreds of kilometres), that extra time can become a problem (worse if I've got passengers) and I usually drive closer to 110kph (averaged between uphill and down).
The increased fuel economy from no stop/start driving more than compensates for the lower fuel economy of the higher speed.

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Old 06-26-2012, 11:21 PM   #4 (permalink)
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I can putt along and my time has not value, when others are in the car the fuel saved isn't worth it. PSL + a few atleast until they fall asleep.
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Old 06-27-2012, 03:01 AM   #5 (permalink)
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I fail to see how driving faster is saving the average person money. When I am driving I am not working therefore I am not making any money. I am, however, spending money on fuel. If i show up to work early i do not get paid more since i am paid a salary. If I choose to drive 60mph I can get approx. 61mpg. If I drive 75mph I may only get 50mpg and I only save 10minutes over my 49mile one way commute. I never understood the whole "my time is worth $$" when you are not actually acrueing hours in your profession. If your earnings are limited by the hours in a day then speeding may make sense but not many professions have this problem.
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Old 06-27-2012, 07:58 AM   #6 (permalink)
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Depends on the trip.

I recently drove back from San Diego to D.C. I averaged approx 70 mph, maybe a bit higher. The added time by reducing speed to 50mph (15 hours) would've cost me an extra day minimum, meaning another hotel stay ($50), 6 more meals ($30), and another day of pay ($160 @ the $20/hr listed above for 8 hours) = approx $240. I make more than $20 an hour, so my cost would've been much higher.

Gas for the trip was only $340... to save $240, we would've needed to get 104mpg @ 50mph. To save enough to offset the cost for me, the car would've needed to get ~2600mpg - enough to make the gas essentially free.

If I could have averaged 80 or 90 without any safety risks or risk of a ticket, I would have.

On a daily basis, the same does not apply (I am salary). I'm not patient enough to do serious hypermiling (and I believe many practices are inconsiderate to other drivers), but I do coast when no-one is around and generally drive with moderate attention to fuel efficiency. But, my time still has some value, so I drive accordingly. I don't race everywhere, but I'm not going to drive 50mph on the interstate either.

Its the same reason some people pay others to work on their car, mow their lawn, repair their house, etc. You only have so much personal time, and sometimes you want to spend it doing something other than driving A to B.

Last edited by ProDarwin; 06-27-2012 at 08:08 AM..
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Old 06-27-2012, 09:08 AM   #7 (permalink)
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What is Time?
What is Value?
What is Money?
What is...?

What do most of us do with the time we have "saved" by getting to our destination faster/sooner? I suspect that the time is wasted in some other manner...

We can not control time, we can control fuel consumption.
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Old 06-27-2012, 10:01 AM   #8 (permalink)
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Probably that saved time will be spent in ecomodder forum :P
Or if you are not hypermiler, then it will be spent by drinking beer and watching something pointless on TV.
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Old 06-27-2012, 10:37 AM   #9 (permalink)
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Originally Posted by meelis11 View Post
Probably that saved time will be spent in ecomodder forum :P
Or if you are not hypermiler, then it will be spent by drinking beer and watching something pointless on TV.
Yes, but who is to argue this is wasted time? I enjoy surfing ecomodder, watching Breaking Bad, cooking my dinner, working on my cars, weightlifting, mountain biking, etc. much more than I enjoy my commute. Leisure time != wasted time.
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Old 06-27-2012, 10:42 AM   #10 (permalink)
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Anyone who is concerned about time=money enough to speed better have a really, really short commute or they are barking up the wrong tree!


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