# Fuel economy at reduced speed - calculating cost per hour savings **URL:** \ **Category:** Power/Fuel\ **Created:** [May 17, 2022, 2:20pm UTC](https://community.cartalk.com/t/fuel-economy-at-reduced-speed-calculating-cost-per-hour-savings/184195 "2022-05-17T14:20:11Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![circuitsmith](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/circuitsmith/32/40376_2.png) [@circuitsmith](https://community.cartalk.com/u/circuitsmith)\ **Post date:** [May 18, 2022, 5:06pm UTC](https://community.cartalk.com/t/fuel-economy-at-reduced-speed-calculating-cost-per-hour-savings/184195/21 "2022-05-18T17:06:00Z")
> [@Renegade](#): > > As usual the SNOWMAN don’t want to hear any ideas but his own. “Ignore” button FTW. It is however amusing to read the replies. Edit: the above refers to replies to posts I ignore, then guess at what the ignored post said. ---
**Author:** ![Renegade](https://avatars.discourse-cdn.com/v4/letter/r/b4bc9f/32.png) [@Renegade](https://community.cartalk.com/u/Renegade)\ **Post date:** [May 18, 2022, 5:10pm UTC](https://community.cartalk.com/t/fuel-economy-at-reduced-speed-calculating-cost-per-hour-savings/184195/22 "2022-05-18T17:10:53Z")
> [@circuitsmith](#): > > It is however amusing to read the replies. That is why I don’t use the Ignore button for him. 😃 ---
**Author:** ![PvtPublic](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/pvtpublic/32/13089_2.png) [@PvtPublic](https://community.cartalk.com/u/PvtPublic)\ **Post date:** [May 18, 2022, 6:15pm UTC](https://community.cartalk.com/t/fuel-economy-at-reduced-speed-calculating-cost-per-hour-savings/184195/23 "2022-05-18T18:15:11Z")
> [@TheWonderful90s](#): > > **Tell me your fuel economy in MPG or gallons per mile at two speeds, your fuel cost, and I’ll tell you how much you could save** per increased unit of time by driving slower. Tell me what your fuel economy is at 60 MPH on a flat stretch of road, and then reset the computer and tell me what it is at a higher speed like 65 or 70. If you don’t have a flat stretch of road, then drive the exact same distance twice on the exact same section of road at both speeds and record the fuel economy for each trip. > > For most cars slowing down to less than 60 MPH isn’t going to save you money unless you bring home less than something in the ballpark of $12 per hour with gasoline prices at $4 per gallon. This assumes that time spent driving takes time away from work. If you have a fixed salary then you have to decide if you want that extra tax free money that comes from spending more time on the road. Driving slower also significantly increases safety, so the advantage isn’t just extra money. > > Below is an explanation of wind resistance and an example of a car that uses 1/30 of a gallon per mile at 55 MPH with $4 per gallon fuel. The fuel economy at another speed isn’t known so it is estimated. > > _Look at slowing down to save fuel like this. Wind resistance is the cube of the speed, so if you go twice as fast there is 8 times as much wind drag. But you get there twice as fast, so that brings the cube down to a square. Driving twice as fast uses four times as much fuel, and eight times the engine power, if wind resistance alone is considered._ > > _Some of the friction from driving a vehicle, such as drive train efficiency with a locked torque converter or manual transmission, is mostly linear, so speed doesn’t have much effect on efficiency. Gasoline engines tend to be a bit more efficient at higher load (torque at constant RPM), so driving faster increases engine efficiency. Then there is wind resistance loss which increases with the square of the speed. If your torque converter isn’t locked, then the loss from that will increase too as drag increases, increasing the exponential loss even more._ > > _The goal here is to calculate the decrease in travel time due to increased speed compared to the increased cost. For instance, if you’re pulling a big trailer with lots of wind resistance, driving faster than 55 MPH could cost $20 in fuel per hour of saved travel time. Are you missing work due to travel time that pays $50 per hour after all taxes? Then it is worth it for you to drive faster in this situation._ > > _The fuel price in this example is $4 per gallon._ > > _Figuring out how much loss is due to wind drag is the tricky part. Say I get 30 MPG at 55 MPH ($0.1333 per mile) , and I get 60 MPG at 55 MPH ($0.2667 per mile) with a 55 MPH tail wind. In this case half of my energy is used to overcome wind resistance. I’ll ignore the increased engine efficiency at higher load in this example._ > > _60^2 / 55^2 = 1.19 Increasing from 55 to 60 MPH increases my wind loss by 1.19. If that is half of my energy, then it becomes 1.095, so 1.095 (109.5%) as much fuel used to go 60 MPH. $0.1333 per mile at 55 MPH now costs $0.146 per mile at 60 MPH. That’s a $0.012667 per mile cost increase. 55 MPH is 0.0181818 hours per mile, and 60 MPH is 0.0166667 hours per mile. That’s a 0.0015151 hour decrease to go a mile at 60 MPH, and you save $0.012667. **Now do $0.012667 / 0.0015151 hours = $8.36 per hour saved.** So in that example if you’re making minimum wage then going 55 instead 60 is probably worth it for you. Any decrease in speed down to 55 will be worth it for you. As you go past 60 MPH the wind resistance becomes a bigger factor and that $8.36 figure grows. Saving as much as $30 per hour by driving 69.9 MPH instead of 70 MPH while pulling a big box trailer wouldn’t surprise me._ I guess if you can’t dazzle them with your brilliance, then baffle them with your bulls@#t ---
**Author:** ![Renegade](https://avatars.discourse-cdn.com/v4/letter/r/b4bc9f/32.png) [@Renegade](https://community.cartalk.com/u/Renegade)\ **Post date:** [May 18, 2022, 7:00pm UTC](https://community.cartalk.com/t/fuel-economy-at-reduced-speed-calculating-cost-per-hour-savings/184195/24 "2022-05-18T19:00:04Z")
> [@PvtPublic](#): > > I guess if you can’t dazzle them with your brilliance, then baffle them with your bulls@#t Yep that’s the SNOWMAN more BS than Red Green ever had. 🙃 🙃 😆 ---
**Author:** ![circuitsmith](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/circuitsmith/32/40376_2.png) [@circuitsmith](https://community.cartalk.com/u/circuitsmith)\ **Post date:** [May 18, 2022, 8:03pm UTC](https://community.cartalk.com/t/fuel-economy-at-reduced-speed-calculating-cost-per-hour-savings/184195/25 "2022-05-18T20:03:06Z")
> [@Renegade](#): > > That is why I don’t use the Ignore button for him. My time is too dear for that. 😴 ---
**Author:** ![Barkydog](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/barkydog/32/2470_2.png) [@Barkydog](https://community.cartalk.com/u/Barkydog)\ **Post date:** [May 18, 2022, 9:16pm UTC](https://community.cartalk.com/t/fuel-economy-at-reduced-speed-calculating-cost-per-hour-savings/184195/26 "2022-05-18T21:16:45Z")
Speed limit went from 65 to 70 for much of the sometimes 535 mile trip. Speed was 73 or 78. I got 22 miles per gallon both situations based on miles and gas used. Trailblazer 6 banger. ---
**Author:** ![TheWonderful90s](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thewonderful90s/32/29584_2.png) [@TheWonderful90s](https://community.cartalk.com/u/TheWonderful90s)\ **Post date:** [May 18, 2022, 11:21pm UTC](https://community.cartalk.com/t/fuel-economy-at-reduced-speed-calculating-cost-per-hour-savings/184195/27 "2022-05-18T23:21:46Z")
> [@Barkydog](#): > > I got 22 miles per gallon both situations based on miles and gas used. Do you have a trip computer or is this just estimated from fill ups at the gas station? A head wind or driving habits can be very significant. There should be some difference. Just calculating wind resistance alone would account for an increase in energy used (fuel consumed) by a factor 1.14. Of course it’s not all wind. There is some linear drag, and a gasoline engine increases its efficiency at higher load, so take 1.07 as the fuel consumption increase as a very rough guess. So 22 MPG ($0.182 per mile at $4 a gallon) should drop to 20.6 ($0.177 per mile) with that speed increase. Slowing from 78 ho 73 would save you $5.69 per hour of increased travel time at $4 gasoline. So it’s not worth it for you to slow down unless you’re poor. I wish I had real data to work with so I didn’t have to guess, since that figure is probably very inaccurate. ---
**Author:** ![asemaster](https://avatars.discourse-cdn.com/v4/letter/a/5f9b8f/32.png) [@asemaster](https://community.cartalk.com/u/asemaster)\ **Post date:** [May 19, 2022, 12:49am UTC](https://community.cartalk.com/t/fuel-economy-at-reduced-speed-calculating-cost-per-hour-savings/184195/28 "2022-05-19T00:49:24Z")
> [@TheWonderful90s](#): > > For most cars slowing down to less than 60 MPH isn’t going to save you money unless you bring home less than something in the ballpark of $12 per hour ??? Either it saves money or it doesn’t, which is it? My fuel economy is certainly not dependent upon my salary, is it? Should I ask for a pay raise or pay cut in order to use less gas? My commute from home to work is 44 miles door to door. This morning that drive took me 92 minutes. Monday it took me 55 minutes. Which was more economical? ---
**Author:** ![Barkydog](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/barkydog/32/2470_2.png) [@Barkydog](https://community.cartalk.com/u/Barkydog)\ **Post date:** [May 19, 2022, 1:01am UTC](https://community.cartalk.com/t/fuel-economy-at-reduced-speed-calculating-cost-per-hour-savings/184195/29 "2022-05-19T01:01:09Z")
> [@TheWonderful90s](#): > > Do you have a trip computer or is this just estimated from fill ups at the gas Sorry just miles and gas, starting full, fill up half way through and fill up at end, only 14 years experience with the TB. Have to check, but thinking 22 or so on tach at 65 mph and 22.5 at 78. ---
**Author:** ![VOLVO-V70](https://avatars.discourse-cdn.com/v4/letter/v/8e8cbc/32.png) [@VOLVO-V70](https://community.cartalk.com/u/VOLVO-V70)\ **Post date:** [May 19, 2022, 1:03am UTC](https://community.cartalk.com/t/fuel-economy-at-reduced-speed-calculating-cost-per-hour-savings/184195/30 "2022-05-19T01:03:34Z")
Trying to get good miles per gallon has nothing to do with a person’s hourly wage or cost per hour . ---
**Author:** ![TheWonderful90s](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thewonderful90s/32/29584_2.png) [@TheWonderful90s](https://community.cartalk.com/u/TheWonderful90s)\ **Post date:** [May 19, 2022, 1:14am UTC](https://community.cartalk.com/t/fuel-economy-at-reduced-speed-calculating-cost-per-hour-savings/184195/31 "2022-05-19T01:14:41Z")
> [@asemaster](#): > > Either it saves money or it doesn’t, which is it? My fuel economy is certainly not dependent upon my salary, is it? I explained it already, but if you didn’t read it then here it is again. If your travel time takes away time from your work, then you lose money don’t you? If you drive slowly and get to work an hour later, and you save $9 in fuel by driving slowly, but you lose making $15 in income after taxes (assuming your fuel is taxable income) by arriving to work late, then you actually lost $6 by driving more slowly. ---
**Author:** ![VOLVO-V70](https://avatars.discourse-cdn.com/v4/letter/v/8e8cbc/32.png) [@VOLVO-V70](https://community.cartalk.com/u/VOLVO-V70)\ **Post date:** [May 19, 2022, 1:21am UTC](https://community.cartalk.com/t/fuel-economy-at-reduced-speed-calculating-cost-per-hour-savings/184195/32 "2022-05-19T01:21:23Z")
> [@TheWonderful90s](#): > > but you lose making $15 in income after taxes (assuming your fuel is taxable income) by arriving to work late, You knucklehead just leave in time to get to work on time . I think another poster is correct , you are off your meds. ---
**Author:** ![Mustangman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/mustangman/32/44130_2.png) [@Mustangman](https://community.cartalk.com/u/Mustangman)\ **Post date:** [May 19, 2022, 1:34am UTC](https://community.cartalk.com/t/fuel-economy-at-reduced-speed-calculating-cost-per-hour-savings/184195/33 "2022-05-19T01:34:25Z")
> [@TheWonderful90s](#): > > If your travel time takes away time from your work Travel time generally takes time away from your leisure time, not your work time. Work is scheduled from 8 to 5 or 7 to 4 or whatever. Commute time is YOUR problem, not your employer’s. ---
**Author:** ![asemaster](https://avatars.discourse-cdn.com/v4/letter/a/5f9b8f/32.png) [@asemaster](https://community.cartalk.com/u/asemaster)\ **Post date:** [May 19, 2022, 4:00am UTC](https://community.cartalk.com/t/fuel-economy-at-reduced-speed-calculating-cost-per-hour-savings/184195/34 "2022-05-19T04:00:45Z")
> [@TheWonderful90s](#): > > explained it already, but if you didn’t read it then here it is again. If your travel time takes away time from your work, then you lose money don’t you? If you drive slowly and get to work an hour later, and Once again, I say my salary and my cost per mile have nothing to do with each other. The two have as much in common as a pig and a pair of pliers. If you showed up for work an hour late and said it was to improve your fuel economy, I would look you in the eye and say such nonsense will not be tolerated and further unexcused absence will result in termination. Who would ever think being late for work is an option? ---
**Author:** ![TheWonderful90s](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thewonderful90s/32/29584_2.png) [@TheWonderful90s](https://community.cartalk.com/u/TheWonderful90s)\ **Post date:** [May 19, 2022, 4:03am UTC](https://community.cartalk.com/t/fuel-economy-at-reduced-speed-calculating-cost-per-hour-savings/184195/35 "2022-05-19T04:03:05Z")
> [@asemaster](#): > > Who would ever think being late for work is an option? Have you ever done manual labor like painting or roofing for pay? Such work is often by the job. Get it done sooner and the next job starts sooner. ---
**Author:** ![Nevada\_545](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/nevada_545/32/41232_2.png) [@Nevada\_545](https://community.cartalk.com/u/Nevada_545)\ **Post date:** [May 19, 2022, 4:07am UTC](https://community.cartalk.com/t/fuel-economy-at-reduced-speed-calculating-cost-per-hour-savings/184195/36 "2022-05-19T04:07:48Z")
To leave earlier for work misses the point, time has value, on or off the company timeclock. If I arrive at work 20 minutes early, I expect to earn during that time. If I choose to work 2 extra hours after my schedule, I expect to be compensated for my time. I value my personal time the same way, to spend 45 minutes in traffic consumes my time, I might find a new route. During long trips I consider the time vs cost of the trip. When my employer pays for the expenses, I don’t drive 80 mph, that would be environmentally irresponsible. ---
**Author:** ![asemaster](https://avatars.discourse-cdn.com/v4/letter/a/5f9b8f/32.png) [@asemaster](https://community.cartalk.com/u/asemaster)\ **Post date:** [May 19, 2022, 4:10am UTC](https://community.cartalk.com/t/fuel-economy-at-reduced-speed-calculating-cost-per-hour-savings/184195/37 "2022-05-19T04:10:21Z")
> [@TheWonderful90s](#): > > Have you ever done manual labor like painting or roofing for pay? Such work is often by the job. Get it done sooner and the next job starts sooner. Certainly I have. Many years as a flat-rate mechanic, and I have worked under every pay plan under the sun. And being a business ownern is the ultimate “paid by the job” scenario. Your question simply proves my point. Once one of my flat rate guys came in at 930 instead of 8 and wondered where his 4 hour radiator job went. I calmly explained that if he didn’t want me to give his paycheck to someone else he should be here on time. But, once again, improving fuel mpg has nothing to do with your ability to be at work on time. The two exist independent of one another. ---
**Author:** ![Nevada\_545](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/nevada_545/32/41232_2.png) [@Nevada\_545](https://community.cartalk.com/u/Nevada_545)\ **Post date:** [May 19, 2022, 4:11am UTC](https://community.cartalk.com/t/fuel-economy-at-reduced-speed-calculating-cost-per-hour-savings/184195/38 "2022-05-19T04:11:23Z")
> [@TheWonderful90s](#): > > Have you ever done manual labor like painting or roofing for pay? Work like this begins billing when the crew arrives on the site, difficult concept. ---
**Author:** ![TheWonderful90s](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thewonderful90s/32/29584_2.png) [@TheWonderful90s](https://community.cartalk.com/u/TheWonderful90s)\ **Post date:** [May 19, 2022, 4:14am UTC](https://community.cartalk.com/t/fuel-economy-at-reduced-speed-calculating-cost-per-hour-savings/184195/39 "2022-05-19T04:14:03Z")
> [@Nevada\_545](#): > > To leave earlier for work misses the point, time has value, on or off the company timeclock. How does that miss the point? That is the point. If you leave 15 minutes early for work or get there 15 minutes later so that you can save $3 on fuel by driving slowly, but the job pays $16 per hour and you lost $4 of work during those 15 minutes that you could have been at work if you drove faster, then you actually lost $1 by driving slowly. Maybe you would rather be driving than doing your job, in which case it may be worth it for $1. ---
**Author:** ![Nevada\_545](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/nevada_545/32/41232_2.png) [@Nevada\_545](https://community.cartalk.com/u/Nevada_545)\ **Post date:** [May 19, 2022, 4:21am UTC](https://community.cartalk.com/t/fuel-economy-at-reduced-speed-calculating-cost-per-hour-savings/184195/40 "2022-05-19T04:21:09Z")
Saving fuel is not an excuse for arriving later for work. I was referring to this; > [@VOLVO-V70](#): > > You knucklehead just leave in time to get to work on time . I think another poster is correct , you are off your meds. [Previous page](https://community.cartalk.com/t/fuel-economy-at-reduced-speed-calculating-cost-per-hour-savings/184195.md?page=1) [Next page](https://community.cartalk.com/t/fuel-economy-at-reduced-speed-calculating-cost-per-hour-savings/184195.md?page=3)