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How do you figure out car's optimal speed...
- Thread starter AmadeusM
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I'm sure there is an optimal speed for your car, but imagine it's going to vary by vehicle, tire size, transmission, hp/weight ratio, and all that stuff.
So, I have no idea, but I've been driving like a grandma lately, even as low as 55-60 in a 70mph zone as long as it doesn't interfere with traffic. My mpg, which I check religiously, has gone from 14-15 to 17-18. Even got 19.3mpg on one fillup after traffic had allowed me to maintain 1800rpm/58-59mph consistently for a couple of days. I joined a Toyota forum, and they call it the rule of 2000--as in keep it under 2000 rpm.
A consumer report I read awhile back gave an average mpg of 13.9 for my truck(2001 Tundra 4x4).
I had a hard time believing it when I read that some people who lived where the speed limit was 55-60 were getting ~20mpg, but it works. I actually got worse mileage on the highway at my "optimal" speed (I call it MMS-maximum maintainable speed
) than I did driving around town. Not any more. It really doesn't add that much time to my daily commute, and these gas prices add some good incentive.
Being a bit of a speed demon by nature, I really miss the sensation of forward motion, though
So, I have no idea, but I've been driving like a grandma lately, even as low as 55-60 in a 70mph zone as long as it doesn't interfere with traffic. My mpg, which I check religiously, has gone from 14-15 to 17-18. Even got 19.3mpg on one fillup after traffic had allowed me to maintain 1800rpm/58-59mph consistently for a couple of days. I joined a Toyota forum, and they call it the rule of 2000--as in keep it under 2000 rpm.
A consumer report I read awhile back gave an average mpg of 13.9 for my truck(2001 Tundra 4x4).
I had a hard time believing it when I read that some people who lived where the speed limit was 55-60 were getting ~20mpg, but it works. I actually got worse mileage on the highway at my "optimal" speed (I call it MMS-maximum maintainable speed
) than I did driving around town. Not any more. It really doesn't add that much time to my daily commute, and these gas prices add some good incentive.Being a bit of a speed demon by nature, I really miss the sensation of forward motion, though
One thing is very critical in gas milage is wind resistance. The faster you go over 55 mph the more the shape of the vehicle is important. Most suv's and trucks have flat front ends that is like trying to move a box at high speed.
At 55-60 mph you are not generating neat the wind resistance that you will in the same car or truck at 70mph.
My other half, Karen drives a Honda Element. It has a very flat front end. When we drove down to Atlanta to visit family she got about 22mpg. We stopped for gas and I drove at an even 60-65mph compared to her 70-75. Filled up again when we got there and the Element got 26.8 mpg. Just 10 miles per hour made a differance of almost 5 miles per gallon. Now with gas getting expencive my lead foot wife can see the sence of driving a bit slower.
It's a combo of engine RPM and the wind resistance factor.
At 55-60 mph you are not generating neat the wind resistance that you will in the same car or truck at 70mph.
My other half, Karen drives a Honda Element. It has a very flat front end. When we drove down to Atlanta to visit family she got about 22mpg. We stopped for gas and I drove at an even 60-65mph compared to her 70-75. Filled up again when we got there and the Element got 26.8 mpg. Just 10 miles per hour made a differance of almost 5 miles per gallon. Now with gas getting expencive my lead foot wife can see the sence of driving a bit slower.
It's a combo of engine RPM and the wind resistance factor.
fracmeister
Petroleum Engineer
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One old rule is that how you use your brake determines your mileage. Obviously accelerating gently helps mileage, but when you brake you are wasting the kinetic energy that you have consumed potential (chemical) energy to create.
Even more important for those of us burning premium!
Even more important for those of us burning premium!
Gollnick
Musical Director
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- Mar 22, 1999
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- 29,258
In general, you will get the highest MPG when MPH / RPM is the greatest. So, find the speed that maximizes MPH / RPM. That will be the highest MPH at the lowest RPM.
You can think of the tachometer in your car as sort of a "rate of fuel use" guage. The higher the RPM, the faster you're burning your increasingly-precious gas. Drive in ways that keep your tach as low as possible and you will tend to maximize your MPG. The tach, by the way, is also a measure of engine wear. In general, the higher the tach is, the faster you're wearing out your engine. So, by keeping your tach low, not only will you maximize your MPG, but you will maximize the life of your gas-guzzler.
MPG stands for miles-per-gallon. The formula is MilesTraveled / GallonsOfGasUsed. Idling (0 MPH / some RPM) lowers your average MPG faster than anything else you can do by definition. You're burning gas, but not getting any distance. In general, to maximize MPG, when the engine is running, the vehicle should be moving. Do whatever you can to avoid standing still. For example, if you look a block ahead and can see that the light is red, slow down and try to pace yourself so that you arrive at the intersection just as the light turns green so that you don't have to stop. Encourage your city to time traffic lights so that you don't have to stop at every intersection. Encourage your city to replace four-way stops (the most energy-inefficient traffic control device) with traffic circles (probable the most energy-efficient traffic control device).
In general, you burn to most gas when you change speed, either when accelerating or braking. So, no matter what speed you're at, try to keep moving and keep moving at an even speed. Stop-and-go and speed-up/slow-down are the worst. Avoid that sort of traffic.
Your vehicle has two pedels, an accelerator and a brake. Pressing either one costs you money. Pressing the accelerator converts the gas you bought into kinetic energy (movement). Pressing the brake converts the kinetic energy you bought with your accelerator into heat which is uselessly dissipated into the atmosphere and lost. So, avoid pressing either one. It's that simple: avoid pressing either the accelerator or the brake.
You can think of the tachometer in your car as sort of a "rate of fuel use" guage. The higher the RPM, the faster you're burning your increasingly-precious gas. Drive in ways that keep your tach as low as possible and you will tend to maximize your MPG. The tach, by the way, is also a measure of engine wear. In general, the higher the tach is, the faster you're wearing out your engine. So, by keeping your tach low, not only will you maximize your MPG, but you will maximize the life of your gas-guzzler.
MPG stands for miles-per-gallon. The formula is MilesTraveled / GallonsOfGasUsed. Idling (0 MPH / some RPM) lowers your average MPG faster than anything else you can do by definition. You're burning gas, but not getting any distance. In general, to maximize MPG, when the engine is running, the vehicle should be moving. Do whatever you can to avoid standing still. For example, if you look a block ahead and can see that the light is red, slow down and try to pace yourself so that you arrive at the intersection just as the light turns green so that you don't have to stop. Encourage your city to time traffic lights so that you don't have to stop at every intersection. Encourage your city to replace four-way stops (the most energy-inefficient traffic control device) with traffic circles (probable the most energy-efficient traffic control device).
In general, you burn to most gas when you change speed, either when accelerating or braking. So, no matter what speed you're at, try to keep moving and keep moving at an even speed. Stop-and-go and speed-up/slow-down are the worst. Avoid that sort of traffic.
Your vehicle has two pedels, an accelerator and a brake. Pressing either one costs you money. Pressing the accelerator converts the gas you bought into kinetic energy (movement). Pressing the brake converts the kinetic energy you bought with your accelerator into heat which is uselessly dissipated into the atmosphere and lost. So, avoid pressing either one. It's that simple: avoid pressing either the accelerator or the brake.
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THe optimal speed on highway depends on your car's aerodynamics. As a rule of a thumb, faster you go on the last gear, more you consume. If your car has the best torque at 3000RPM, there is a good chance that your lowest consumption at constant speed is arround that value in the last gear.
When driving in the traffic, RPM's are not as important as not wasting energy. Try to "see ahead" when you have to slow down so you won't have to brake. Don't accelerate just for the hack of it (like when you know you'll have to slow down or stop at a light soon).
I recently tried how RPM's affect the consumption. I have a 2 liter diesel engine, 116 hp (Toyota Avensis SW). The max torque is at 2200RPM, and the courbe is quite flat from 1800 to 3000. When I drive at 2000 RPM on average when hitting constant speed, I get 35 MPG. When I drive at 3000 RPM on average when hitting constant speed, I get 34 MPG. There is almost no difference. If you have an onboard computer linked with the tachymeter and injection pump, the values it shows are quite accurate. If you push the accelerator the same, you consume almost the same at 2000RPM or 3000RPM. The injectors don't get more fuel even if the engine does higher RPM.
When driving in the traffic, RPM's are not as important as not wasting energy. Try to "see ahead" when you have to slow down so you won't have to brake. Don't accelerate just for the hack of it (like when you know you'll have to slow down or stop at a light soon).
I recently tried how RPM's affect the consumption. I have a 2 liter diesel engine, 116 hp (Toyota Avensis SW). The max torque is at 2200RPM, and the courbe is quite flat from 1800 to 3000. When I drive at 2000 RPM on average when hitting constant speed, I get 35 MPG. When I drive at 3000 RPM on average when hitting constant speed, I get 34 MPG. There is almost no difference. If you have an onboard computer linked with the tachymeter and injection pump, the values it shows are quite accurate. If you push the accelerator the same, you consume almost the same at 2000RPM or 3000RPM. The injectors don't get more fuel even if the engine does higher RPM.
silenthunterstudios
Slipjoint Addict
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Just clean your sparkplugs, make sure your tires are properly inflated. Not overinflated either. Make sure you don't fill up your tank while a new shipment is being pumped in, that stirs up all kinds of crap in the tanks that goes into your fuel supply, which could leave you stranded on the side of the road. Drive the posted speed limit. Don't stop and go, stop and go etc. If you can avoid gridlock, do so. Get rid of the lead foot. Be nice to your cars transmission. If you can carpool, do so.
Which is what I'm going to do as soon as this depression is over...
Which is what I'm going to do as soon as this depression is over...
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- Apr 20, 2004
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I seem to recall hearing about some student engineers at UC Davis that managed to get 100 mpg out of a stock Honda CRX. They kept it in 5th gear, letting it accelerate extremely slowly to 50 mph then shut off the engine and let it coast back down to like 15 mph, then restarted the engine and do it again and again.
Moral of the story: keep it in the highest gear possible without lugging the engine, be light on the gas, don't step on the brake, and keep speed to a moderately low rate.
Moral of the story: keep it in the highest gear possible without lugging the engine, be light on the gas, don't step on the brake, and keep speed to a moderately low rate.
Following too closely is also a great gas waster. Think about it. If you are close to the car in front of you, then you are likely constantly tapping your brakes when you feel yourself getting too close, then hitting the gas to maintain your interval. Back off far enough that you do not have to respond to his every action.
One of the most efficient ways to save money on gas is to avoid the unnecessary trip.
Another way to save money and to extend vehicle life is to always use the warm car, if possible. That is, if you come home from work in one vehicle and 30 minutes later have to run a short errand, take the vehicle that you just parked.
One of the most efficient ways to save money on gas is to avoid the unnecessary trip.
Another way to save money and to extend vehicle life is to always use the warm car, if possible. That is, if you come home from work in one vehicle and 30 minutes later have to run a short errand, take the vehicle that you just parked.
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brewthunda said:
Can I just point out that on the road that is a little bit dangerous as there is no power steering and no servo assistance to the brakes.
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AmadeusM said:
Tach driving for me. If you have a full-size vehicle get the rpm's up to 2,000 & try to maintain it,resisting urges to blast the fly-by-pull-in & brake bunch. We have a Yukon & Sierra & once you overcome the large flywheel inertia you are June-bugging . Our Yukon gets 20mpg & the truck almost 21mpg which I consider great for weight/horsepower/ protection ratio.
Works for me !
Uncle Alan
I lucked out and bought a Honda Odyssey Touring Edition a couple of months ago. It has an instantaneous MPG calculator, and keeps track of average MPG in between gasoline fills (it resets automatically with each fill). Even before the recent price spike I kept my eye on the calculator to learn the effects of my driving habits on MPG.
I get the best mileage between 60 and 65 mph. Long, painfully slow accelerations help conserve gasoline more than anything else, second would be getting off the gas pedal as soon as you're up to speed. In short, just drive like your vehicle is severely underpowered and you'll save significant gasoline.
Three of the six cylinders in my Odyssey are shut down by the computer in "economy" mode, which usually occurs at cruising speeds or when I let off the accelerator at city speeds. I can get up to 28 MPG on the freeways, but 25-26 is usually more like it. It's enlightening to see the effects of wind and elevation on consumption.
Twice I got in the mid-30s going from Cheyenne to Denver. I don't know if I had incredible tail winds or if I-25S loses elevation, but it was fun to see such high MPG. I bet it would not be nearly so high on the reverse trip.
I get the best mileage between 60 and 65 mph. Long, painfully slow accelerations help conserve gasoline more than anything else, second would be getting off the gas pedal as soon as you're up to speed. In short, just drive like your vehicle is severely underpowered and you'll save significant gasoline.
Three of the six cylinders in my Odyssey are shut down by the computer in "economy" mode, which usually occurs at cruising speeds or when I let off the accelerator at city speeds. I can get up to 28 MPG on the freeways, but 25-26 is usually more like it. It's enlightening to see the effects of wind and elevation on consumption.
Twice I got in the mid-30s going from Cheyenne to Denver. I don't know if I had incredible tail winds or if I-25S loses elevation, but it was fun to see such high MPG. I bet it would not be nearly so high on the reverse trip.
Let's take a look at a hypothetical acceleration to 60 and the gas mileage consumed over the first 30 seconds assuming 30mpg at 60mph:
Fastest my car can do it: 10 seconds. At that rate, I'm getting 3mpg during acceleration. My average mpg over 30 seconds is: 21mpg (3 * 10)+(20 *30)
Slow, but steady is 2 mph per second which will take 15 seconds. At that rate, I'm getting 8mpg. My average mpg over 30 seconds is 19. (8 * 15)+(15 *30)
If I really slow down and take a full 30 seconds to get to 60, I can probably get 15 from start to finish. Of course, my average would be 15mpg.
The point is: get up to the speed you're going to travel at as soon as you can and hold the speed. I'm comparing worst case economy to best in this scenario. In this scenario, flooring it is the way to go. If I redo the numbers for acceleration to 40, it wouldn't work out the same way, but loafing along and taking 2 minutes to get to speed is ALWAYS going to hurt your economy.
Fastest my car can do it: 10 seconds. At that rate, I'm getting 3mpg during acceleration. My average mpg over 30 seconds is: 21mpg (3 * 10)+(20 *30)
Slow, but steady is 2 mph per second which will take 15 seconds. At that rate, I'm getting 8mpg. My average mpg over 30 seconds is 19. (8 * 15)+(15 *30)
If I really slow down and take a full 30 seconds to get to 60, I can probably get 15 from start to finish. Of course, my average would be 15mpg.
The point is: get up to the speed you're going to travel at as soon as you can and hold the speed. I'm comparing worst case economy to best in this scenario. In this scenario, flooring it is the way to go. If I redo the numbers for acceleration to 40, it wouldn't work out the same way, but loafing along and taking 2 minutes to get to speed is ALWAYS going to hurt your economy.