Weight vs gas mileage
Thread Starter
Cruising
Joined: Oct 2010
Posts: 11
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Weight vs gas mileage
I know none of us drive Corvettes for the mileage but I was talking to a friend tonight about making corvettes lighter when the mileage aspect came up. Our vettes are daily drivers so any time we get better gas mileage is a plus so I was wondering, does anybody have any idea if losing, say, 100 lbs would make a noticeable difference in gas mileage? I'm not hoping for 35 mpg or anything of that sort, just wondering if dropping 25/50/100 pounds might net me an extra few miles per tank during the week when I have to behave on the road. I know the weight loss pieces we might buy are for speed usually, just trying to find another perk, especially since 93 is creeping back up around $3 per gallon here.
Melting Slicks
Joined: Sep 2005
Posts: 2,568
Likes: 264
From: Near Charlotte NC
I find it hard to get good gas mileage from these cars because the temptation of the "right foot tickle" is too great.
However.......in May I made several runs from Charlotte,NC to Columbia,SC in 2 days.Driving the limit on every road I was able to average 34.3
\db2
carolina
(before you ask....YES it was boring driving a Z this way)
However.......in May I made several runs from Charlotte,NC to Columbia,SC in 2 days.Driving the limit on every road I was able to average 34.3
\db2
carolina
(before you ask....YES it was boring driving a Z this way)
Tech Contributor
Joined: Jan 2007
Posts: 19,476
Likes: 1,171
From: Dyer, IN
I know none of us drive Corvettes for the mileage but I was talking to a friend tonight about making corvettes lighter when the mileage aspect came up. Our vettes are daily drivers so any time we get better gas mileage is a plus so I was wondering, does anybody have any idea if losing, say, 100 lbs would make a noticeable difference in gas mileage? I'm not hoping for 35 mpg or anything of that sort, just wondering if dropping 25/50/100 pounds might net me an extra few miles per tank during the week when I have to behave on the road. I know the weight loss pieces we might buy are for speed usually, just trying to find another perk, especially since 93 is creeping back up around $3 per gallon here.
Tech Contributor
Joined: Jan 2004
Posts: 20,030
Likes: 289
From: Wylie TX --> Less is More, except under the hood !
It makes sense that loosing weight the MPG would increase...
That's why the C7 Corvette will have a 5.5 Liter motor, and the Corvette will be lighter. It will also likely be direct injection. It should make for a fuel efficient combo.
Its also about "weight to power ratio".
Just for example... My car is ~3100lbs, and I have ~525 crank HP. My weight to power ratio is 5.9. If the new C7 Corvette weighs 2800lbs, and has 475HP, the power to weight ratio will be the same, and thus the car should have the same acceleration as my car.
If the car makers can reduce the car's weight then they don't need to produce such high HP motors to get the same performance. They can put in a more fuel efficient motor with less HP and have the same performance as our heavier car's.
Hope that makes sense.
Did I go a little too far with my explanation ? My wife says I do that sometimes.
Toque
That's why the C7 Corvette will have a 5.5 Liter motor, and the Corvette will be lighter. It will also likely be direct injection. It should make for a fuel efficient combo.
Its also about "weight to power ratio".
Just for example... My car is ~3100lbs, and I have ~525 crank HP. My weight to power ratio is 5.9. If the new C7 Corvette weighs 2800lbs, and has 475HP, the power to weight ratio will be the same, and thus the car should have the same acceleration as my car.
If the car makers can reduce the car's weight then they don't need to produce such high HP motors to get the same performance. They can put in a more fuel efficient motor with less HP and have the same performance as our heavier car's.
Hope that makes sense.
Did I go a little too far with my explanation ? My wife says I do that sometimes.
Toque
Thread Starter
Cruising
Joined: Oct 2010
Posts: 11
Likes: 0
Thread Starter
Cruising
Joined: Oct 2010
Posts: 11
Likes: 0
It makes sense that loosing weight the MPG would increase...
That's why the C7 Corvette will have a 5.5 Liter motor, and the Corvette will be lighter. It will also likely be direct injection. It should make for a fuel efficient combo.
Its also about "weight to power ratio".
Just for example... My car is ~3100lbs, and I have ~525 crank HP. My weight to power ratio is 5.9. If the new C7 Corvette weighs 2800lbs, and has 475HP, the power to weight ratio will be the same, and thus the car should have the same acceleration as my car.
If the car makers can reduce the car's weight then they don't need to produce such high HP motors to get the same performance. They can put in a more fuel efficient motor with less HP and have the same performance as our heavier car's.
Hope that makes sense.
Did I go a little too far with my explanation ? My wife says I do that sometimes.
Toque
That's why the C7 Corvette will have a 5.5 Liter motor, and the Corvette will be lighter. It will also likely be direct injection. It should make for a fuel efficient combo.
Its also about "weight to power ratio".
Just for example... My car is ~3100lbs, and I have ~525 crank HP. My weight to power ratio is 5.9. If the new C7 Corvette weighs 2800lbs, and has 475HP, the power to weight ratio will be the same, and thus the car should have the same acceleration as my car.
If the car makers can reduce the car's weight then they don't need to produce such high HP motors to get the same performance. They can put in a more fuel efficient motor with less HP and have the same performance as our heavier car's.
Hope that makes sense.
Did I go a little too far with my explanation ? My wife says I do that sometimes.
Toque
lol nope, not too far, and pretty clear. I guess there's no real way of saying "if you loose x weight, you gain y mpg" too many factors involved maybe. I'm epicly bad at maths though so maybe there is a formula for it. As an example, with your car (hypothetical mpg here) 3100 lbs 525 hp and 27 mpg at 60mph. In that formula, what would happen with, say, 2950 lbs @ 525hp? 27.5 maybe? I'm not trying to be too serious with all of this, just trying to find another small benefit of being lighter
Race Director
Joined: Apr 2007
Posts: 11,152
Likes: 890
From: South Western Ontario
It takes a certain amount of power to accelerate the mass of the car from a stop to driving speed. Once at driving speed the weight really has no difference, it's the drag losses in the car that affect the mileage (aero drag, bearing drag, tire drag, brake pad drag, oil drag etc).
Remember F=ma (force = mass x acceleration)? It takes a certain amount of force to accelerate the mass. The force comes from the engine using fuel. Once the acceleration is done then this doesn't apply any more.
So, if you accelerate a lot then changing the weight will help the most with the fuel mileage. If you cruise on a highway a lot then changing the drag in the car will help the most with fuel mileage.
Peter
Remember F=ma (force = mass x acceleration)? It takes a certain amount of force to accelerate the mass. The force comes from the engine using fuel. Once the acceleration is done then this doesn't apply any more.
So, if you accelerate a lot then changing the weight will help the most with the fuel mileage. If you cruise on a highway a lot then changing the drag in the car will help the most with fuel mileage.
Peter
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Tech Contributor
Joined: Jan 2004
Posts: 20,030
Likes: 289
From: Wylie TX --> Less is More, except under the hood !
lol nope, not too far, and pretty clear. I guess there's no real way of saying "if you loose x weight, you gain y mpg" too many factors involved maybe. I'm epicly bad at maths though so maybe there is a formula for it. As an example, with your car (hypothetical mpg here) 3100 lbs 525 hp and 27 mpg at 60mph. In that formula, what would happen with, say, 2950 lbs @ 525hp? 27.5 maybe? I'm not trying to be too serious with all of this, just trying to find another small benefit of being lighter
Toque
Burning Brakes
Joined: Mar 2010
Posts: 1,189
Likes: 4
From: Freeport, FL
Good thought you have going.
It's too late for me to remember the technical terms, but focusing on rotational weight will yield a greater reduction in mass that needs to be moved and thus yield great weight reduction benefits.
Lighter wheels, tires, aluminum flywheel, etc. Even using the lowest tension valve spring for your application that still provides valve control can add a small benefit.
Problem is though, the cost of weight reduction is generally greater than the savings you receive.
Burning Brakes
Joined: Mar 2010
Posts: 1,189
Likes: 4
From: Freeport, FL
I know none of us drive Corvettes for the mileage but I was talking to a friend tonight about making corvettes lighter when the mileage aspect came up. Our vettes are daily drivers so any time we get better gas mileage is a plus so I was wondering, does anybody have any idea if losing, say, 100 lbs would make a noticeable difference in gas mileage? I'm not hoping for 35 mpg or anything of that sort, just wondering if dropping 25/50/100 pounds might net me an extra few miles per tank during the week when I have to behave on the road. I know the weight loss pieces we might buy are for speed usually, just trying to find another perk, especially since 93 is creeping back up around $3 per gallon here.
I had an 08 Wrangler with 28mpg and then traded for an 09 V6 Charger with 22mpg and traded that for my Vette with 25mpg, which I'm now happy with
hehehehehe screw the Prius, 25 average and 35 highway is good enough for me
Team Owner
Joined: Sep 2003
Posts: 43,084
Likes: 33
From: Raleigh / Rolesville NC
Over all wt should not change the fuel mileage too much. Unless your talking several 100 pounds.
☠☣☢ Semper Ebrius ☢☣☠
Joined: Jun 2001
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From: Virginia
Cruise-In IV-V-VI-VII Veteran
St. Jude's Donor '06
As was touched on previously, the mass of the vehicle does affect fuel efficiency, but only in certain ways. Remember that as you accelerate you are converting energy from one form to another. In effect, you transfer energy from the fuel to momentum (plus losses due to inefficiencies).
But you should also note that your momentum can also be either used or wasted. While you're cruising along the mass of your car doesn't matter--only drag does. When you climb a hill the mass does matter, but you're also building potential energy (through elevation) which can be converted back into kinetic energy (through gravity) as you go down the other side of the hill, thus saving you fuel. In this case more mass can be better as there will be more momentum to fight aerodynamic forces on the downhill side.
Real-world example: It takes a certain amount of energy to take your vehicle to the top of a hill, but you can get nearly all of that energy back as you descend the other side by turning off the engine. Now this obviously isn't safe, so the second best solution is to coast in neutral. Basically any momentum that is utilized to move your vehicle in place of fuel is energy used, as opposed to energy wasted through your brakes as heat.
But you should also note that your momentum can also be either used or wasted. While you're cruising along the mass of your car doesn't matter--only drag does. When you climb a hill the mass does matter, but you're also building potential energy (through elevation) which can be converted back into kinetic energy (through gravity) as you go down the other side of the hill, thus saving you fuel. In this case more mass can be better as there will be more momentum to fight aerodynamic forces on the downhill side.
Real-world example: It takes a certain amount of energy to take your vehicle to the top of a hill, but you can get nearly all of that energy back as you descend the other side by turning off the engine. Now this obviously isn't safe, so the second best solution is to coast in neutral. Basically any momentum that is utilized to move your vehicle in place of fuel is energy used, as opposed to energy wasted through your brakes as heat.
Safety Car
Joined: May 2008
Posts: 4,237
Likes: 11
From: Lacombe Louisiana
Mass has to effect fuel mileage.Say a 2000lb vehicle with 100 rwhp vs a 6000lb vehicle with 100 rwhp that has to use full throttle opening to maintain speed.The coast down theory would be the same for both vehicles,yet the vehicle with more mass would use more fuel.
Tech Contributor
Joined: May 2008
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From: Howell Michigan
St. Jude Donor '09-'10-'11
☠☣☢ Semper Ebrius ☢☣☠
Joined: Jun 2001
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From: Virginia
Cruise-In IV-V-VI-VII Veteran
St. Jude's Donor '06
It does take more energy to accelerate a greater mass. But you also have more momentum, so you can better recoup that energy. Turn off the engine on the 2,000 lb. vehicle and it'll come to a stop more quickly than the 6,000 lb. vehicle.
Put into practical use, this means that if you go climb a hill (using more fuel on the heavy vehicle) and then go into neutral on the downward side (using the same fuel for both vehicles), the heavier one will speed up more and go further before you have to shift into gear again and go above idle (using less fuel on the heavy vehicle.)
In overall real-life driving, with its starts and stops, winds, hills, curves, etc., the heavier vehicle tends to suffer because the greater energy which has been converted into momentum is wasted as heat, primarily through the brakes.
Burning Brakes
Joined: May 2008
Posts: 1,147
Likes: 1
From: Mohegan Lake New York
Good thought you have going.
It's too late for me to remember the technical terms, but focusing on rotational weight will yield a greater reduction in mass that needs to be moved and thus yield great weight reduction benefits.
Lighter wheels, tires, aluminum flywheel, etc. Even using the lowest tension valve spring for your application that still provides valve control can add a small benefit.
Problem is though, the cost of weight reduction is generally greater than the savings you receive.
Race Director
Joined: Apr 2007
Posts: 11,152
Likes: 890
From: South Western Ontario
The mass has no direct effect on the fuel mileage when moving at a constant speed on level ground. There are some small second order effects such as the heavier mass pushing the tires into the ground harder making them a little harder to rotate.
If you go for a highway drive with your can empty and then fill the trunk and back seat for the return trip you won't see much if any difference in fuel mileage unless you live in a hilly area. Hill climbing will cause a heavier car to use some extra fuel because more work has to be done to lift the mass of the vehicle by the height of the hill. Then, every engine and drivetrain has losses which means a certain amount of fuel is used even if the vehicle is idling as you come back down the hill on the other side.
So, the short answer is there is no possible way to relate the mass to the mileage. It will help but I'd believe 100lbs would barely even be noticeable. The amount depends on the vehicle and the driving conditions. Even the same vehicle driven the same route could show a mileage difference between 2 different drivers or on 2 different days.
Peter