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http://www.hybridcars.com/gas-mileage-factors/cutting-weight-how-much-gas-does-it-save-0815.html

Cutting Weight: How Much Gas Does it Save?

Published August 15, 2008
Cutting Weight: How Much Gas Does it Save?

Traverse City, Michigan—The change in consumers’ car choices over the last few months has rocked every automaker, import as well as domestic.

Toyota’s Bob Carter illustrated the change yesterday with a single, stark statistic:

In May and June, more than 50 percent of the vehicles sold in the US were fitted with four-cylinder engines—for the first time in history, or at least since World War Two. <????>

But lost amidst talk of hybrids, plug-in hybrids, full electric vehicles, and techniques like gasoline direct injection, is a simple fact of physics: The greater the weight, the more energy it takes to move.
So what’s the actual impact of cutting weight? -

- The first study, conducted by respected British design and consulting firm Ricardo, looked at the fuel savings in different vehicle classes from reducing weight by 10 percent—while keeping performance comparable.

The study showed that a 10 percent weight reduction would cut fuel consumption 3 to 4 percent using the same engine.

But the savings rose to 6 to 7 percent if the engine was downsized for the lighter weight—and those numbers stayed constant across most vehicle classes, and applied equally to gasoline and diesel engines.
- A second study, from Ibis, then compared the cost-effectiveness of different tactics for reducing weight, comparing gasoline, diesel, and hybrid drivetrains in both steel and aluminum vehicles.

- With the steel vehicle as the baseline, increasing the aluminum content of the structure cost $44 per unit of mileage—but adding hybrid drive to the steel vehicle cost $259 per mileage unit, with a diesel engine coming in at $192. Combining an aluminum structure with the hybrid drive reduced the cost per mileage unit to $173, and it fell further to $104 with a diesel engine in the aluminum structure.
In other words, cutting weight may be a more cost-effective way to save fuel than adding hybrid-electric drive.-
Now think thru the rest of the vehicle dynamics ( and long term ownership costs) - once again battery hybrids are a fulltime loser - on all fronts.

Oh, and somebody get these two studies over to Mr Lutz.

At some point you have to start making a profit again so clearly 'spark ignition' plus weight reduction or diesel plus the same are much more attractive (44 - 104$ 'per mileage unit') than anything battery equipped ( 173 - 259$ 'per mileage unit') - except of course for a limited niche/green "pr halo" program.

Throw in some acceptable, smartly tailored small 'performance' trade offs .....
 

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I honestly thought cutting 10% in weight would save more than 3-4% in economy with the same powertrain. So basically if you lop off 400lbs from the G8 you would gain less than 1 mpg. I guess the performance advantage (accelerating, stopping, handling) of losing the 400lbs is a much bigger payoff.

I think this guy has a flawed perception as to how much it really saves.
 

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I could discuss weight/fuel economy in water craft but displacement resistance is so much harder on power than rolling resistance. Finding your engine's "Sweat Spot" does way more to conserving fuel than anything else load, etc.

But I do think his "flawed perception" does not take into account all the vairiables in driving. Stop and go driving, long HWY driving, Wind resistance, and payload. Dropping displacement will only hurt mileage while at Max payload, or heavy head winds.

I look back at selling C/K pick ups. a 2001 C/K with 3.73 gears actually got better milage than 1 with 3.42 ratio, even a 4.10 ratio did better. Why? The engine was in it's operating range and not "Lugging" around in every day driving.
 

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Oh, and somebody get these two studies over to Mr Lutz.
I couldn't agree MORE...
The new Camaro is the heaviest one EVER
The new STS (which is smaller then the car it replaced) was slightly heavier
Cobalt is heavier then a Cavalier
etc etc etc

Most GM cars (like me) need to go on a diet... The 3800-4000 pound Camaro confuses me... My third Gen Z28 weighs 3200 ponds has all steel body panels and a Cast Iron V8 block with Cast Iron heads, steel gas tank, etc etc... The new one has an all aluminum block and light weight body panels... etc etc and yet it is about 500 pounds heavier.
 

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I couldn't agree MORE...
The new Camaro is the heaviest one EVER
The new STS (which is smaller then the car it replaced) was slightly heavier
Cobalt is heavier then a Cavalier
etc etc etc

Most GM cars (like me) need to go on a diet... The 3800-4000 pound Camaro confuses me... My third Gen Z28 weighs 3200 ponds has all steel body panels and a Cast Iron V8 block with Cast Iron heads, steel gas tank, etc etc... The new one has an all aluminum block and light weight body panels... etc etc and yet it is about 500 pounds heavier.
Because people wanted all these's electronic goodies, and a lot of airbags in there car's.
 

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Vehicle weight isn't really THAT big of an issue if the car has a properly set up powertrain, which I find GM has a bit of an issue with as far as gearing is concerned.

First you need a decent number of gears. 4 really isn't enough if you're after really good mileage. Now the sad part is that GM and Ford spent a ton of cash to develop a 6 speed auto when they could have turned their 4 speed into an 8 speed auto fairly easily.

A simple 8 speed transmission from a heavy truck is really only a 4 speed tranny with a gear on the output shaft. you shift gears 1-4, flip the output shaft into high range and start over again from 1-4 ( now 5-8 ).

GM and Ford could have done the same thing by throwing a planetary gear on the output shaft of their transmissions and voila, an 8 speed tranny that's a lot smaller and lighter than that 6 speed monster they just came up with. They could have made an even smaller still 6 speed from a 3 speed auto, with fewer gears, clutch bands and fluids etc.

With more gears, the engine doesn't have to rev as high during acceleration because your gears are closer together. Smoother, quieter more fuel efficient acceleration is the result. More gears would have been an absolute blessing to GM's older, torquey OHV engines.

Now with more gears you can also have basically an overdrive gear for cruising at city speeds, with the engine turning low rpm ( 1200 - 1500 range) and letting torque move the vehicle, until you need more power or speed and the tranny downshifts a gear into the engine's power band. Once the need for more power is gone, say you finished running yet another yellow light, then the transmission can upshift into it's cruising gear.

You get the transmission set up this way as well for the highway and basically what your looking at is having your car moving 40mph in the city, but turning the same rpm as if it were going 30, and on the highway going 65mph with your engine working as if you were driving 50mph.

It also makes it possible for GM to focus on making their engines more efficient across a smaller, more specific rpm range.

Sorry for the long post, I just figured some explanation was better than a simple " GM can't gear worth a darn " post :)
 

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After dropping about 120 lbs. from my '97 SC2 and 60 lbs. off myself, my average mileage between fill-ups went up about 3 mpg. Then again, 180 lbs. off a sub-2,500 lbs. car is more than off of say... a 4,000 lbs. car such as the G8.
 

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In other words, cutting weight may be a more cost-effective way to save fuel than adding hybrid-electric drive.-
This is hardly news. E.g. BMW and Mazda are actively working on that for some time. The new Mazda 2 and 6 are both larger and LIGHTER than their predecessors, achieving impressive fuel economy (not sure about the USDM Auto Alliance 6 sedan, though). GM is hopeless when it comes to lightweight engineering, their solution to fix something is to ADD stuff, for example one of the reasons the Aveo is a heavy gas hog is the copious sound insulation inside to counter the body-induced wind noise, rolling noise, suspension clunks and of course the sweet sound of Family 1 engines.
 

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In other words if you weigh over 200 lbs you shouldn't be able to buy a Camaro. But if you weigh less than 150 lbs.... they will give you credit for 50lbs in rewards weight !!
Kind of like back in the old Trans Am Gen1 days when the Penske Camaros were actually a couple of hundred pounds too light and they were always looking to cleverly conceal 200 lbs of weight before tech inspection.
I guess knowing this shows my age and I shouldn't be allowed to buy another one either.
 

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Vehicle weight isn't really THAT big of an issue if the car has a properly set up powertrain, which I find GM has a bit of an issue with as far as gearing is concerned.

First you need a decent number of gears. 4 really isn't enough if you're after really good mileage. Now the sad part is that GM and Ford spent a ton of cash to develop a 6 speed auto when they could have turned their 4 speed into an 8 speed auto fairly easily.

A simple 8 speed transmission from a heavy truck is really only a 4 speed tranny with a gear on the output shaft. you shift gears 1-4, flip the output shaft into high range and start over again from 1-4 ( now 5-8 ).

GM and Ford could have done the same thing by throwing a planetary gear on the output shaft of their transmissions and voila, an 8 speed tranny that's a lot smaller and lighter than that 6 speed monster they just came up with. They could have made an even smaller still 6 speed from a 3 speed auto, with fewer gears, clutch bands and fluids etc.

With more gears, the engine doesn't have to rev as high during acceleration because your gears are closer together. Smoother, quieter more fuel efficient acceleration is the result. More gears would have been an absolute blessing to GM's older, torquey OHV engines.

Now with more gears you can also have basically an overdrive gear for cruising at city speeds, with the engine turning low rpm ( 1200 - 1500 range) and letting torque move the vehicle, until you need more power or speed and the tranny downshifts a gear into the engine's power band. Once the need for more power is gone, say you finished running yet another yellow light, then the transmission can upshift into it's cruising gear.

You get the transmission set up this way as well for the highway and basically what your looking at is having your car moving 40mph in the city, but turning the same rpm as if it were going 30, and on the highway going 65mph with your engine working as if you were driving 50mph.

It also makes it possible for GM to focus on making their engines more efficient across a smaller, more specific rpm range.

Sorry for the long post, I just figured some explanation was better than a simple " GM can't gear worth a darn " post :)
Valid points, but don't you think that at least one of the Ford or GM engineers would have thought of this along the way? I'm sure they've heard about Gear Vendors. There has to be a reason why nobody does this in a light vehicle, let alone a 3/4 or 1-ton truck.
 

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Actually not that great example... I was looking at BMW R1150RT's and they burn about the same gas as a Toyota Echo!:eek:
Yeah, I'm betting there are a lot of examples of motorcycles with poor mileage due to large engines and tons of power, but when a motorcycle's engine is sized to give the power to weight ratio of a normal car, things look a lot different.
 

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Valid points, but don't you think that at least one of the Ford or GM engineers would have thought of this along the way? I'm sure they've heard about Gear Vendors. There has to be a reason why nobody does this in a light vehicle, let alone a 3/4 or 1-ton truck.
It is certainly possible that one of their engineers thought about it, but I wouldn't be surprised if they didn't either. Sometimes when I have a problem with a car / truck / appliance etc the most complicated solutions come to mind and it turns out to be stupidly simple. (ie I've a friend who couldn't figure out why his dash backlight wasn't on. First thing he did was go for the fuses instead of checking the dimmer switch which was turned all the way down. )

I've also noticed they missed an easy way to get better city milage. For example when cruising at city speeds (60km) my chrysler vehicles with their 4speed auto will drop into the overdrive gear and let the engine's torque move the car around, usually at 1200 rpm. On my GM vehicles however, they all want to sit in 3rd and run the engine at 2000 rpm and wont take the next, more fuel efficient gear until 65 - 70 km/h, at which point I'm over the speed limit. Not only that but my GM vehicles will downshift needlessly back into 3rd when I'm cruising on flat ground.

Because of the way the vehicles are geared, I can get very very close to the same mileage from my '97 Intrepid 3.3L V6 as my '00 Cavalier 2.2L I4, both with auto trannies. With my friend's 98 Cavalier 5spd I can get much better fuel economy at city speeds cruising around at the bottom of 4th gear.

They missed that easy trick for decades, unfortunately. I can understand why it wouldn't have been done up to this point as well though. It was unnecessary. Gas was cheap, we were and still are addicted to power, it made more sense to keep the tranny simple and reliable and let the engine do the work. Who doesn't love listening to an engine growl when you pass someone on a country road ? It's like a mad max flashback for 10 seconds:cool:.

Then there's the possibility that the big 3 figure we just don't need it. It wasn't until the competition started droping 5 speed autos in their cars that GM and Ford bothered to look into something better than their 4speed trannies. Why do we still have FWD vehicles on the GM showroom floor with solid axle suspensions and drum brakes in the rear ? Because GM figures we don't need any better and they can make a bit more money per vehicle by giving us the old stuff... Drum brakes ! :rolleyes:
 
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