You are very correct Shaun.
The story is similar to the endless hydrogen vs oil debates where people forget about the energy required to make the hydrogen.

Quite possibly the future may be carbon in the form of carbon fibre and its many brothers the carbon nano tubes and various nano structure designs. Virtually the whole vehicle can be made of carbon.
The stuff is very light by nature, but it can be made impossibly hard and impact resistant or flexible and soft. The chasis could be carbon as could the engine/fuel cell, fuel storage tank, lubricant and any fabric like material within the vehicle. Even the tires can be manufactured of the stuff.
And when you recycle your car it gets liquified completely into one element by some process, ready to be turend into something else. I could be wrong, but it sounds too elegant to be rubbish.

Out of interest, I loaded a Toyota Prius simulator with the following data points:

Ambient Temperature: 70°F or 21°C
Wind: None
Barometer: 30.03 in/Hg or 101.7 kPa
Relative Humidity: 85%
Elevation: 410 ft. or 125 m
Vehicle Speed: 70 MPH or 112.65 km/h
Total Vehicle + Cargo Weight: 3,100 lbs or 1,406 kg

The simulator shows that the Prius would get 49.21 MPG(US) or 20.92 km/l or 4.78 L/100 km

I then removed 500 lbs or 227 kg from the vehicle. In reality, it would be very difficult to find enough steel components that could be converted to aluminum or aluminium to get a net savings of 500 lbs or 227 kg & almost puts this example into the realms of ‘unreality’ but, let’s take a look now at the fuel savings anyway.

Eff w/ normal weight............Eff w/ weight reduction
49.21 MPG.......................50.72 MPG
20.92 km/l..........................21.56 km/l
4.78 l/100 km....................4.64 l/100 km

So, on a 62.14 mile or 100 km journey this vehicle will save 0.038 gallons(US) or 0.11 liters with 500 lbs or 227 kg removed.

The article only uses 100 kg or 220 lbs reduction so, I will now adjust this commentary’s numbers to make them relative to the article.

A very important baseline in this article’s study states: “0.35 liters of fuel saved per 100 km per 100 kg weight reduction.”

The example I cite in this commentary indicates that the savings on a Prius would only be 0.05 liters of fuel saved per 100 km per 100 kg weight reduction.

This means that a very fuel efficient vehicle like a Prius only stands to save 14% as much whatever this article is using as a baseline vehicle fuel efficiency.

This tells us that it is far more beneficial to pursue CO2 reduction by using hybrid vehicle technology than it is by simply reducing a vehicle’s weight with aluminum or aluminium.

Wayne -

bear in mind that the drive cycles used to calculate official fuel economy numbers all feature only moderate acceleration and no hill climbing at all. Yet those are the real-world situations where additional mass really does impact fuel economy. If you live in hilly terrain, consider buying the lightest car that meets your requirements.

Even so, aluminium, for all its advantages, is no miracle material in coachbuilding. In particular, Audi discovered the hard way with its now-discontinued A2 that it's hard to achieve the necessary geometrical tolerances using aluminium sheetmetal. The hood and trunk lid are more forgiving parts in that respect than the doors and fenders, which often require expensive manual post-processing to meet spec.

The material is great for many drivetrain parts and housings, including the suspension and wheel rims. It also performs well for certain parts of the monocoque chassis. For these applications, the metal is typically cast or kneaded (e.g. forged, extruded or hydroformed).

Porsche and others (e.g. BMW) have experimented with carbon fiber body parts in series production vehicles. However, the EU mandates that vehicles be designed for recycling. Given the still sky-high cost of carbon fibers, that means dissolving the matrix and recovering the fibers. The process tends to shorten the fibers, making them unsuitable for the same application. Therefore, in spite of the undoubted technological advantages of composites for small production runs, their intensive use remains limited to race cars.

This would change IFF carbon fibers were to become cheap enough to permit the incineration of composites for electricity generation at the end of their life. Lignin, a waste stream in wood processing, is a viable feedstock though it is hard to handle as it is a natural glue. Either solar ovens and biogas could be used to provide the energy required for the high-temperature pyrolysis process. Another "carbon-neutral" source of process energy would be the vast amounts of associated gas that are flared off near oil wellheads, mostly in Russia, Africa and the Middle East.

Could you please link to the study? There is no link to follow from the underlined word "determines" in the first line. Thanks.

Hi Harvey & Rafael,

First, in answer to Harvey; yes, aerodynamics does play a big part in the formula. At 70 MPH the aerodynamic drag consumes 10.75 kW or 13.51 horsepower. At 25 MPH it consumes 0.46 kW or 0.62 horsepower.

At 25 MPH a reduction of 100 kg or 220 lbs will increase the MPG from 99.14 MPG 101.57 MPG. This constitutes a 2.4% gain in MPG whereas at 70 MPH we are only getting a 1.3% gain. However, even though it would appear that I am saving significantly more at 25 MPH, I am, ironically, still saving exactly 0.05 liters of fuel per 100 km per 100 kg weight reduction. Again, hybrid technology wins hands down in slow speeds also when it comes to reducing CO2.

The simulator does take into consideration high voltage battery SOC (state of charge) averaging for such speeds. The Prius actually does better in city mileage than highway so, much of the gain that would otherwise be available in 'normal' or non-hybrid vehicles does not apply in a series/parallel hybrid like the Prius.

In response to Rafael's comments: The Prius pulls away from a dead stop using mostly electrical energy it has captured from regenerative slow-downs & braking. Even when the ICE or internal combustion engine comes to life when pulling away from a dead stop, it generally contributes less than 15% of the motive forces up to 20 MPH so, most of the energy used to start out is from energy captured via regeneration while slowing down or braking.

As for mountains; most Prius owners have found that they do not lose any mileage in mountainous terrain but, actually come out slightly ahead of flat terrain MPG. Many opinions have been offered over the years on this & much has been opined on this throughout most of the groups but, overall it has mostly to do with downhill regenerative energy capturing. I have added an extra 18 Ah of high voltage battery for a total of 24.5 Ah vs. OEM of 6.5 Ah & seem to do significantly better in mountainous terrain than do my fellow Prius drivers.

All that said though, you are correct Rafael; we would need smaller storage batteries & less powerful engines in our hybrid vehicles if we were to make them with less mass. However, a whole lot less CO2 would enter the atmosphere if the same $ being spent on weight reduction by using aluminum parts were to be spent instead, in converting production lines to fabricate hybrids such as the Prius.

...and then what of the CO2 produced in the production of hybrid components versus a non-hybrid lightweight vehicle?

Yeah, the trick is to buy a used Prius and let the first owner do all the dirty driving. :-)

Of course this means that a second hand Prius should be worth more than a new one!

The sad thing about automobiles is that even though more and more components are made out of light-weight plastic or aluminum, the later-model cars on average are getting heavier and heavier. More and more engine improvements in power and efficiency are achieved, but, instead, these are neutralized by the quest to make the cars bigger, heavier, and faster! CAFE has not seen much improvement in 20 years!

MIND OVER MATTERS! If the will to produce light-weight and fuel-efficient cars is not there, it ain't gonna happen.

just quit fighting over which material is best.. I just say aluminium is the next logical material hands down. ALCAN just got bought by Rio Tinto. The real issue with aluminium is not workabilty but availabliity. Only one pound of aluminium is mined, refined, smeltered for every 30 pounds of iron/steel mined and produced in this world. A ratio of 30 to one is obviously lopsided. It should be more like 4 to one or better. We certainly dont need aluminium to build skyscrapers and bridges and train rails. But we will still need three times present production of aluminium to satisfy automobile production alone when extensive usage of aluminum is required to boost fuel conservation as well as carbon reduction in the atmosphere.

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