A weighty issue for auto efficiency

Cutting vehicle weight may be the next main advance in reducing the financial and environmental cost of motoring.

Until now carmakers have met a trend towards tougher fuel economy standards worldwide by reducing engine sizes and introducing technology, for example to cut motors when a car is idling.

In the next step up, choices include electric and hybrid power technologies but these add thousands of dollars to the upfront cost of a vehicle.

By contrast, recent US studies have shown that cutting vehicle weight can improve efficiency while reducing manufacturing costs, where the higher cost of lighter materials is offset by less bulk and lower labour costs.

That synergy was summed up by the International Council on Clean Transportation (ICCT), a research group, in a report it published in January: "Summary of mass reduction impacts on EU cost curves".

"Since less energy is required to move a reduced mass, the vehicle engine can be downsized. Similarly, components such as the vehicle suspension, brakes, and body can be made smaller or lighter since they need not support the same mass or dissipate the same energy."

One hurdle to adoption in Europe has been a policy where carbon emissions reduction targets are assigned by weight, applying more ambitious cuts to lighter vehicles, potentially wiping out the benefit towards meeting targets from shedding pounds.

That is changing, slowly.

One alternative is to classify cars by the area they physically cover, which would allow manufacturers to maintain their diversity of models while capturing the benefit of lighter materials.

A panel of European Parliament lawmakers on Tuesday approved a choice of footprint or weight parameters from 2020, giving manufacturers a choice in how they apply targets. That contrasts with the European Commission which has proposed a review of a footprint approach after 2020.

Options

The US Environmental Protection Agency has commissioned various studies to measure the incremental manufacturing cost of reducing vehicle weight.

For example, FEV Inc, a designer of conventional and alternative transportation energy systems, undertook a so-called teardown analysis of a 2010 Toyota Venza for a study, "Light-Duty Vehicle Mass Reduction and Cost Analysis – Midsize Crossover Utility Vehicle", published last August.

The Venza was chosen as an example of a new model which was typical of the crossover utility type and with the latest safety aspects.

The analysis involved tearing apart a vehicle to its individual components and then estimating the incremental manufacturing cost of substituting these for lighter alternatives.

The original weight of the vehicle was 1,711 kilograms (kg) and the target for mass reduction in the analysis was 20 per cent, or 342 kg.

The purchase price of the vehicle was $25,063 and the estimated direct manufacturing cost was $16,709.

The FEV study concluded that the optimum mass reduction was 312.48 kg, or just under a fifth of the total vehicle weight, because that could be met with a manufacturing cost saving of $148.06.

It found that costs turned positive for greater weight reductions.

The cost savings were made through offsetting an increase in material costs with cuts in labour costs and manufacturing overheads and a mark-up saving.

Weight reductions were met both by downsizing parts and using different materials, such as aluminium or plastic instead of iron or steel.

The weight reductions were mostly in the body system, at 4 per cent of the total saving; the suspension system (3.91 per cent); the interior (2.45 per cent); and the braking system (1.91 per cent)

Safety

One common argument against using lighter weight materials is a feared compromise on vehicle safety.

In a parallel study to that of FEV, the engineering arm of lightweight vehicle manufacturer Lotus suggested that there was no such sacrifice, in a report commissioned by the California Air Resources Board (ARB) and published last August.

The study was titled "Evaluating the Structure and Crashworthiness of a 2020 Model-Year, Mass-Reduced Crossover Vehicle Using FEA Modeling".

It performed car crash simulations to measure the effect of reducing vehicle weight by just over 30 percent, designing a new model based on the 2009 Toyota Venza according to vehicle dimensions, utility objectives, and passenger and interior volume.

"The theoretical study indicates that a low-mass body structure has the potential to meet Federal Motor Vehicle Safety Standards (FMVSS) for light duty vehicles for front, side, and rear impacts, roof crush, occupant restraints and several Insurance Institute for Highway Safety requirements," it concluded.

Carbon saving

The International Council on Clean Transportation (ICCT) is an international research firm which supplies technical and scientific analysis to environmental regulators.

It recently applied such mass reduction studies to analyse the cost impact of meeting EU carbon emissions targets by cutting vehicle weight.

ICCT published a study in January which analysed the extra cost for manufacturers to cut carbon dioxide emissions in line with the proposed EU 2020 target (95 grams CO2 per kilometre) compared with a 2010 baseline.

They found that compliance costs under a regulatory system which credited weight reduction, such as a footprint approach, were as much as half as an alternative approach which penalised weight reductions.

"Compliance costs are much lower under a regulatory structure that fully credits the CO2 emission reduction benefits of vehicle mass reduction than under a structure where mass reduction technologies are not fully creditable," it found in its January report.

Such findings suggest that the EU might move faster to base its fuel economy targets on a choice of footprint or weight.

- Reuters