I talk for a while with Jon King of Corus, whose job it is to sell steel to car makers, and get the idea that aluminium car bodies are making some progress. The aluminium industry has claimed that usage of its material has grown to an average of 130kg per car. Jaguar XJ is all aluminium; BMW 7 is much more aluminium than it was; Mercedes S-class is a little bit aluminium. And what happens to the upper class trickles downs slowly to the working class does it not?

Then it occurs to me to ask where we are globally on the orders of magnitude: "That aluminium figure is largely aluminium blocks and heads displacing iron. On body structures we are reasonably comfortable. Sixty million vehicles are built every year with 99% of steel in the body structures." Ah. Not even close then?

There is some fuel and CO2 saving in an aluminium car. Jaguar shows that.

But the way that the CO2 fines will be imposed over the next new-model cycle life, there is little offset to be had from switching to lightweight material. Only a reduction of total mass is going to help in a measurable way. And if the carmaker takes the holistic view, additional energy used in aluminium production will cross-cancel the weight saving in its lifetime on a car.

There is increasing use of high tensile steels. Renault Laguna uses a lot of it. It's a bigger car but lighter. "The new Mondeo is a hell of a lot bigger, but if you do the calculation on the floorpan envelope it is lighter. There is a tide of vehicles coming which are lighter but use only steel. The Mazda 2 is lighter. So is Fiesta."

What else is there more cost-effective than steel in maintaining strength and reducing weight? Nothing it appears. The car that is imminent that is duty-bound to rewrite the rules is Tata Nano - due to sell at under GBP1,500 in India. Nano is steel intensive with a steel body structure. "I believe that they did look to see if they could have a radically simple structure. Fairly quickly they had to revert to a steel concept." Sounds to me that there is a degree of tactfulness in that "I believe" bit. Tata runs both Corus and the Nano project. You'd think that the King, the director of automobile engineering, might make the inner circle on this one.

Cars struggle for profit wherever you build them. They have to be cost effective. That flows all the way up to D-segment cars. On in the luxury class is there scope for lax spending. There is not much room for premium-priced structural materials lower down. And there is very little you can do about the cost of steel. The labour cost is small and pretty much fixed. Shipping cost precludes India serving Europe or Germany supplying Peru. It is only state-subsidised energy cost that can distort natural economics and that does not happen much.

All this scrabbling for 35kg here and there does seem a little futile though when you consider the role of the family car and the sort of people that some of them contain. There is not much scope for weight saving among my family members, but I suppose I could leave one of them at home or get Mrs G to pack fewer shoes. What would be the fuel saving Jon? "According to the numbers, a 10% weight saving gives a 5% to 7% fuel economy."

Sounds like sandals only love, and just one pair of 'em.

Rob Golding