The car manufacturers have a problem that on the face of it, doesn't seem to have an easy solution, writes Andrew Hamilton.
Their customer base want faster and bigger cars which means heavier cars and more tax. The engineers, on the other hand, need to get the weight down. There's only solution and that means using a more lightweight construction material than steel.
Jaguar engineers believe they are pointing the way forward, replacing steel with aluminium in their new XJ flagship model, due to be launched here in the spring.
Aluminium has been around before and Jaguar says its aluminium "vehicle" was away back in 1922. More recently Audi has used it in a widespread way in models such as the A2 and the A8.
However, Jaguar claims that the aluminium bodyshell in the new XJ goes further. It weighs just 220kg while the steel equivalent is 360kg.
This weight loss gives it an advantage over competitors. Take the XJ 3.5 compared with the BMW 735i, both of which are V8. The British car is 245kg lighter on the scales.
As well as being up to 200kg lighter than its predecessor, the new car is longer, taller and wider.
With a body that is 40 per cent lighter but 60 per cent stiffer, the new XJ promises to be a major player in the luxury car sector next year. It goes on Irish sale in March or April and we will have to wait until then for pricing details.
Aluminium construction is more expensive than steel so the big question is just how much will that impact on the pricing.