Originally Posted by mangochutney
That one's got me interested. What kind of alloy is it? Or else, how is it treated to achieve such qualities? Got a link, I'm curious.
Just general bog standard steel is around 3 times stiffer than aluminium. Most steels are equally stiff. There's a list on wikipedia...http://en.wikipedia.org/wiki/Young's...oximate_values
However, something nice like Reynolds 853 (or even the drool worthy 953 stainless version) has a tensile strength about 50% more than cheaper stuff like 4130 ChroMo steel. Stength to weight ratio on 853 approaches Titanium but it's stiffer.
When you're building bicycles, you're not generally worried about how big in diameter the tubes are though so lighter, less stiff, less strong materials like carbon fibre and aluminium can be used and even though the tubes are larger in order to maintain rigidity, they usually weigh less than steel or titanium. Aluminium has to be alloyed with other metals otherwise it's way too brittle to have any kind of life or you have to build a frame with so little give in it that the frame doesn't flex at all. Think of the difference between a Coke can and a Heinz Beans can. The coke can is lighter but less stiff. If you wanted the same stiffness from steel it still wouldn't be as light as aluminium though. The coke can on the other hand to be as stiff as steel would be very thick.
Some of the Reynolds 853 tubes are as thick as 0.5mm in the middle yet you're talking about a mountain bike that'll take all the abuse given out by an average trail rider and it's stronger than much thicker aluminium tubed bikes and suffers less from dents and dings from rocks.http://www.reynoldscycles.co.uk/steel853.html
Unusually, it also hardens in air after welding which means you don't have to go reinforcing your weld areas with gussets, giving more weight savings.
For such an old material, there's still advances in alloying happening that don't quite count it out yet.
Again, it'd be an interesting choice for laptop use and I'd guess steel's other characteristics over-rule the material benefits.
With aluminium there's also a huge amount of work making stiffer and more fatigue resistant alloys which is why every year bikes seem to get lighter and more reliable. 6069 Alumnium in the last few years has pushed what you can do with aluminium to places I'd not thought possible.
I don't know what grade aluminium Apple use but to me it doesn't seem like they've got a bike nut looking after their materials choice.