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When I choose a material for a bike frame, I have to

think about the properties of the material. How elastic

Ís it? If you bend or stretch it, will it go back to its

original shape? If it does, it has high elasticity. How

strong is it? There are two kinds of strength. The first is

how much force you need to bend it to a point where it

can't go back to its original shape. The second is the

amount offorce you need to break it.

Steel is the least expensive choice. There's a wide range

of standard gauge tubes available. It's strong and it has

good elasticity but it's heavy.

Aluminium is lÍght and strong but it,s flexible. The

more it bends, the quicker Ít breaks. So aluminium bike

frames use large diameter tubes. That limits the

amount of bending.

Titanium has a great strength.to.weight ratÍo. It,s got

good elasticity so when it bends it tends to return to its

original shape. It's corrosion-resistant so you don,t

need to paint it. But it's expensive

- fifteen times the price of steel!

The professÍonals use carbon

fibre. It's very light and it's very

strong. You can shape it any way

you like. But carbon-fibre

frames are hand-made

so they're very

expensive