Unsustainable bicycles

To make what is meant by a sustainable bike clearer, here is what makes a bike unsustainable:

Non standard parts

If you can't get spare parts, then the bike is no good. This is mostly a problem at the extremes of the market, with very cheap and very expensive bikes often having non standard parts. Folding bikes can be problematic too.

Examples of things that are hard or impossible to find are:

22 inch tyres

26 x 1 1/4 rims

Anything with French threads

122 mm bcd chainrings

6 speed freehub sprockets

Shimano positron gear parts

any bottom bracket that is not standard square or cottered

Poor quality of threads.

These are the bits you can't see unless you pull the bike apart. If the metal in the frame is not good, or the tool used to cut the thread is worn, then the bike will fall apart and be irreperable.

A very cheap bike is essentially disposable, as the cost of repair quickly exceeds the replacement cost. The supermarket £99 specials are a waste of raw materials.

Aluminium and carbon fibre frames will fail. Aluminium has a fatigue life, and after perhaps 10 or 20 years it will fall apart. This happens to anything made of aluminium. It turns white and crumbles eventually. Old aluminium bikes are very rare.

Carbon fibre can be made into wonderful racing frames, but these are not meant to last. Carbon fibre forks should be replaced every 2 years, or what the maker recommends. Carbon fibre also splinters like wood in a crash.

Titanium should be a perfect material for bike frames, as it has a very long fatigue life and doesn't corrode. Unfortunately it is very difficult to work with and not all Ti frames are made as well as they could be. Therefore they break. It's also not that much lighter than steel.