What bikes are traditionally made of. There are lots of different grades of steel used for making bikes, from solid-but-heavy exhaust-pipe tubing to really high tech alloys which are extremely light and strong. Steel is going out of favour because all but the cheapest stuff is too thin for robots to weld – highly-skilled humans are needed instead. Good steel frames can still cut it with the best though. Steel has a bit more of a spring in it than aluminium – the ride will be less harsh. Steel frames will rust, but if looked after can last a lifetime – steel does not fatigue like aluminium.