Retention is the whole job
A cage has one thing to do: hold the bottle over rough ground without gripping it so hard you cannot get it out one-handed at speed.
Fibre-reinforced composite cages like the Elite Custom Race hit that balance well and are far more forgiving than aluminium, which bends out of shape over time and then either drops bottles or refuses to release them.
If you ride off-road, retention matters much more. A bottle ejected on a rocky descent is usually a bottle you do not get back.
Fitting, and the one warning
Nearly every frame has two threaded bosses on the down tube and often two more on the seat tube. The cage bolts straight on.
The one thing to be careful about is carbon frames — those bosses are bonded inserts, and overtightening can strip or damage them. Snug is enough. If you are unsure, we will do it in a minute at the shop.
Side-entry cages exist for small frames where a bottle cannot be lifted straight out. See water bottles for what goes in them.
