If you aren't hanging them on an end wall, they can protrude a long way out into the space you are storing them in.
To get round this, I mounted some angle cut fence timber on the wall (Arris timber, I think it's called from Wickes) I then mounted the hooks to this, so the bikes sit at 45degrees to the wall.
It has improved things, but they still protrude quite a way into the garage, so I am considering bricking up the window in the end wall of the garage and moving them to that wall.
Another thing I did that I'd probably change was mounting the hooks at a height where the front tyre normally contacts the ground, rather than higher up the wall (where a straight line projected from the fork would reach the floor.
The front wheels tend to 'flip flop' side to side in the hook, whereas if the hook was in line with the projection of the fork this wouldn't happen.