I came across the below image today and thought it a great idea for storing bikes. However I wasn't sure if literally hanging a bike by its front wheel might cause undue stress to either the wheel itself or the front forks. Has anyone else done this to no ill effect? In the image below the back wheels don't even seem to be touching the floor, which I would have thought would take some of the weight.
You'd have to calulate the actual forces to be 100% sure but it's not going to be a problem: forces on front wheel/fork/headset while e.g. just sitting on the bike, braking or landing jumps will be (much) higher than the force applied from hanging it.
That being said, I do note at least two problems with this setup: first, good luck getting one of the center bikes out without touching or getting stuck in another bike. Second: from the picture it seems like you'd have to hold the bike with one hand then use the other to attach it. Ok for a roadbike, but for anything heavier that is just hard. Usually these systems have an open 'C'-shaped fixed hook into which you simply hang the bike which is much more convenient.
No, there are no problems with doing this.
Bike shops frequently hang bikes in a similar way.
And when I lived in small house in the inner city, I hung all of the family bikes in a similar way for years, without observing any problems.
It's remarkably easy to get the bike up onto the hook or peg, when you learn how. Those in the picture don't look as easy. The rack I built used big butcher's hooks.
Edit: Bike wheels are designed to carry the bike's weight plus up to 100 kg of rider. They work by the spokes being in tension, with the load distributed around the wheel. This Cyclingnews Maintenance & repair article shows the tension of the spokes for various rims. The minimum spoke tension from all the wheels in the list is 51 "kg force" (500 N). The maximum tension described is over 175 kg. Conclusion: hanging a 20 kg bike by the wheel is a non-issue, even if the load is carried by a single spoke.
I've done this before and it worked out nicely. I never had a problem with the forks (even with shocks, though if they are expensive shocks you'll want to lock them first), headjoints, anything. Turning them to face the wall (so its like they are riding up the wall) makes it easier to get them in and out. Even with a 40lbs. crappy, huge BSO-grade MTB it wasn't hard to stow or recover. Maybe my (tiny) wife would have found it more difficult, but anyway 40lbs. isn't very heavy* and its about as heavy as bikes get.
Not sure if I would do this with racing rims that have huge gaps between spoke sections, but then again a racing bike is ~1/3 the weight of a 40lbs. pile of poo -- so it probably wouldn't be an issue even then.
[*I mean 40lbs. isn't heavy to lift or carry... 40lbs. feels enormously heavy and sluggish to ride when you're used to slipping around on something 1/3 the weight!]