My garage has a one inch thick wood shelf up high. I want to hang bikes below it. The bikes are heavy electric bikes, about 70 lbs each.
I bought J-hooks but I don't think that'll cut it. I've used toggle bolts with drywall before, do they have anything like that for 2x4s? Something that can drill through and expand on the other side of the shelf?
You can store bicycles vertically with the rear wheel resting on the ground:
You don't need to lift the bike to hang it
The fastener doesn't need to hold the full weight of the bike, only prevent it from falling over
Most of the weight rests on the floor, not hung on the shelf
Here's an example:
Your question is "How can I hang bikes under a thick wooden shelf?" (I point this out because others have proposed alternatives for bike storage that reduce but do not eliminate footprint by tilting it back and attaching the front wheel to the wall. If that would be sufficient for your situation, see "Alternative solutions" below.)
Now to your actual question:
First, I would note that a typical ¼" wood screw eye can hold 600 lbs or 300 kg, so if the wood is sound, you may use wood screw hooks. Still, I wouldn't want to stand under a 70 lb load with just one screw holding it. In fact, I wouldn't stand under anything while hoisting it, or ever if it didn't have at least two mounting points each capable of holding the entire load. That said, there are safe and reliable means to hang bikes overhead. For all of them, the substrate holding the weight must be sound (e.g., a sound 2x4 or joist; not drywall, plaster, etc.). I presume you are satisfied with the strength of your wood shelf; if not, post another question.
Now, to answer your specific question for something similar to an expanding toggle, that is, something that will spread the load over more of the wood:
You would use screw/bolt eyes (or hooks) with a machine thread, two flat washers, and two nuts. Thread a nut and washer onto the bolt, insert up through the hole you've drilled in the shelf, top with the other washer and nut, and tighten the nuts to squeeze the shelf. Some hooks have spring clips on the hook as well. The larger the washer, the more weight the wood can sustain; fender washers are larger and will hold plenty on a sound 1" board. The projection above the shelf need be no higher than the thickness of the bolt plus washer, so you lose little if any storage space.
Alternative solutions:
A swivel wall mount like this will hold over 66 lbs or 30 kg, is ready-made and easy to install, and will pivot to allow the bike to rest closer to the wall. You need not mount the bike with the rear wheel up off the floor as in the pic; I wouldn't want to lift it up there.
A bike hoist is a very elegant yet inexpensive solution that will screw directly to your shelf.
Its pulleys give a mechanical advantage of 4:1, so a 70 lb bike needs only an 18 lb pull, and it's pulling downward instead of lifting upward. The two brackets attach to the wood with eight included wood screws (providing plenty of redundancy). The rope lock holds the weight after each pull as you lift it, and stops the bike's descent if you let go.
