Originally Posted by SDS

Your toes should not touch the front of the shoes. On a long ride your feet can swell and push the toes farther into the front of the shoe, and your toes will buckle and get scuffed on the inside of the shoe, and that hurts. Also, pushing the nail on the toe into something hurts, and you can lose the nail, which also hurts. You can't support a load pushing forward on your toes for long.

Feet are like wedges. The function of the fastening system on the shoe over the top of the instep is to hold the "wedge" back, so your heel stays in the heel of the shoe and your toes stay away from the front of the shoe.

Ideally, cyling shoes have a tall, wide toe box, with room to wiggle the toes and are perfectly fitted everywhere else. If you are healthy and you get numbness and/or tingling in your feet while wearing cycling shoes, that suggests they don't fit. First thing that I would check would be to make sure you have enough width across the ball of the foot. Insufficient width there will cause you to crush some of the nerves (and you get numbness/tingling) between the metatarsals and can cause long-term neurological problems.

I have size 13A and 13AA feet. I have to find narrow, low-volume shoes, to get the length and enough space in the front for my toes, and then have the fastening system tighten enough across the instep to keep my toes away from the front of the shoes. I suspect you might have wide feet, and that getting shoes just fit for length may mean that you do not have enough width, and that is the cause of your numbness.

When SPD's first came out, a lot of people complained that the cleat was too small, and that their feet rocked laterally, and that that caused a "hot spot" on the bottom of the foot directly above the cleat, and caused numbness/tingling. Supposedly Shimano eventually introduced the SPD-R with it's larger pedaling platform specifically to address that complaint.

It seemed to me that this complaint was rider-specific: some riders complained bitterly and swore off SPDs and switched back to the large pedaling platforms of the Looks or the Times, and some riders never had a problem and thought SPDs worked just fine. It was never clear to me whether this was a rider problem or a shoe (fit) problem, but over the years it has faded away and you don't hear it much anymore. Now I don't hear of riders switching to SPDs and complaining of hot spots and numbness/tingling.