In reply to the question about my application...
The shock and durability requirement would be much less than an inline skate wheel. That still might seem like a lot, but the force is always glancing since the wheel is on a bearing. And in this case, the bearings might be in two rows, staggered (like in the link below, but much smaller). Also, these small wheels will not be used for pushing, so there will be no typical wear like on a skate wheel. Also, they will not be in contact with the ground during ordinary use, only when the front wheel dips into a pit or pothole. There is a radical example of applied force, like when jumping up onto a curb and landing in the middle of the frame, but I'm interested only a reasonably functional version.
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I'm sure Alexander Bont came up with the concept of staggered skate wheels before I did, but (with all due respect) the best application of staggered wheels is rough terrain skating, not downhill.
There are lots of off-road inline skates that are supposed to resemble skis, but with only two wheels (one in front and one in back), they are nothing like skis. They are like an all-or-nothing seesaw. In order to resemble skis (on dry land), skates must have center wheels like an ordinary inline skate. Only the front wheel size matters for traversing obstacles on rough terrain. Trailing wheels can be small if they are closely spaced. And if the center wheels are not used normally, a medium or large rear wheel is useful. If the center wheels are very small and homemade like what I'm talking about, they won't be useful for turning, so they should probably not normally contact the ground. So that while turning the center wheels do not contact the ground, having two staggered rows of bearing wheels might be too wide. The wider they are, the higher off the ground they must be. Also possible is a tank tread setup using something like a fan belt and only one row of bearings.
The objective is to keep terrain from getting in between the wheels so that the ride over rough terrain is smoother. With As little device resistance as possible.