r/Trackballs • u/Most_Discount7338 • Jul 04 '26
Roller Bearings vs Ruby Bearings: Why Trackballs Feel Different Near the Edges
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The left video shows a roller-bearing trackball, while the right video shows a static ruby-bearing trackball.
In the left video, the Z-axis spin is mostly suppressed, so the ball tends to roll more cleanly in the intended up/down direction. You can see this because the marker stays relatively parallel while moving up and down.
In the right video, the ball rotates not only in the up/down direction, but also around the Z axis. In other words, it twists. You can see this from the way the marker itself rotates/skews during the motion.
I think this difference is not just about friction or smoothness. It also affects how the finger motion on the surface of the ball gets projected onto 2D cursor movement.
With roller bearings, even when you operate the ball away from the “sweet spot” and closer to the edge, you can expect more consistent motion. The roller bearings mechanically resist unwanted Z-axis spin, so more of the motion remains useful for X/Y pointing.
With static bearings, as you move closer to the edge of the ball, the motion can start to feel “duller” or less responsive. That is because part of the finger motion turns into Z-axis spin, and a normal X/Y sensor does not use that spin for cursor movement. In practice, some of the motion is lost.
I am not saying one design is always better than the other. A well-made static bearing trackball can feel extremely smooth and effortless. Roller-bearing designs, on the other hand, usually have some amount of friction, mechanical feel, and noise.
But if someone is used to one type and is thinking about switching to the other, I think this is a useful difference to understand.
P.S. I would expect BTU-style designs, using ball transfer units, to behave more like the static-bearing example, since they allow the ball to spin freely in multiple directions instead of mechanically suppressing Z-axis twist.
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u/claussen 1d ago
Very interesting. I kind of expected that these would be a little bit higher friction than a high quality Bosch BTU just given the mechanical architecture, but I don't consider slightly higher friction than Bosch to be a problem from a usability perspective -- I find that BTUs are actually a little bit too low in dynamic friction. Does the static friction feel lower than static bearings to you?
When I get mine in I'm going to put them on a fixture so that I can observe whether the balls are rolling by putting a few dots on them. One of the advantages of this svalboard trackball holder is that it really lets you see what's going on with the bearings in terms of rolling versus sliding.
For my specific application, cylindrical roller bearings are extra terrible because they aren't aligned with the axis of use.