My plane has always had a little vibration around 22 to 24 knots. This has been true with several sets of tires, from Van's cheapies to Michelin to my current favorite, retreads from Desser. I've never worried too much about it, since that speed is a bit faster than typical taxi speeds, and during takeoff and landing, one passes through those speeds fairly quickly. However, after the last annual, during which I rotated the tires inside to out, the vibration showed up a fair bit more noticeable. In fact, it was quite noticeable right after landing as well, probably picking up the 2x excitation speed of 46 knots.
I built the balancer shown in the pictures below. I used a couple very small ball bearings for minimal friction, a precision 1.25" shaft, and a couple collars to clamp the wheel bearings snugly. I put the first wheel on, and it lazily found a preferred position. It didn't seem like a lot of imbalance, but it took a fairly sizable piece of lead (don't tell California) to bring it to balance (the small wheel diameter). The other wheel took a piece perhaps 1/4 the size of the one in the picture. I used some 3m double sticky pads to attach the lead.
I went out flying, with some taxiing up to 28 knots, and no vibration at all! On landing, I held the speed up down the runway, exploring the whole range of speeds, and not the slightest sign of any vibration.
What was quite a surprise is how little imbalance there seemed to be when I first put the wheel on the balancer. I really would not have thought it to be a problem, until I saw how much lead it took.
The small bearings, without seals, are key, as anything larger probably would have had too much friction.