My 422 smallblock build
Why would wheel diameter have anything to do with hydraulic or solid? I totally agree that the bigger the wheel the better but why would it be less desirable on a solid application. The wheel is going to make the same amount of revolutions per camshaft rotation regardless if it’s hydraulic or solid.
Actually there are a couple of reasons. As I've posted before, the de facto wheel diameter is .750 because that is all you can fit in an .842 bore.
Chrysler's use a bigger diameter core than Chevrolet. That means for the same lift, the Chrylser will have a higher wheel speed. Wheel speed can be critical as RPM goes up.
If the lobe is ground for a specific wheel diameter, changes either larger or smaller changes the cam timing.
A solid roller wheel changes speed with every lash cycle. It slows down as it gains lash and actually skids to gain speed as it wheel gets on the lash ramp. A hydraulic roller wheel never gets lash so the wheel does not speed up and slow down.
The smaller the wheel, the smaller the shaft axle where the needles ride. Again, it's a speed thing.
As I've said, there are many factors that go along with wheel speed like cam materiel, lobe design, the materiel of the wheel and a ton of other things like pushrod stiffness (or lack thereof), lifter to bore clearance, lash and lash ramp design and more I'm not thinking of that change the resonance frequency of not only the lifter but the entire valve train. Some call it the harmonic wave length.
At any rate, if you run the lifter into a frequency the wheel on the lifter will mimic a tuning fork. It will literally vibrate. This not only fails the wheel and axle but it will break the rivets holding the link bars on the lifter, the adjuster lock nuts will back off no matter how much torque you give them and many other anomalies that break parts that shouldn't break and it's not the parts fault, it the lifter in a reasonance frequency.