Wheel vibration gives the flexibility required, but it also
has limitations which must still be resolved. In wheel vibration, the
transducer is incorporated into the spindle construction. Such an assembly
induces the problem of isolating the vibration from the spindle
bearings. If proper vibration isolation is not attained, undue bearing
loads and wear may be expected. This was recognized as a critical limitation,
and, consequently, major research effort has been directed toward
its solution. Research results, as yet unpublished, indicate that this
problem may shortly be overcome.