I received an interesting question from a European tape user with whom I frequently correspond:
“Is there any speed variation when playing a tape with different hubs on the supply reel and take-up reel?”
And I replied:
You raise an interesting question. The easiest answer to this is simple:
There is a risk of speed variations throughout the reel if the tape tension varies throughout the reel.
followed by the corollary:
This effect is made worse if the condition of the capstan / pinch-roller system is degraded.
Some capstan / pinch-roller / constant-torque systems handle this better than others.