Vr= 1.1 or 1,05 Vmu [minimum unstick speed--all engines]
or at least 1.05 Vmca [min control speed in the air]
0r 1.10 Vs [stall speed power off] or a spped that allows V2 to be at least 1.1 Vmca or 1.2 Vms1 [min stall speed at specific Take off flap setting] ----
----V1 controls the accelerate stop distance
Vx = on a jet [L/D] max
Vb as said above max gust intensity
V1 Vr or V2 may be different than the minima above due to specific performance considerations such a V2 over speed schedules, V1 wet, V1max, Vr=V1 etc...