B.C.A.R. determine VR by one of four criteria:
1./ 1.05xVMCA
2./ 1.10x the minimum power off stalling speed VMS
3./ 1.1 or 1.05x the minimum unstick speed VMU
4./ A speed which allows the greater of 1.1 VMCA or 1.2 VMS1 to be achieved at the screen height of 35ft with one eng. inop.
The above from Perf.A notes.