See below for the selection of Vr
Vr must be equal to or greater than V1.
· Vr must be equal to or greater than VMCG.
· Vr must be at least 5% greater than VMCA. This buffer is to assure that if an engine failed as the aircraft
was rotating to takeoff nose attitude, the rudder and ailerons alone is sufficient to enable the flight crew to
hold the aircraft straight.
· Vr must be compatible with reaching V2 as the aircraft reaches 35 ft above the takeoff surface with 1
engine inoperative. Vr infact guarantees that the aircraft reaches 35 ft/V2 in the minimum takeoff distance,
and no later than the end of the TODA.
Correct Vr will ensure that even if the aircraft is rotated at the maximum rate the aircraft will actually lift
off the ground (VLOF) without the tail striking the runway. Correct Vr will ensure VLOF is at least 1.1
VMU all engines and 1.05 VMU 1 engine inoperative
· Some very long aircraft have a Vr which is artificially high because they are prone to tailstrike during
rotation. This is often referred to as “geometry limited Vr”. It is a higher speed than would otherwise be
required to meet the other criteria listed above.
· Rotating at correct Vr will allow optimum acceleration to V2.
taken from this document
http://www.aviationshop.com.au/avfac...inst/inst2.PDF
And it contains all the speeds and what effects them that you could ever need.