I have been trying to understand why after Flexing or Assuming from a Runway Analysis table and you get to the top of the table, in this case the max temp. that you can assume, (in my company's case the 767-300ER tables max flex temp is about 62 degrees), if the weight disparity is still too great say over five tons then you have to refer to the volume one to get the speeds for your actual weight, my question is why do you use the actual OAT for V speed corrections and not the temperature you have just Assumed at, i am aware that the speeds on the Vol. 1 are based on a balanced field length but whats this got to do with anything?

Anyone please, shed some light on this, thanks!

Just my guess:
Since actual temperature hasn't changed, hence density hasn't changed you get airborne at the same speed, so Vr for actual temp is used.

Since with an assumed temp you always have the option to use max (fixed derated) thrust you need to have speeds which correspond to the higher thrust, so again using actual temp for V1 (which has a relation with Vmcg, which relates to actual thrust, which relates to actual temp).

V2 relates to Vmca and Vs, so same story.

Standing by to be corrected.