Many thanks for all the replies.
MU3001A, perfect, just the answer I needed! I won't have easy access to the performance manuals until two hours before the flight, and being new to operating at these altitudes, this issue was causing me some sleeplessness!
Genghis, in the manuals that I do have easy access to, the manufacturers state tyre limiting speed as groundspeed. After all, TAS only equals GS in zero wind conditions?? This a/c allows a maximum tailwind for take off of 10 kts, so that would have to be added to TAS to confirm GS was under max V tire.
The perf manual is still on the aircraft, its just that I'm nowhere near the aircraft!
Rainboe, sounds like a useful rule of thumb, and comparing it to MU3001A's calculations, fairly accurate!