This is a really tough nut.

After a couple of hours research, I have not been able to find a direct translation for taper tension.

The term means that the tension of the paper being wound onto a reel (not off: that's Bahnspannung) is controlled to prevent excessive pressure developing inside the roll.

This is done by controlling the Bahnzug (tension) as a function of roll diameter (taper) which in turn has an effect on the internal roll pressure (Wickelhärte).

Hope that's enough to point you in the right direction.