I don't have any way to measure tension in the cable. I set mine so that the 2->1 shift pulls the cable as far out as it will go just as the #1 shift position clicks into place. This takes maybe 3~4 seconds and I don't have to guess/ride the bike/adjust/ride the bike to get it where it works.
Here's what SRAM sez:
*Place the shifter in gear position "3". Move the crank to check that the gear is engaged.
*To make the adjustment, the cable must be taut in third gear to be able to transfer a shift movement directly to the hub.
*Push locating sleeve onto the small pull rod until the control cable is taut. Make sure that you don't pull the indicator chain out of the return pulley.
*Placed shifter in gear position "1" while moving the crank.
*Setting too loose: In gear position "1" the tension chain can be pulled out of the return pulley by hand.
*Setting too tight: It is difficult to place the shift lever in gear position "1".
*If required, readjust the shift mechanism (in third gear).
Fun fact: The SRAM T3 is the most popular IGH in the world.
Last edited by tcs; 02-14-11 at 07:13 AM.