True Manufacturing Company Z5.4 - Manual (Page 48)

Z5.4 & Z5 Treadmill Owner’s Guide
48
Treadbelt Tension
Chapter Seven: Care and Maintenance
Turn both rear roller adjustment bolts counter-clockwise until
treadbelt just begins slipping when walking on it, then turn both
rear roller adjustment bolts clockwise in equal quarter turn
increments until treadbelt stops slipping.
Note: Be sure to run on treadbelt to ensure that the treadbelt does
not slip while under load.