Yarns of warp beams to knit on warp knitting machines need to be wound at equal tensions. The tension variations lead to produce valleys and ridges of warp yarns on the beam and hence different lengths of individual warp yarns. These length variations lead to loop length variations in warp knitted fabrics and may cause defects along the wales. This research aimed at investigating the warp length variations caused by tension variations and its effect on the quality of the fabrics knitted. Tension variations of individual warp yarns on warp beams for warp knitting were examined. 16% of warp yarns were outside the permissible tension range in practical environment. The length measurements of 1128 individual yarns of a warp beam show that 0-1.7% length variations exist among the yarns. The fabrics knitted at different tension values ranging from 4cN to 20cN show 6.6% increase in wale density. Although the fabric weight variation is below 5%, the microscopic view of the fabrics shows significant change in the size of loops and rupture of filaments. This has caused visual colour difference in the fabric.