There's no formula for choosing the right traveler . . .
But there is an organized method for selection, based on knowledge of traveler characteristics of yarn to be processed and experience in traveler application. Traveler selection has no hard and fast rules, but the choice of traveler is very important in producing good yarn number, a certain specific weight of traveler is required. But that weight is distributed on travelers of many shapes and styles designed to correspond with the type of ring used and the yarn to be processed.
What the traveler does - What influences selection . . .
The basic functions of the ring traveler are to lay yarn on the bobbin under the proper tension, control the balloon of the yarns, work together with their rotating bobbin and front roller delivery to insert twist into the yarn, and to act as a differential for the surface speed of the yarn as it varies during formation of the package.
Many variations influence proper traveler selection - the spinning and twisting equipment used, different rings, different yarns and fibers, count, twist, yarn appearance required and production speeds. Only experience and experimentation - aided by a stroboscope with a good bright light to observe some of the points to be considered - will lead to the most suitable traveler.