Here’s a really quick breakdown of how different wheel’s tensions work.
All spinning wheels, as simple machines, require tension within the system. The system can be divided into: Double Drive, Scotch tension, and Irish Brake.
Double drive tension is the only all positive tension system, as the drive band and the bobbin are attached with the same band, they are subject to a similar amount of tension, and there is no band attempting to slow one part of the flyer system down. Both Scotch and Irish tension systems add negative tensions, attempt to slow something down.
However with a double drive the groves that the band rests on are different, the flyer has a V shaped grove which allowing for the maximum amount of friction and catch to drive the system. In contrast, the bobbin has a U shaped grove allowing for a larger amount of slippage, which allows you the spinner to accumulate twist without the yarn being yanked out of your hands.
Double drive has its advantage in that it allows for control without having to change constantly or worry about tension independent of the drive band to be accidently adjusted. It is great for intermediate to advanced spinners, but often harder for beginners as there work is often less regular.
Scotch tension works by slowing the bobbin down, allowing the flyer, driven by the drive band, to “wrap” the slowed bobbin with yarn. It applies a negative tension to the bobbin.
Scotch tension is the considered to be the best tension for beginners as it can more readily adjust to the varying problems and difficulties. When learning to spin treadle work doesn’t always match hand work, depending on the contrast, a stronger draw by applying more tension might be needed, or less draw to match slower treadling. The ability to constantly adjust the tension for up take allows for more flexibility for beginners.
Irish Brake is the opposite of Scotch, the drive band is attached to the bobbin, so the system is “bobbin driven.” At the front of the flyer attached to the mother of all is the Irish brake a band of leather that slows the flyer so as to change both the rate of the uptake as well as the amount of twist. For thick yarns and jumbo flyers, a bobbin lead wheel can have more yarn and weight added, as the bobbin is doing the majority of the work, with this system a full bobbin will have plenty of pull.