The Basics of Spinning Wheel Drive Ratios
Spinning wheels are pulley systems. Changing ratios is basically the same principle as changing gears on a bicycle, except instead of sprockets and chains, you’ve got pulleys and drive bands.
Simply put, a ratio of 5:1 means that the drive wheel’s circumference is 5 times that of the circumference of the thing being driven (like the whorl). For every time that the drive wheel completes one rotation, the thing being driven (whether it’s flyer whorl, or bobbin) will rotate 5
times. So if you treadled such that the drive wheel completed 30 rotations (or revolutions) per minute, the flyer or bobbin would complete 5 times that many, or 150. Your 30 rpm at the drive wheel becomes 150 rpm at the flyer or bobbin.
If you want your flyer or bobbin to be going faster than that, in order to make more twist go into your yarn faster as you are spinning, without different ratios, your only option would be to increase the speed of the drive wheel, say by treadling faster on a treadle-powered wheel. Increasing your speed to where you are going 60 rpm at the drive wheel would then increase flyer or bobbin speed in a directly linear way, still at a ratio of 5:1 — so now you’re going 300 rpm at the flyer.
But, let’s say that you have another ratio available to you, of 7 to 1. In this case, the drive wheel’s circumference is 7 times that of the driven object. Simply changing from the 5:1 ratio to the 7:1 ratio, without changing the speed at which you’re treadling or turning the drive wheel, changes you from going 30 rpm at the drive wheel and 150 rpm at the driven end, to 30 rpm at the drive wheel and 210 rpm at the driven end.
So, an application of this principle: let’s say that I want to spin a really fine and high-twist yarn at a rate of, say, 1500 rpm at the flyer. To do this with a drive ratio of 5:1 on a treadle powered wheel where each treadle stroke represents a full rotation of the drive wheel, I’d have to treadle 300 times a minute!! Yowza! There’s no way that’s humanly possible. But at a ratio of 30:1, I’d only have to treadle 50 times a minute, to get 1500 rpm at the driven end. 😉
To sum up, different ratios allow you to get twist into your yarn at different rates while you are spinning, without changing the speed at which you treadle (or turn the drive wheel).
Going from a larger drive wheel circumference to a smaller driven item circumference, you get the biggest speed gains, and fastest flyer/bobbin rotation relative to treadling speed. Going from smallest drive wheel circumference to largest driven item circumference, you get the slowest flyer/bobbin speed relative to treadling speed. On most modern spinning wheels, this means if you have your drive band going around the largest groove on the drive wheel, and the smallest groove on your whorl, you’re going as fast as that wheel can go; if you’re going around the smallest groove on the drive wheel, and the largest groove on the whorl, you’re going as slow as that wheel can go.
Similar to bicycle gears, some ratios also can require more effort and force than others, just to get around — think of shifting to a low gear, for low-effort pedaling to get uphill, and then a higher gear, for greater speed on a flat stretch once you get going. The same effect is in play in pulley systems, but as implemented in spinning wheels, you typically need to be pushing the limits of your system in order to detect these effects to any great degree.