What Is Drive Ratio?
The drive ratio is the number of times the flyer (or bobbin) rotates for each turn of the drive wheel. A ratio of 8:1 means the flyer spins 8 times for every complete turn of the big wheel.
Higher ratios add more twist per treadle, which is what you want for thin, strong yarn (like sock or lace weight). Lower ratios add less twist per treadle, ideal for thick, soft yarn (like bulky weight).
To calculate your ratio: measure the diameter of your drive wheel and divide by the diameter of the whorl (the pulley on the flyer). If your wheel is 22 inches and the whorl is 2.5 inches: 22 ÷ 2.5 = 8.8:1.
Understanding TPI (Twists Per Inch)
TPI (twists per inch) is the direct measure of how tightly your yarn is spun. More twists = stronger, harder yarn. Fewer twists = softer, loftier yarn.
General TPI guidelines: lace weight = 12–20+ TPI, fingering/sock = 8–14 TPI, sport/DK = 5–8 TPI, worsted = 3–6 TPI, bulky = 2–4 TPI.
TPI depends on both your wheel ratio and how fast you draft (pull the fiber out). A high ratio with slow drafting produces very high TPI (tightly spun). A high ratio with fast drafting produces moderate TPI. Our TPI Calculator factors in both ratio and draft speed.
Choosing the Right Whorl
Most spinning wheels come with 2–3 whorls of different sizes. Smaller whorls create higher ratios (more twist). Larger whorls create lower ratios (less twist).
For lace and fingering: use your smallest whorl (highest ratio, typically 10:1 to 15:1). For DK and worsted: use a medium whorl (6:1 to 10:1). For bulky: use your largest whorl (4:1 to 6:1).
If your wheel's ratio range doesn't cover the yarn weight you want, you may need an aftermarket whorl set. Many wheel manufacturers sell additional whorls.
Plying for Balanced Yarn
Plying is twisting two or more singles together in the opposite direction of spinning. The plying twist counteracts the spinning twist, creating balanced yarn that hangs straight without curling.
The rule of thumb for balanced 2-ply yarn: ply at roughly 60% of your singles TPI in the opposite direction. If you spin your singles at 10 TPI in a clockwise (Z-twist) direction, ply at about 6 TPI counterclockwise (S-twist).
For 3-ply yarn, use about 50% of the singles TPI. The additional plies provide more structural stability, so less plying twist is needed.
Our Plying Calculator handles the math and reminds you about ply direction.