Twist and… OUCH!

January 28, 2024 1 Comment

What about spoke twist?
As a nipple is tightened, its spoke wants to wind up. The spoke head anchors one end so its length can twist into a spiral.

Problems
Windup can cause spokes to break, usually at their weakest point—the first thread or a butting transition. A twisted spoke can later unwind during riding, causing untrueness and making pinging noises.

Aero spokes have bigger problems:

• Twisting cancels their aerodynamic advantage.
• A twisted spoke is unsightly, and casts a shadow on a wheel’s integrity.
• Aero spoke profiles are less resistant to twist forces than round shapes.
• Direct pull spokes require precise aiming as their heads do not automatically sit correctly.

Hidden trouble
Wait, there's more, tension measurement—even a small degree of twist can fool a tensiometer. To a tensiometer, a twisted aero spoke appears thicker.

Either of those mistakes can create giant errors. Windup (spiral deformation) is as bad as rotation (incorrect aim). Either one messes up tension measurement, and the error can be sprinkled unevenly throughout a wheel. How often does this happen? A lot!

Prevention

• When lacing direct pull hubs, carefully aim aero spokes. Be sure they are set in the hub at the exact correct rotation. They’re very difficult to straighten once tight and may unwind later during riding.
• When tensioning, aero spokes must be held from twisting. Even small amounts will impact tension measurement. This applies to both j-bend and direct pull heads.
• When truing a wheel, notice spoke rotation and windup. Be careful measuring tension on spokes that are not perfectly aligned. Twist is easily seen on aero spokes. For round spokes, you can draw a line down the wire or attach a tiny tape flag so twist is detected. Some builders hold the spoke being tightened so rotation can be felt.
• Use a Wheel Fanatyk tensiometer. Jobst design anticipates this issue by removing spoke thickness (actual and perceived) from the process.

Here are numbers to show the magnitude of trouble we face. These measurements were taken on a CX-Ray spoke at 100kgf. Readings should all be 100kgf. Differences are owed to gauge accuracy and twisting induced error.
These represent an afternoon of casual measurements in which the test spoke was rotated and wound up in order to see the effects on the readings of two tensiometers. Ugly.

Note: I chose these tensiometers because they are highly reputed. Wheel Fanatyk is the only design which nearly overlooks spoke thickness and P&K Lie is exceptionally accurate over a wide range of spoke types.

Bottom line, twisted spokes are BAD (except on lowriders), but you don't need to be fooled!

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