Old 08-04-19, 12:42 PM
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Originally Posted by cyccommute View Post
Let’s start with tensile strength. The tensile strength being measured isn’t the wheel but the resistance of the spoke to breakage. Tensile strength measurements of the spoke gives you insight into how much it takes to fatigue the spoke to the point where it will break. Higher tensile strength (or resistance to breakage) will result in a strong, more durable wheel.

Pillar spokes is about the only place where I’ve seen actual measurements of tensile strength of various types of spokes. You have to look at multiple graphs to see what effect butting has on strength but it’s pretty clear when you compare them. For example a 2.0mm (14ga) spoke breaks at 270 kgf (kilograms force which is a really dumb unit). A 2.0/1.8/2.0mm breaks at 290 kgf (about) and a 2.2/1.8/2.0mm spoke breaks at about 330 kgf. They have a 2.3/1.8/2.0mm triple butted spoke that breaks at about 420 kgf. For comparison, their 2.3mm straight spoke breaks at about 360 kgf.

Their charts show pretty conclusively that butting the spokes increases their strength.
Originally Posted by cyccommute View Post
The ultimate tensile strength is a good indicator of fatigue life and elasticity. Fatigue life is difficult to measure and the modulus of elasticity can (and is) measured during the tensile strength test.
Does anybody care about the tensile strength of a spoke at breaking? It's the usual shuck and jive attempt to cover up erroneous pontifications. Modulus of elasticity, yield strength, and fatigue life are independent of breaking strength and are investigated, specified and published for structural metals and each is used to inform the design process. Your “breakage” force is only meaningful at catastrophic failure for determining safety factors.

Clue: Fatigue life, yield strength, and modulus of elasticity are all measured independently of ultimate tensile strength at breakage. Keep going down your rabbit hole and you’ll soon post something like “Tighten the nipple until the spoke breaks then back off x turns.” HAW!

Last edited by AnkleWork; 08-04-19 at 02:03 PM.
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