Originally Posted by
TiHabanero
I know this will light off a firestorm, and for that I apologize, however I see all over the forums the statement that double butted spokes are more durable and less likely to break than straight gauge spokes, but have not seen any data supporting this claim.
What I do have is personal real world experience with straight gauge spokes. All wheels I built for myself have been straight gauge 2.0 Champions, and I have yet to experience broken spokes.
Claiming tensile strength is superior for DB spokes is one thing, but in a wheel tensile strength is not being tested. The movement of a spoke in the hub hole and at the nipple is where I see them break, never elsewhere.
I am looking for conclusive proof in a study format that backs up what I see people putting out there. Not interested in tensile strength or what Jobst has to say about it. I am interested in the flex of the spoke when under load and the fatigue failure rate between DB and straight gauge spokes.
Is there any such studies? Evidence?
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.