FastJake

Straight pull spokes seem like a good idea, eliminating the bend where most spokes seem to break. So why aren't they more common? Are the hubs more expensive? Sure, they will spin when trying to tension, but with bladed spokes it's a non-issue since the blade is the perfect thing to grab onto.

I was surprised to not find much discussion of this despite some searching.

Bill Kapaun

If wheels were properly tensioned when built, it'd really not be an issue.
Just looking at the hubs, which requires more machining from the raw cast state? Access, such as machining the "socket" the spoke sits in for a SP spoke etc.
Bladed spokes are in a different category. Namely much higher priced bikes/wheels.
"Round" SP spokes may not work on the automatic wheel building machines because of potential "spinning". Let's face it. Most new wheels are machine built. You're also not going to put bladed spokes on xmart type bikes.

_ForceD_

According to DT Swiss, they feel that J-bend and straight spoke are close to equal WRT to strength. It's shortcuts in the wheel building process, and mismatched interface that causes J-bends to break more. The following cut-n-pasted from the article linked below.
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Is there any significant loss in strength between a J-bend or a straight-pull spoke in real life?

J-bends spokes tend to suffer more breakage issues due to poor build quality and low spoke tension. Also, some hubs have spokes holes too large, which causes poor fit of the elbow. Most of the time you can chalk up premature J-bend spoke breakage to corners being cut in the wheel-building process. For example: it's always surprising to me to see a shop build wheels without the use of a spoke tensiometer. To me, that's like trying to build a house without a tape measure! I can't speak for other brands of spokes, but I can say that our J-bend and our straight-pull spokes are very close in quality and strength. Going forward, DT Swiss will be offering more versions of straight-pull spokes due to numerous requests as field replacements on other brands of wheels/build, or for new wheel builds on DT hubs.

https://www.pinkbike.com/news/to-the...okes-2013.html

Dan

FastJake

Not working in automatic wheel building machines makes sense. Obviously I don't expect to see them on x-mart bikes, but they still seem more rare than they could be.

I read that article, but unfortunately it sounds like they interviewed a salesperson instead of an engineer. The responses include factual errors such as "The forging process allows the metal to be compressed into a denser package..." and dumbed-down explanations. Of course their j-bend and straight pull spokes will have similar ultimate tensile strength, if they're made with the same material and same manufacturing processes. But that doesn't predict the fatigue life, which also depends on the design.

I will agree that most spoke failures can be prevented through competent wheel building, but a weak point is still a weak point. And that's where I've seen almost every spoke break (the other location is the threads.)

ljsense

Some of it is probably tradition and aesthetics. Decades of experience have trained a lot of cyclists into what a hub "should" look like. And that design may be easier to create or assemble into a wheel.

When you have a rim with 28, 32 or 36 spokes, there is probably no benefit to using straight-pull spokes.

I've ridden lots of wheels, though, with low spoke counts with j-bends, and they've worked well.

It's often easier to replace a j-bend spoke when one breaks. You don't have to partially disassemble the hub, which is necessary with some straight-pull designs.

FastJake

Good point. I never considered whether a 32-36 spoke wheel could even work with straight pull. Maybe the hub would have to be huge?

I also wasn't aware of the potential issues replacing straight pull spokes.

davidad

A DT 2mm spoke has a tensile strength of at least 280kG. In Gerd Schraner's bool he shows a 2mm double butted spoke that broke at 285 kg after stretching about 5mm. It broke in the butted section.
Much of bike science is based on tradition amassed over 2 hundred years.
Ultimately if it isn't broke don't fix it.

cpach

Straight pull spokes are really nice, in my opinion, for higher end factory built wheels because they eliminate the need to correct the spoke line against the hub flange and are less in need of stress relieving.

I don't think there's much, if any, advantage to straight pull in a well built handbuilt wheel and straight pull has more restrictions on build parameters and the spokes are less common as replacement parts, though neither is a big deal. The hubs are usually a touch more expensive as well.

August West

Straight pull versus flanged hubs

mrrabbit 

...and they completely ignored the importance of stress relieving.

My Tomasinni is using DT Swiss 15g spokes from 1978 that are now on their 4th wheels set - 100,000 plus miles on these spokes so far. And of course, they are J-Bends.

=8-)

FastJake

Thanks all for the insightful comments! This clears up some mystery for me.