Spokes for LB Build?!

[Luften]

It's in the specs here (see the third pic):
https://www.starbike.com/en/sapim-super-cx/

[pdlpsher1]

How can cx-super have a strength of 1980 N/mm2? Sure about that?

That's one heck of a leap in steel strength. I'd be skeptical of such claims.

This number is deceiving. It's expressed in force/area. Because the CX-Super is so thin a high number doesn't mean the spoke is strong. You have to multiply this number by the cross-section area to get the tensile stregth. A thicker spoke will always have a higher tensile strength (see the attached chart).

The reason why a thinner spoke shows a higher force/area is due to strain hardening. Then metal is stretch it becomes stronger until it breaks. A thinner spoke wins on this metric because Sapim is using force/area rather than just force.

Ultimate strength matters little in spoke selection. No spoke will break under tension due to lack of ultimate strength. Spokes break due to fatigue. The way you reduce fatigue is to limit the range of spoke tension changes. Butted spokes are better in this regard. And between two different butted spokes having two different cross-sections, the one with the greater cross-section will reduce the spoke tension change. There's a separate video on this which I will attempt to find it.

[pdlpsher1]

This videos highlights the importance of a high spoke tension on reduction of the dynamic tension changes. The lower the dynamic tension changes the longer the fatigue life of the spoke. With two butted spokes having the same spoke tension, the one with the greater cross-section area will be stiffer and thus reduce the dynamic tension changes. In conclusion, the CX-Ray will be better than the CX-Super in terms of wheel stiffness, power transfer, and fatigue life. Don't be misled by the marketing ploy that the CX-Super having a higher tensile strength for the middle section expressed in force/area. There's no free lunch when it comes to physics.

https://www.youtube.com/watch?v=B-pgyVFFQ5A

[Luften]

Interesting, thanks. I'm off the CX-Supers... I'll do CX-Ray or maybe the CX-Ray/Sprint combo (actually for only about 10g extra it seems to make a lot of sense).

What's your take on carbon spokes?

[pdlpsher1]

You're welcome. I'm not a big fan of mixing spoke types. Let's say you have two choices, 1) 28 hole CX-Ray only, and 2) 24 hole CX-Ray on NDS and CX-Sprint on DS. Option 1 will be far stiffer and stronger. BUT you want the X-Flow, hence the problem of having only a 20 or 24 hole option. With 24H laced in a 1:1 pattern, there's a chance that the wheel will be lacking in stiffness as compared to your WTO 21H laced in a 2:1 pattern regardless of what spokes you use. If you don't mind using the Extralite 2:1 hub I'd go with CX-Ray only 24H 2:1 lacing. By the way the WTO uses a spoke that is slightly heavier than the CX-Ray. If you insist on Carbon-Ti hubs then I'd advise 24 CX-Sprint to match the stiffness of your WTOs. For the front wheel 20H CX-Ray is sufficient.

Personally I'd not use carbon spokes. The disadvantages outweighs the advantages.

[Luften]

What are the disadvantages of carbon? Are they on-the-bike specific issues, or service/maintenance?

I just spoke with a wheelbuilder and I think I'm less keen on the extralite... I was told they require very regular maintenance (cleaning and regreasing multiple times a season), and only 2 pawl and 30ish tooth rachet. Apparently the disc brake ones are even worse to maintain as they freehub body and ratchet ring require replacing every season! But as this is a rim brake build it's the traditional system that doesn't wear out so easily thankfully. Do you have a view on the extralite hubs in general? Maybe with the XD15 bearings they'd be better? I don't actually ride in the rain (at least never intentionally).

Also I got some good feedback on the CX-Sprint/Ray combo. What's the downside to mixing these spokes?

[pdlpsher1]

One thing that comes to mind about carbon spoke is impact resistance, or lack thereof. When I ride I get hit by rocks a lot. I have dings on my rims, crank arms shoes, and forks. But my steel spokes have never been damaged by a rock. Steel spokes are elastic. Carbon spokes have great tensile strength but very brittle. I don't want to start a debate on steel vs. carbon spokes. There are people with carbon spokes and have no issues. But like many things in life some choices come with compromises. To me personally the negatives outweighs the positives. YMMV.

As for the CX-Sprint, I have never gone for a heavier spoke because if I want stiffness I just simply increase the spoke count while using a lighter spoke. Increasing the spoke count is the most effective way to increase the performance without adding a ton of weight. Using a heavier spoke to create stiffness is just not as ideal as adding four additional spokes.

I'd agree with your choice to avoid Extralite. Again, I don't want to start another debate on lightweight hubs. In general the hub is NOT the place you want to save weight. I'll take a heavier and more durable hub over a lighter and less durable hub on any day. The place to save weight is on the rim and nipples.

[NovemberDave]

Dave is using the ultimate yield strength which is totally irrelevant.

No it's not. The discussion here is of stiffness. No one is more vocal than me about why spokes break, which is fatigue, but that's not the discussion here. The discussion here is wheel stiffness. The information given in the linked post is absolutely relevant to this discussion.

[pdlpsher1]

Aren’t you and I saying the same thing? The 1900 N/mm2 number given by Sapim has nothing to do with stiffness. Dumb marketing ploy by Sapim to make the CX-Super look like a better spoke.


Sent from my iPhone using Tapatalk

[rides4beer]

I went with option 3 on my AR56s and they've been great. I'm 83kg and put down good power and have not had any issues with them riding/racing hard over the last six months.

[NovemberDave]

Aren’t you and I saying the same thing?

I don't know if we are or not. The question was "is X spoke stiff enough," which is a function of cross-sectional area for any given material, which is what the linked post talks about. You talked about spoke breakage through fatigue, which was out of the topic to that point. I agree that the ultimate yield strength of a spoke matters little to none in a wheel build. I just this morning got an email from a customer - "the number one thing is these spokes need to be strong!," which is a conversation I can't even have any more.

[pdlpsher1]

This is what I said...see the attached. I know fatigue is irrelevent in the discussion and said what's relevant is the stiffness of the spoke. I advised against the CX-Super because it has too little cross-section to create a stiff wheel for the OP's weight and power output.

Spokes don’t fail in yield. They fail under fatigue. What’s relevant for our discussion is the stiffness of the spoke. The greater the cross section, the greater the stiffness. The greater the stiffness, the smaller the range of spoke tension changes while riding with everything being equal. The smaller the range of spoke tension while riding the more durable the spoke, nipple, and rim will be.

[NovemberDave]

Sure. But your initial statement in the post I quoted was that the blog that the OP had found was irrelevant. It has all of this info in it. Fully relevant.