Building with Sapim CX-Ray spokes

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Samuel D
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Building with Sapim CX-Ray spokes

Postby Samuel D » 17 Mar 2019, 10:02am

I can muddle along but wouldn’t mind a few pointers from those with more experience of aero spokes.

First, do these lightweight spokes stretch appreciably farther than regular ones? I ask because I’ve ended up with left spokes ~2 mm shorter than the calculated value for a rear wheel (by relying on ERD reports on the web plus spoke length that erred in the unfortunate direction because of the 2 mm increments available). The right spokes are per the calculation. Brass nipples. Risky enough that I should order the right spoke lengths (2 mm longer) for the left side before starting the job?

Second, the wind-up and stick-slip is so severe with these spokes that it becomes a problem to adjust nipples by no less than a quarter-turn as I normally do per Brandt. Turning the nipple farther and then coming back to unwind the spoke sometimes requires a one-eighth turn interval to accommodate the slip-stick. Is forcibly holding the top of the flat section to prevent wind-up acceptable or does that risk wringing its neck off?

Third, how do you stress relieve these? Doing it the Brandt way bends the spokes in the direction they don’t like even if you can find gloves thick enough to protect your hands from the sharp edges.

Thanks.

Brucey
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Joined: 4 Jan 2012, 6:25pm

Re: Building with Sapim CX-Ray spokes

Postby Brucey » 17 Mar 2019, 10:23am

NDS spokes in a (dished) derailleur gear wheel won't stretch appreciably, simply because they don't have much tension in them. Realistically if you get a lot more than 0.5mm stretch then the spoke must be much closer to yield than you might like it to be. You often get more movement than this by virtue of the spoke elbow settling in the hub anyway.

Given that these are NDS spokes without a lot of tension in them, one of the usual objections to having spokes that don't come up to the slot in the nipple is less of a concern, i.e. that the nipple might fail. So if you can find long nipples that also have a long thread in them, this might be a 'get out of jail free' card.

Re stress-relief, I'd suggest that you squeeze the spoke crossings towards one another, i.e. by using a movement that is paralell to the axle. This is what I do normally, and as you note it isn't practical to use some other techniques with aero spokes anyway. If you do manage to stress relieve aero spokes as Brandt suggests then they are often permanently deformed as a result.

You can buy a slotted plastic tool for holding aero spokes. It is easy enough to make your own, too. This usually works OK during a build but if the nipples have corroded and/or you have used threadlock, you can twist the spokes up (i.e. deform them permanently) before the nipples turn.

BTW what rims are you building with?

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

S2L
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Joined: 20 Feb 2019, 4:47pm

Re: Building with Sapim CX-Ray spokes

Postby S2L » 17 Mar 2019, 10:29am

I'v never made any special length correction for CX-Ray... I treat them as the spoke they come from, which is a Laser.
Differences in stretch are minimal anyway, maybe enough to round up or round down the millimeter, but certainly not enough to change the length.

I stress relieve by pressing on the rim... CX Ray don't really need much stress relieving as you build them with a slotted guide, so they shouldn't have any wind up.

I don't recommend the Sapim slotted "ring", as it's too short. The DT Swiss is much better, or build your own by sawing into a piece of wood

Samuel D
Posts: 2875
Joined: 8 Mar 2015, 11:05pm
Location: Paris

Re: Building with Sapim CX-Ray spokes

Postby Samuel D » 17 Mar 2019, 12:19pm

Brucey wrote:Re stress-relief, I'd suggest that you squeeze the spoke crossings towards one another, i.e. by using a movement that is paralell to the axle.

I’ll try that.

Brucey wrote:BTW what rims are you building with?

I already built the front with a 28-hole H PLUS SON Archetype that I measured the ERD of as reported here. The rear is a 32-hole Archetype that I have yet to receive. Maybe its ERD will be appreciably different but I doubt it. I suspect the differing ERDs reported online are mostly down to differences in measurement, usually bad! I measured the front rim accurately by dropping a nipple into a hole (in fact three holes to see if there were differences; there weren’t) and measuring the distance from the outer diameter of the rim to the top of the nipple. The result was 595 mm.

Hubs are DT Swiss 240S 11-speed road 100 mm / 142 mm Centre Lock Disc Brake with 12 mm through-axles … another nuisance because I had to get overpriced plastic widgets to do anything with them. The hub flanges were approximately as specified by DT Swiss in its online calculator (DT Swiss is no Shimano when it comes to documentation and I couldn’t find flange geometry specs anywhere on its website). I built the front wheel cross-2 with 282 mm and 284 mm spokes, 2 mm less than calculated. The spokes are within a whisker of the bottom of the nipple slots.

I have 288 mm spokes for the rear versus the calculated 288 mm and 290 mm for a cross-3 build. Nipples are 12 mm Sapim Polyax.

S2L wrote:I stress relieve by pressing on the rim... CX Ray don't really need much stress relieving as you build them with a slotted guide, so they shouldn't have any wind up.

I built the front wheel without holding the spokes by over-tightening and then undoing each spoke to unwind it. At least with bladed spokes it’s easy to gauge wind-up precisely.

However, by stress-relief I meant the Brandt definition of removing residual stresses in the elbow. Would even my body-weight on this stiff rim be sufficient to bring the elbow to yield? Seems unlikely and uncontrolled but I haven’t tried.

S2L wrote:I don't recommend the Sapim slotted "ring", as it's too short. The DT Swiss is much better, or build your own by sawing into a piece of wood

Thanks.

Brucey
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Joined: 4 Jan 2012, 6:25pm

Re: Building with Sapim CX-Ray spokes

Postby Brucey » 17 Mar 2019, 2:31pm

Archetypes I have built with in recent years have been 595mm, on the nose. There are multiple online reports of wheelbuilders measuring 595mm too.

The 593mm figure was correct for the first version of the archetype, which had a thinner spoke bed, and hasn't been current for about six years. There are enough folk who don't update their databases (or care if their spokes come 1mm short) that this figure still appears in places, even though it is quite wrong.

FWIW building with archetypes has one thing that might catch you out; moreso than with many other rims, the spoke tension is lost when the tyre is inflated. You should err on the side of high spoke tension when building the wheels; if the tension is near the minimum acceptable value when the wheel is built, it'll be too slack once the tyre is fitted and inflated.

cheers
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531colin
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Location: North Yorkshire

Re: Building with Sapim CX-Ray spokes

Postby 531colin » 17 Mar 2019, 6:35pm

Yeah, just cut a slot in a piece of Ali. to stop the spokes twisting.
Stress-relieving I now push the (third) crossing towards the mid-line of the bike. Like Brucey does, only I put the crossing on a big trolley wheel with a solid rubber "tyre" and push down on the wheel.....doesn't hurt my hands.

thelawnet
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Joined: 27 Aug 2010, 12:56am

Re: Building with Sapim CX-Ray spokes

Postby thelawnet » 17 Mar 2019, 9:15pm

is there any reason not to use aero spokes (are they significantly weaker, for example, though presumably you could use more of them)? The reason TO use them is apparently they might save you half a watt a 20mph? https://novemberbicycles.com/blogs/blog ... vs-cx-rays

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531colin
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Re: Building with Sapim CX-Ray spokes

Postby 531colin » 17 Mar 2019, 9:25pm

Its my recollection that Sapim publish something like "load/unload cycles to failure" and CX ray spokes are miles better than all the others.
The cynic in me (never, I hear you say) wonders if this is done without stress relief, and the superior performance of the CX rays is because the spoke doesn't flex at the elbow, but somewhere else.
Make that "used to publish".....can't find it on their site now

Brucey
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Re: Building with Sapim CX-Ray spokes

Postby Brucey » 17 Mar 2019, 9:55pm

I have had similar thoughts too. Sapim took the charts down a while ago; presumably they caused more confusion than they were worth, because folk were apt to predict the life of a wheel based on the idea that one wheel revolution was equivalent to one full stress cycle in the fatigue test (which it probably isn't of course). [edit despite this;
Image....]

Some discussion here

https://forums.roadbikereview.com/wheels-tires/sapim-cx-ray-spoke-life-calculation-330134.html

Suffice it to say that there are various issues when using these spokes, but a shorter fatigue life isn't a major one.

cheers
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Brucey
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Re: Building with Sapim CX-Ray spokes

Postby Brucey » 17 Mar 2019, 10:24pm

further to the above this page

http://flocycling.blogspot.com/2011/07/flo-cycling-component-series-part-3.html

attempts to compare fatigue data from 'a competitor spoke'

Image

with the sapim 'data' (which is nothing more than the same chart as I posted in the previous post) and they conclude that the Sapim spokes are 'ten times better' ….. :shock:

Well they might be. But unless the sapim test conditions are known, it is a meaningless comparison.

Take a look at this fatigue test data (not from spokes BTW)

Image

{NB this has a log scale horizontally; each large increment is x10 more cycles}.

You will also see that something which fatigues at ~10^5 cycles might be from a population that has an essentially infinite fatigue life when the stress amplitude is reduced to a (slightly) smaller value. So unless Sapim say what their stress amplitude is, their data is meaningless, and the 180kg stress reversal in the competitor spoke is way higher than you would reasonably expect to get in reality (probably chosen to make the test a bit shorter in fact) so I'd happily build with those 'competitor' spokes, based on that test data.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

thelawnet
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Joined: 27 Aug 2010, 12:56am

Re: Building with Sapim CX-Ray spokes

Postby thelawnet » 17 Mar 2019, 11:34pm



these people strike me as disingenuous at best

Here's another bit from them about the wonders of these spokes

http://flocycling.blogspot.com/2016/04/ ... rence.html

There's a lot of blather about experimental conditions, yaw, blah blah, but:

they try to avoid saying which spokes they compared with - cheap ones that don't seem like a reasonable comparator. (They also used their LEAST aero wheelset)

they don't explain how they derive their results, just baldly assert "it's 9s faster over 40km"

eventually they reveal that the wind speed tested was 30 mph

the 9s works out at 0.3% speed gain, which they claim is 'large'

If you are doing 30mph in a 25 mile time trial, ok maybe, but then they say it's 42s faster over an ironman course, also at 30mph. The problem being nobody has ever done 30mph on an Ironman course.

NickJP
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Joined: 24 Sep 2018, 7:11pm

Re: Building with Sapim CX-Ray spokes

Postby NickJP » 18 Mar 2019, 3:10am

I've built several pairs of wheels using CX-Ray spokes, including drive side rear, have never bothered to try to account for any possible additional stretch in the spokes, and I've not had any problem with that. To prevent spoke wind-up I hold the spokes just below the nipple with a slotted tool that came with a pair of Dura-Ace C24 wheels (you could make your own by hacksawing a slot in a piece of aluminium sheet), and I use DT Squorx nipples so that I can drive them from inside the rim.

For stress relieving I put on a rigger's leather glove, grab the spokes where they cross, and push them slightly apart. The glove's not absolutely necessary, but your fingers will get pretty sore without it.

Samuel D
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Location: Paris

Re: Building with Sapim CX-Ray spokes

Postby Samuel D » 18 Mar 2019, 9:22am

Brucey wrote:FWIW building with archetypes has one thing that might catch you out; moreso than with many other rims, the spoke tension is lost when the tyre is inflated. You should err on the side of high spoke tension when building the wheels; if the tension is near the minimum acceptable value when the wheel is built, it'll be too slack once the tyre is fitted and inflated.

Alright. I’ll give the spokes another 10 kg or so from the outset.

NickJP wrote:For stress relieving I put on a rigger's leather glove, grab the spokes where they cross, and push them slightly apart.

You mean pull one spoke with your fingers and push the other with your thumb at the last crossing, in-line with the hub’s axle? I am almost certain I wouldn’t have the strength to bring the elbow to yield with that technique, especially with stretchy spokes at anything less than fantastically high tension.

thelawnet wrote:is there any reason not to use aero spokes (are they significantly weaker, for example, though presumably you could use more of them)?

They’re a nuisance to build with as I’m finding out, but more importantly they’re many times more expensive than the conventionally swaged spokes I use for my own wheels. The spokes alone for this pair of wheels came to nearly 150 euros.

Judging from their low weight (lower even than Sapim Lasers with 1.5 mm mid-sections), the CX-Rays must stretch more than heavier spokes. Comments above suggest this isn’t enough to worry about when calculating spoke length, but it might be enough to keep the nipples from unscrewing in marginal builds.

thelawnet wrote:If you are doing 30mph in a 25 mile time trial, ok maybe, but then they say it's 42s faster over an ironman course, also at 30mph. The problem being nobody has ever done 30mph on an Ironman course.

I guess no-one has used the right spokes in an Ironman yet.

S2L
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Re: Building with Sapim CX-Ray spokes

Postby S2L » 18 Mar 2019, 5:07pm

thelawnet wrote: The problem being nobody has ever done 30mph on an Ironman course.


... and if he did, probably the margin on the second rider would be quite a lot more than 42 seconds anyway...

Brucey
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Re: Building with Sapim CX-Ray spokes

Postby Brucey » 20 Mar 2019, 7:52pm

how's it going, Samuel?
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