Building with Sapim CX-Ray spokes

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Samuel D
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Location: Paris

Re: Building with Sapim CX-Ray spokes

Postby Samuel D » 20 Mar 2019, 9:43pm

Brucey wrote:how's it going, Samuel?

Not too bad, thanks for asking.

I received the rear 32-hole Archetype rim and measured its ERD at 594.5 mm to the nearest half millimetre. This rim had an outer diameter of 634–635 mm (compared to 633 mm and perfectly round for the 28-hole front). But the drop to the spoke holes was greater, so the ERD was actually very fractionally less.

I decided to go ahead and build with the spokes I had. The left spokes ended up coming up to the base of the slot in the nipples, so I thought that would do fine. The right ones were perfect.

I built these wheels with as much tension as I dared (~130 kg drive-side rear, ~120 kg disc-side front), because they’re going under a very heavy, very strong rider. I would have opted for 36 spokes all around if the choice had been mine, even with Archetype rims and stretchy spokes. On the other hand, I’m glad I wasn’t building 36-spoke wheels with CX-Ray spokes, because even as it was there wasn’t much room to hold the spoke from twisting as I worked on the nipple.

I stress-relieved with your method upthread, squeezing as hard as I possibly could with one gloved hand. That felt like it did something and resulted in some more minor truing work.

Perhaps because of the high tension and marginal spoke length, I stripped the threads off one of the brass Sapim Polyax nipples on a rear-left spoke, somewhere near final tension. That was a first for me. Does that just happen from time to time? I ask because the shop had included one spare nipple that saved my bacon, and this wasn’t the first time a shop (different shops) has given me a nipple I didn’t pay for.

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Re: Building with Sapim CX-Ray spokes

Postby Brucey » 20 Mar 2019, 10:09pm

stripping nipple threads like that is pretty uncommon; less common (IME) than getting a defective nipple, I'd say. Since nipples are not expensive, they are easily lost, you can't be 100% sure that you haven't counted wrongly, and every now and then a nipple is faulty, it isn't unusual to get ' a wheelbuilder's dozen' as it were.

Sounds like you got lucky there with the lengths; 'flush with the slot bottom' is an acceptable spoke length IMV.


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

Re: Building with Sapim CX-Ray spokes

Postby Samuel D » 20 Mar 2019, 10:32pm

I see. Well, I was glad of that wheel-builder’s dozen this time.

The right spokes would have been a tad too long if the ERD had been 593 mm as I expected and not 594.5 mm.

Lesson learned again: do your own measurements! Especially if spokes are sold in 2 mm increments.

On another note, 11-speed disc-brake through-axle hubs are fairly ridiculous things. They’re immensely wide and still have no room for the flanges.

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Re: Building with Sapim CX-Ray spokes

Postby drossall » 21 Mar 2019, 10:42pm

Park do a bladed spoke holder if that would help?

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Re: Building with Sapim CX-Ray spokes

Postby Gattonero » 23 Mar 2019, 1:10pm

Samuel D wrote: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.


The "stretch" of spokes is somewhat a myth that comes from incorrect lacing and stress-relieve of the whole wheel, plus uneven spoke tension.
Never found any real difference from round to flat spokes, aside the ability to control the torsion of the spoke in its length.

If one has to order expensive spokes, it pays to keep a stash of used spokes (again, emptying the bucket of a LBS proves very useful over time) to try before committing to order £2/each spokes. Once the lacing and nipples size/head type are put into accounts, the spoke length will have no difference between round and flat.

The torsion is controlled by preventing it: tension the highest first (i.e. on the rear will be the Rh side, on a front disk brake wheel it will be the Lh side) to about 70% the final maximum value, then do the opposite side.

I always stress-relieve by pressing the whole wheel on the floor, then tapping each spoke cross with a rubber mallet. It works better for my style.
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since you have to sweat up the hills and coast down them.
Thus you remember them as they actually are...