fooferdoggie 

We had about 8000 miles on the stock rear wheel on our e tandem it is a Shimano deore center lock disc hub 10 speed. 36 hole I don't remember what the rim is. When the pandemic was in full swing my wheel builder could only find 32 hole parts. So he used a dt swiss 350 32 hole e bike hub a velocity cliffhanger rim and sapim super strong spokes. The rim cracked after maybe 2000 miles. He replaced it under warranty and used washers on the spokes since the rim does not have them. Well maybe 400 miles later a spoke broke. He thinks because the slight bend the washers caused when he rebuilt it. So he will rebuild it with different nipples to fix that issue.
But I am debating on having the old wheel rebuilt with a cliffhanger rim or other ( I only found one other) and get the hub serviced too. Or when our tax returns get a white industries 40 hole hub and a 40 hole cliffhanger rim. Thats all we can find in rims. There is one other but it's for narrower tires. We use 1.5" tires. Plus Want to keep it tubeless too. But it would be around 600 for the real wheel verses at most 300 to have the old one re built. The tandem has a 148mm and uses a 12 mm through axle. So not sure if the white industries hub would work unless you can change the end carps to 148 from 145 like on the dt swiss?

Carbonfiberboy 

IME the problem is the "super strong spokes" combined with the box-section rim. Most folks don't know how a wheel actually works. You want 14-15 (2.0-1.8) double butted spokes, no matter the load. Steel is really strong. What wheels need is stretchy spokes to survive. Too stiff a spoke causes fatigue both in the spoke and in the rim. We run CX-Ray spokes on our tandem wheels, but those spokes a bit expensive.

The rims are also too flexible, which increases the varied load on the spokes. You want a stiffer rim. In the Velocity line, how about the Aileron or Chukker? Those are both available in 36H, as is the Cliffhanger, BTW. The Aileron is also quite a bit lighter. It's not weight that makes a strong rim, it's geometry.
https://www.velocityusa.com/product/rims#models-tab

Velocity is a US company. They have dealers, but I think you can also order from the factory. I don't think there's a better choice for tandem rims now.

And maybe a different wheel builder. Wheels that fail are not a good sign. Ask around.

fooferdoggie 

this is the spokes he used the first time https://www.sapim.be/spokes/butted/strong they are made just for heavy loads. but it seems that may be too much for the cliffhanger rim? the problem wast the bike has a disc brake on back and a rim brake as a backup so the cliffhanger what about the only choice. so when he rebuilt the wheel with washes he used the https://www.sapim.be/spokes/butted/force but the washers caused a slight angle at the nipple as seen I the pic. He has nipples that will prevent this now. he is fixing it for free but I am willing to spend more to make it well. the cliffhangerr was the only rim that did rim brakes and was tubeless ready and heavy duty.
if you go to velocity they recommend 40 hole but also the cliffhanger tire size starts at 45 where we are running 38's if we went wit the Aileron we would have to ditch the rim brake. I would pay for the best spokes. we wanted to go with 36 or 40 but the in 2021 where was nothing available.
thats why I went to this wheel builder his very highly recommended and all our other wheels are great. but I am fin buying another rim and high end spokes if it will make the wheel last. going to 40 hole would cost over 600.00 for the rear wheel.

ahultin

Running 38's I would advise against the aileron unless you are a lightweight team. We have had too many failures on the aileron. Velocity has warrantied them each time but blames it on the wide tires (started at 45's, most recent sidewall failure was 35's) and team weight 350-400 (several different stokers )
Our 650b set was finally replaced by velocity with the cliffhanger. We have had no issues with those in thousands of miles( 32h build, 145 white mi6, dt Swiss alpine III)

fooferdoggie 

we are 350 but the bike is maybe 70 or so pounds without any groceries. it seems the spokes he used were too much for the cliffhangers. the X-ray spokes may be the way to go I don't mind pay the extra for them if it all holds up. wish it was not so expensive going to 40 but only the white industries hub comes in 40.

Thebucket71

Why not consider the velocity atlas?I believe it's their only rim that comes with eyelets for the nipples.

IPassGas

A break at the nipple suggests that the angle is a problem, but it could be one bad spoke. You might fix it and go until more breakage occurs. If more break at nipple, DT Swiss and Sapim make conical spherical nipples that are better for greater angles at rim. 32h rims are not good for a heavy tandem plus (I assume without experience) the extra torque from motors. Only 16 spokes are carrying the load on a dished wheel. You might also consider another wheel builder. We tour with gear (460 lbs, more after the grocery store on way to camp). We had problems some years back, gave up on bike shops and learn to build wheels, no problems since.

fooferdoggie 

thats what he found the washers he used caused the angle. he has the right nipples now to fix that, but what spokes to use? I am thinking of having the wheel that came with the bike rebuilt as the rim got damaged. that wheel was fine with 13g spokes and 36 spokes. it is a Shimano deore hub. it just may be the 32 spokes is not enough. but if I have that wheel rebuilt what rim and spokes should we use? we want tubeless and thats a limit. we can live without the v brake we dont use it that much.
he has done all the work and even replaced the spokes at no cost to me. but it may be best to use this wheel as backup or sell it new to buy a 40 spoke wheel.

LV2TNDM

You definitely have a unique problem. That's some major premature spoke failure. However, it appears your issue is clearly spoke angle exiting the nipple. Washers and/or rounded nipples may not fully rectify the problem because the nipple doesn't have THAT much freedom of movement exiting most rims (carbon being even worse). I find the wall thickness of the rim prevents the nipple from sitting perfectly in-line with the spoke angle. So what to do? Well, Jobst Brandt makes it pretty clear that spoke failure caused by spoke bend at nipple exit is a problem that should be rectified. And it's a relatively simple fix - bend the spoke! Just like seating spokes at the hub flange, you want to "cold-set" the spokes into their "bent" position instead of letting the spoke material act as a spring. When it acts as a spring, it will fatigue and fail. This is most likely your cause. (Or as mentioned, you simply had a bad spoke; unlikely though since it just so happened to break EXACTLY where you'd expect it to break with a spoke angle issue.) If you cold-set the spoke bend at nipple exit, then you eliminate the fatigue. But doing it requires a steady hand, as bending a spoke at the nipple can cause nipple damage.

And as Carbonfiberboy said, "thicker or stronger" spokes are not the solution. Contrary to popular opinion and common sense, butted or thinner spokes build a stronger wheel. And as noted, the Sapim CX Ray spoke, due to its additional forging, is Sapim's (and the industry's) strongest spoke. So that's probably your best bet. Their shape also allow the wheel builder to easily avoid spoke wind-up during building & service. However, the shape may make bending the spoke at nipple exit a challenge.

The only other question I have is if your builder is using a properly-calibrated spoke tension meter. Today's 12-speed wheels have a pretty big tension delta between drive and non-drive side flanges. If you're at or below 90kgf on the non-drive side, then this may be a contributory factor. Which spoke failed? DS or NDS? If NDS, then this may be another cause. Your builder should be able to tell you exactly what spoke tensions are on both sides after building. If not, suggest your builder start using a quality spoke tension meter. (Bike Fanatik has the sweetest model; DT/Swiss comes in second in my book.)

fooferdoggie 

the strong spokes are what Sapim recommends for e bikes and tandems.