Technical > Wheels, Tyres and Brakes

Andra rim cracks

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mickeg:
I was unaware of the MG nipple washers.  After reading a few internet sites I can see where the MG washers would be a good idea on a rim built for heavy duty use, especially with high spoke tension.   

On one of my bikes I used Sapim nipple washers on the drive side on the rear wheel on a derailleur bike.  These are what I used.  I do not recall them as being called an HM, I thought they were the only Sapim nipple washer available.
https://www.bikehubstore.com/Sapim-Nipple-Washer-Round-PolyAx-p/spw-hm.htm

I have used Sapim nipples on all my wheels since I built my Nomad eight years ago.  That said, I have always been a bit nervous that the nipple shape is analogous to being a wedge that could cause a rim crack.  The HM washers should alleviate any problem with the Sapim nipple wedge shape.

If you use nipple washers, adjust your rim ERD in your calculations for spoke length.  In my case I found that I could use the same spokes on the drive side and non-drive side on the wheel I was building if I used the older style (HM) nipples on the drive side because of the way that the washer thickness changed the ERD that I used for spoke length calculations.  That is why I used the nipple washers on that wheel.

Side note - I have often heard people refer to nipple washers as spoke washers.  So, be careful with word choices, as some people confuse the terms.

Danneaux:
Hi Mike!

--- Quote ---In the link you sent, I believe they cracked a (DT swiss?) EX rim and replaced with Andra 30s, i.e. the Andra's did not crack.
--- End quote ---
You're absolutely right; I should have read more carefully before posting the link in haste.  :)

--- Quote ---You are higher in weight and yet have no cracking, but those higher weights are only with derailleurs?
--- End quote ---
Yes, the tandem at present has a derailleur drivetrain with a Rohloff waiting in replacement. The current hubs are Suzue high flange, about 73mm as I recall, but still much smaller in diameter than a Rohloff so spoke angles are indeed less severe. The freewheel hub is double-threaded and a heavily used Arai drum/drag brake is on the offside, so the spokes and rims are subject to braking as well as drive forces. No problems to date.

--- Quote ---And a significant portion of that weight is on a trailer?
--- End quote ---
My Danneauxbuilt 2-wheel trailer weighs 17lbs/7.7kg empty with hitch assembly. Full, the trailer has weighed up to 125kg/56.7kg...usually split between water and food for two. Tongue weight carried by the tandem's rear axle is a fraction of that, usually about 10-15% depending on how the load is distributed in the trailer.

--- Quote ---The 40's hole surfaces appears to be planar, relative to the 35's, and so nipple washers on the 35's may not work well.
--- End quote ---
<nods> I see your reasoning in thinking the nipple washers might distribute the stress over a larger area, but I am concerned a) they will be incompatible with the 35's internal profile as you are, and b) they seem likely to offset the advantage of the rim's directional drilling.

As mentioned, I have Andra 30s on two of my singles. I decided to bypass the 35 in favor of the wider 40 for my tandem, the goal beong to maximize internal spacing between the sidewalls, so I did not spend a lot of time researching the 35s. When looking to source the 40s, I did find some listed "Rohloff-specific" directional drillings and others simply mentioned only "directional drilling" and a "smart bead" for the nipple (keeping in mind some of the ad copy was machine-translated from German to English). I'm not at all sure they are the same.

Mike, did you use Sapim's Polyax nipples? They have a rounded profile that nicely matched the dimpling on my Andra 30 and 40 rims.

Yes, the photos helped a lot, thanks. It brings to mind two memories from my past wheel builds, both having to do with the notch-sensitivity of aluminum:

1) Back in the day, Mavic produced a couple of classic box-section road rims, the MA-2 (polished) and MA-40 (hard anodized); both had clinched ferrules. While the MA-2s lasted forever (I am currently running a pair with more than 32,000mi/51,500kms on them), the MA-40s had a tendency to crack where the ferrules were clinched into the hard anodizing, creating a notch where cracks originated and then propagated from.

2) A lot of early 1980s touring bikes used Araya 16A(3) or 16A(5) rims. These used a channel section similar to the old Wolber Super Champion Mod. 58 -- but without ferrules. When these were supplied OEM in factory-built wheels, the spoke tension was usually on the loose side and the rim had no problems with cracking. However, a few of my bike shop friends increased tension and began to find longitudinal cracks starting at the rim holes. When I undid the nipples, we found they had gouged crescents into the rim's inner surface and that where the cracks began. Of course, these were machine-built wheels and no lubrication was used in the build, so the gouging may have been a direct result of the process as much as the design. I had no problems with the one I built.

This is not a universe of cases, but it makes me wonder of perhaps your rim might have had some burred spoke seats or perhaps the nipples you used might not have been fully compatible with the seat profile. Just a thought. It'll be interesting to hear what Ryde says in reply to your inquiry.

hendrich:
Mickeg,
Thanks. I have attached cross section pictures of Sapim MG and HM washers. Agreed, these are nipple not spoke washers. The conical shape of the HM washer presumably mimics the spherical shape of the polyax nipple, and so I guess someone could use the HM washer with regular nipples to achieve better nipple angulation.

The Sapim MG washer seems ideal for my application. Based on the rim cross sections, it appears that the Andra 35 bed is not as planar as the 40 bed. However, the non-planarity is small for a 7.5mm washer, and the washer may conform (bend) a bit to the non-planar surface. The polyax nipples can still rotate in that washer as needed and then the washer expands the pressure contact area of the rim. Seem right?

It is difficult to find the MG washers. The places I can find on web are all in UK, so may order from there.

Dan: I was careful to deburr the spoke holes before building. With polyax nipples

martinf:
I've sometimes used brass spoke washers under spoke heads when building on steel-flanged hubs (notably old Sturmey Archer).

Not sure if it made any difference or not as sometimes I have built similar wheels without and they have been fine.

I've never used spoke nipple washers yet, but a quick web search found this : https://www.sapim.be/tools/washers which doesn't show the MS and MG washers.

The round nipple washers appear simply to be 5 mm stainless steel washers, which I already use in three or four outside diameters for various bike-related things. The biggest outside diameter is particularly useful when bolting stuff (such as mudflaps) onto thin metal or plastic mudguards, so I imagine it would spread the load of a spoke nipple quite well on a rim with a flat profile such as an Andra 40. I recently got 2 of the latter to use when any of my current 26" rims wear out, so I will probably try round washers then, taking account of Mickeg's remark on adjusting the spoke length calculation.
 

mickeg:

--- Quote from: martinf on October 31, 2021, 03:27:32 pm ---...
The round nipple washers appear simply to be 5 mm stainless steel washers, ...

--- End quote ---

I think that is a brilliant idea, thanks for mentioning that.

Next time I am removing or adding a nipple to a spoke, I will need to experiment a bit.

As I noted above, I have had a concern that the shape of the Sapim nipple could act as a wedge, if just putting in a flat washer would reduce the stress on the rim, I would be all for that.  And a 5mm flat washer is of minimal thickness.  I do not know if the ERD that I used for my Andra 30 rims was off slightly, but the spoke length I used on my Rohloff wheel would probably have to be the next longer size if I used any nipple washers on that wheel.  I have a few threads showing at the top of each nipple.

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