Technical > Wheels, Tyres and Brakes

Andra rim cracks

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hendrich:
Hi, seeking advice or knowledge of similar occurrences. The people of this forum have much first hand experience.

I built wheels for our tandem using Ryde Andra 35 (559) rims, 36 Sapim butted spokes, and Sapim polyax nipples. Sadly, after 6000 miles of heavily loaded touring, 4 of the spoke holes in the rear wheel have developed 5 mm long hairline cracks in the rim. The spokes are not next to each other, but in very different parts. The cracks are on the obtuse angle from the spoke along the center. The wheel remains perfectly true with average tension of 105 kgf (both sides, Rohloff hub) with 15% variation. The wheel experienced no dramatic shocks during that time.

From literature, the rims are rated for (each) 130kg and tension 140kgf. Our total weight, including the bike and all gear is 210kg and the spoke tension is 105kgf. Both values are well below the maximum rim rating.

This is one of the strongest rims on the market, was this rim abnormal? The front rim has no issues. Some people suggest that 6000 mi is good under such conditions, but I don't agree. I am also considering Sapim MG nipple washers when rebuilding. I have contacted Ryde and waiting for a response. Are nipple washers commonly used for these rims?

Thanks for your comments, Mike

Danneaux:
Hi Mike,

I'm so sorry to hear of your experience with the cracked Andra rims on your tandem, the first failures of this rim I've encountered.

I have Andra 30s on my Nomad Mk2 with Rohloff hub and my Enduro-Allroad and Andra 40s on my own tandem, the latter two with derailleur drivetrains. Thorn built the Nomad wheels and I built the others. None use any washers and the spokes are sized to come with the ends at the bottom of the screw slots so the nipple is fully supported internally by the threaded spoke end. All use Sapim Polyax nipples and Sapim Race spokes.

One thing that pops out as a possible contributor is excessively high tire pressure. This is an issue I have to deal with constantly as I have a variety of stokers on my tandem and also use it for touring which includes hauling a trailer. It is not unusual to top out at 600lb/272kg for both riders, all cargo and the loaded trailer when considering a couple weeks' self-supported touring for two (26.5l/kg is typically water -- 58lbs). Unladen, the rig and riders may slot in as "light" as 350lb/159kg.

For sure, I've needed to adjust tire pressures to accommodate the range of loads and this gets very tricky when balancing the need to support so much weigh against the risks of generating excessive jacking forces against the tire bead that can be strong enough to split a rim down the centerline or fracture a sidewall. I seem to have found a compromise that works for my 26x2.0 Duremes; I run F/R pressures of 38/48psi with only myself and usual stoker on unladen day rides and boost that to as much as 45/55psi when fully laden. Under maximum load, I've never found stress cracks in the sidewalls (Schwalbe cautions this is a key indicator of running too long at too-low pressures) and the tires (miraculously!) don't appear to flatten much when viewed from the side by observers (it has so far been impractical for me to measure rim drop under load on the fully laden rig for a variety of practical reasons). I am reluctant to exceed those pressures, which correlate closely to Andy Blance's maximum recommendations in the Thorn Mega Brochure I have in my archives.

So far, I've had no problems with the Andras on these three bikes despite riding them extensively on very roughly ballasted logging roads, gravel, and cross-country, unladen or fully loaded.

Mike, could you possibly take and upload some close-up photos of the rim cracks? Though you've described the problem well, sometimes a photo gives additional insight beyond what words can convey. I think you were spot-on to contact Ryde for their take on things.

Looking forward to hearing more.

All the best,

Dan.

EDIT: I did find note of an Andra rim failure here: https://2londoners1bike.com/tag/andra-30/
This link may be helpful as well: https://www.cyclingabout.com/the-best-rims-for-bicycle-touring/

JohnR:
One potentially relevant point is that Thorn told me (in response to a question about a broken nipple) that they normally use boiled linseed between nipple and rim which acts as a lubricant and stops the nipples loosening.

B cereus:
Has the wheel been ridden in all-weather conditions?

Winter road salt  will significantly reduce the fatigue limits of aluminium alloys through stress-corrosion cracking. The drilled holes for eyelets are especially vulnerable.

Its interesting that SJS use boiled linseed oil between nipple and rim. The usual practice is to apply the oil to the spoke threads; it initially lubricates and later dries to provide a degree of thread-locking.  I imagine that applying  between nipple and rim would provide useful corrosion protection. I've seen similar recommendations to use Waxoyl around rim eyelets for corrosion protection.

hendrich:
Dan,
Thanks for the reply, I have posted a picture. There are 4 of similar size. Regarding tires... when on tour 2" Duremes (55psi), sometimes 1.5" M+ when in goathead country, and around home on day rides, 1.6" Supremes (70 psi). I also follow Andy Blance's maximum recommendations from that brochure. Prior to building these wheels, I have read all the cyclingabout.com pages on building strong wheels. That information and the Thorn brochures are the reason I use Andra's. I decided to use 35's, since they support wider tires.  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. The total weight I gave includes all our camping gear/food/water, perhaps we are 220kg sometimes (all on bike's 2 wheels).

You are higher in weight and yet have no cracking, but those higher weights are only with derailleurs? And a significant portion of that weight is on a trailer? For derailleurs (no Rohloff), the spoke angle is closer to 90 from rim and thus better nipple-rim pressure distribution.

I have also attached rim cross sections from Ryde literature models 30, 35, 40. I notice that the 30's have an additional metal bulge at the spoke holes, which may strengthen those rims against cracking, but max specifications are the same 1400N, 130kg/tire. 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.

Regarding other peoples comments, I used oil on the threads and the spokes have not been exposed to salt.

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