Spoke Bed Failure –Mavic Open Pro

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Mavic Open Pro, spoke bed cracked near 11 out of 32 spoke. Eyelets broken on 9 of 11 holes with cracks.

Note hole 9 has cracks far to either side of the spoke hole, on both sides. Other cracks seem to be only at the hole.

Rim weighed about 412 g after failure. There is no significant brake track wear, but several eyelets are missing. Claimed weight is 425 g, rider-reporeted weights typically 425 -435 g (as of 2011/07)

Rim was laced to a Rohloff hub, so spoke tension was nearly symmetrical. Cracked at holes #1, #2, #6, #8, #10, #12, #14, #20, #22, #28, and #30. (Numbers shown in photos are the N'th hole cracked — "1" is hole #1, "2" is hole #2, "3" is hole #6, "4" is hole #8, and so on.) It seems surprising the cracking is mostly on one side, given the wheel has nearly symmetrical spoke tension.

Spokes were DT 2.0/1.8/2.0 mm. Spoke tension at build and at fail unknown; builder has built wheels lasting up to 60,000 km without spoke hole cracks. Wheel was re-trued at one point and several spokes were substantially loose, none substantially tight.

The problem was noticed due to noise while riding, after about 17,500 km use.

Bike + rider + gear about 90 kgf. Typical riding is hilly with a "sit and spin" riding technique, but with enough vigor to almost always stay out of the Rohloff low range.

Various Mavic rim models have a reputation for being light, stiff, and for failure by cracking. This suggests an especially thin section compared to other rims. Note extrusion dies wear significantly in service, so the first rims from a given die have significantly less material than later rims from the same die.

It seems significant so many eyelets failed, and in many cases some of the fracture lines correspond to an edge of the cracked eyelet. Assuming they are related, it is unclear which failure was first. Did cracked eyelets cause cracked rim material, or did cracked rim material cause cracked eyelets?