It's been a long time since I've had to deal with a cracking rim. Back then, my sidewall failed under heavy braking, and it prompted me to write an article about measuring rim sidewall thickness (which turns out to be one of the most popular posts on this blog...).
This time around it wasn't wear that made my rim crack and it wasn't the sidewalls that were affected. A few weeks ago, when changing tires, I noticed cracks around several spoke holes. The wheels had come to me used, and I had been riding them for several years and thousands of miles. In the back of my mind I recalled reading complaints about this specific model of rim, the made-in-Australia Velocity Synergy OC rims. This was one of the rims that was available in 650B size early on, and the off-center design made it nice to build with. Some googling confirmed: The Synergy OC indeed had a history of people reporting cracking at the spoke holes (you have to scroll down quite a bit to the relevant post), maybe due to excessive spoke tension, maybe not. I had no idea how long the cracks had been on the rim. Early on in my ownership I had to replace a broken spoke, and a few weeks ago I felt a slight wobble in the wheel. But I attributed that to a badly seated tire -- the other thing that Synergys were known for was loose tire fit. In full avoidance mode I decided to deal with this once the season was over.
That didn't quite work out. On a leisurely ride on Saturday, I suddenly a pretty bad wobble on the rear wheel. I immediately knew was up, and visual inspection confirmed it: The cracks no longer were just around the holes but had started pulling out sections of the spoke bed. I made it back home alright, but immediately took the wheel apart.
What to rebuild with, though? Fortunately there are still a bunch of 650B options for rim brakes available, e.g. the HED Belgium, Velo Orange Voyager, or Pacenti Brevet. But hoarder that I am, I actually have a pair of brand new 650B rims sitting in the basement. These are Pacenti SL23s, which I had gotten at a sale many years ago. Convenient, isn't it? Well, except for one thing: The SL23 also has a reputation for cracking at the eyelets.
I have another wheelset with SL23s, and they have been working just fine for years. So I'm willing to take the risk. The wheel has been built. Now we'll have to see how they'll hold up.
