Racing Line BB30 Cranks

[PeterH]

This is a shot in the dark, but I was gifted a set of the fancy Racing Line BB30 cranks a while back but warned that they were recalled because some of them broke. I'd like to give them a go, but want to be careful, does anyone know how and where they were breaking so I can keep an eye on them?

Much appreciated.

[Mark W]

They were breaking because the design was shit, basically. From memory cracks would develop between the hexagon cut-outs in the back of the crank arms, and then they'd snap. You can run them, but you'll need to watch them carefully.

[PeterH]

That is the info I was looking for, thank you Mark.

And yeah, machining out sharp corners right there seems like a bad idea, darn I was hoping to have some fun with these but back to standard cranks it seems.

[The dab]

Would any dremel work alleviate/stop any cracking? 

[Mark W]

 

That's what he's working with. There's so little material in there anyway that although removing some to round things out might help in one way, it would probably be detrimental in another. To be fair though, there's a large part of me that just wouldn't run CNC-only (rather than forged then CNC'd) lightweight trials cranks, so adding in all the other factors I would just be throwing them in the recycling bin in all honesty.

[PeterH]

Once again nice work Mark. I looked for an image to put in the original post and couldn't find one and you grab one from a shop just one state over from me.

I don't think ruling out all CNC cranks is a hard and fast rule, depending on what size plate they were hogged out of they may be pretty good, but without extra info I would say forged is a better option. I had also thought about looking into trying to take out the sharp corners if I knew exactly which ones they broke at, but looking at the design the best that would do is buy a little time, not solve the problem at all.

This is the kind of stuff I really like, it is the total intersection of what I do for a living and what I do for fun. I used to talk with an old mentor every Monday when he would ask if I broke any bike parts over the weekend and we would look at the fractures and learn what we could.

[Mark W]

That Webcyclery pic took some finding to be fair! Those cranks are about as illusive online as they are in real life now it seems.

You're right about CNC-only cranks - there are some applications where I wouldn't have issues running them, and that decision would certainly be design based too. It was more that for me, a lot of trials cranks are just CNC'd because it's the cheap option, and the lack of any real testing from the majority of trials brands means the customer is the one who gets to find out just how strong they really are.

Things are better now than they were when those Racing Line cranks came out, but some of that is just because a lot of the sketchier brands have fallen by the wayside now. Trying to beat established competition on simple metrics like weight was the way everyone was going, and the only way to really do that is just to cut more material out. It always seemed ironic to me that there was a switch to a larger axle standard partially under the guise of improving strength and stiffness, but then they'd hack all the material out of the crank arms and make them weak and flexy instead.

There's a lot to be desired with the way the trials industry is currently (we really don't need 5-6 different front axle standards, and Jitsie's tapered steerer standard needs to get in the sea), but the way that there's been an increased focus on durability over simply dropping weight is one of the better aspects of it. 

[SergeL]

This is how badly cracks could go:

[La Bourde]

Hope the rider was not injured!

Looks really nasty.