Jim’s Tech Talk
By Jim Langley
This week I’m sharing photos of what I think is a fascinating wheel collapse or as chefs say, “deconstruction” might be a more appropriate word for what happened.
Follow-up on Chain Keepers
But first, a couple weeks back we were talking about getting a dropped chain back on when a bike has a chain keeper (a device designed to keep the chain on that can still allow the chain to drop under dire circumstances).
I just wanted to let you know that there was so much interest in that story that I decided to make a separate video about installing a road bike K-Edge chain keeper. Here it is below. And, since several folks already asked, the video is about braze-on/bolt-on front derailleurs. If you need a keeper for a clamp-on (band-type) front derailleur on a standard round tube frame, Deda Elementi makes the Dog Fang (great name) https://amzn.to/3Myo4sK It’s easy to install and adjust.
Now for Mike’s wheel story. Please refer to the photos as you read along, weigh the evidence and see what you think happened. There are some obvious lessons (don’t hit things in the road) and maybe some other things worth remembering.
Mike is a Santa Cruz roadie friend of a friend of mine who sent him my way for advice. When I talked to Mike on the phone he said he’d had a bad accident in which he broke one elbow and almost broke the other too. He explained that he somehow didn’t see a stick on the road and when he hit the stick his front wheel collapsed. He said he didn’t have any time to react and he fell straight down onto the pavement landing on his elbows!
You can see the stick in the first photo. Look closely and you should be able to see the black marks in the stick from the spokes. From the way the spokes marked up the stick and from the fact that there didn’t appear to be any marks on the front of Mike’s carbon fork, I believe the stick got flipped into the wheel when Mike hit it and then it jammed sideways between the fork and spokes.
But Mike didn’t get thrown over the bars, he was dumped straight down onto his elbows. So I think the wheel must have kept turning while the stick was still in the fork. Some spokes are bent and some of the aluminum nipples are torn, too, which indicates that a lot of force pulled on both.
In photo two notice that the wheel basically came apart at the hub. It’s built with direct-pull (also called “straight-pull”) spokes. Mike’s have wedge shaped heads that fit into pockets in the hub. The hub is slotted to receive the spokes. When the wheel is tensioned the spokes are held in place in the hub by the spoke tension and by how the spoke heads fit into the pockets.
There are direct-pull spokes that pass through the hub so that they’re held captive in the hub and can’t come out unless they break or the spoke nipple comes off. But Mike’s hub is slotted meaning when loose the spokes can come out of the hub.
There are plastic dustcaps that snap over Mike’s hub. One is shown in photo three (the one that belongs on the other side got lost in the crash). The dust caps are what ensure that the spokes can’t come out of the hub if the wheel suddenly loses tension. Notice that the one dustcap still there is loose on the hub now. Also look at the hub spoke hole at about 12 o’clock on the hub. Notice how it’s stripped or spread open.
Looking at everything I think what happened is:
- Mike hit the stick and it got sucked up by the wheel and jammed between the fork and spokes.
- The bike kept rolling and as it did so several spokes ran into the stick which put so much force on the spokes that their ends were yanked out of the hub holes, ruining the hub in the process.
- Here’s where it gets interesting. A few loose or broken spokes won’t cause a wheel to collapse. But when Mike’s spokes got yanked out of the hub, the ends of the spokes must’ve been shaped just right to pop off the very dust caps designed to keep the spokes in the hub.
- The result was that the wheel lost almost all spoke tension and almost every spoke came out of the hub as you can see in photo 4
What I find amazing is that it happened so quickly. Mike said he only had a second or two to react and he also said he was only going about 12mph. I would have expected it to take several revolutions for any wheel to come apart like this. But I believe it happened the way he said it did.
Am I Right?
I look forward to your comments on whether you agree with my theory or have another one. I also think it’s worth considering what wheel lessons can be learned from this. As I said at the start, we can never be too cautious about avoiding things in the road. But, equally important I think is the quality of the wheels we choose to ride.
The problem is, how could Mike or his mechanic or the bike shop have known that those plastic dust caps weren’t up to the task of keeping the spokes in during such a crazy calamity? I don’t think they could but the wheel manufacturer should have, don’t you think? If nothing else, now we know to look even more closely at how spokes are held in our wheels!
And what about Mike? He’s healing and looking forward to getting back to riding with some different wheels.
Jim Langley is RBR’s Technical Editor. A pro mechanic & cycling writer for more than 40 years, he’s the author of Your Home Bicycle Workshop in the RBR eBookstore. Tune in to Jim’s popular YouTube channel for wheel building & bike repair how-to’s. Jim’s also known for his cycling streak that ended in February 2022 with a total of 10,269 consecutive daily rides (28 years, 1 month and 11 days of never missing a ride). Click to read Jim’s full bio.
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