Rim exploded on the trainer!

[kgreene10]

I was about 20’ in to my trainer workout on a Kurt Kinetic (tire on) trainer when something went pop. I assumed the tire had blown, but no, just the HED Belgium rim!

The wheels have a good number of miles on them and the brake track was becoming a little concave, though I’ve seen worse. The metal separated at what was probably the thinnest portion of the cocavity, opening about a six inch seam of metal.

Obviously, I wasn’t braking at the time, so it must have been heat build up from the tire on the resistance unit. Lucky it didn’t happen the last time I rode these outside when I descended Mt Diablo!

I’ve never heard of something like this happening before. I can imagine a tire blowing with such force that it takes out a chunk of rim, but the tire was fully inflated after the rim blew by itself. I guess it just reached the end of its fatigue life.

[tctyres]

Yeah, that's a one off. Glad you're OK, and it happened where a crash was not imminent.

I was on a tripod Cycleops mag trainer indoors once and wiped out from rocking side to side. I had to search it on the internet to see if it's a thing -- yes it is.

Your story is more interesting.

[fogrider]

The metal separates at what was probably the thinnest portion of the cocavity, opening about a six inch seam of metal.

. . . Lucky it didn’t happen the last time I rode these outside when I descended Mt Diablo!

but the tire was fully inflated after the rim blew by itself. I guess it just reached the end of its fatigue life.

kg, glad you're ok! so the rim was concave at the braking surface? I've seen aluminum rims worn to be concave. but not carbon rims! If carbon rims started wearing away, I would stop using it immediately! so since the tire was still inflated, the tube and tire was held in place by an aluminum rim? so the carbon was a structural flaring? so the carbon was hot?

[cachagua]

Just for curiosity, can you still see the little wear indicator they put in those rims? If it's still there, you might have a talk with HED... if the rim's worn to failure and the indicator still says it's good, seems like the least they'd owe you is a replacement.

[kgreene10]

Just for curiosity, can you still see the little wear indicator they put in those rims? If it's still there, you might have a talk with HED... if the rim's worn to failure and the indicator still says it's good, seems like the least they'd owe you is a replacement.

Good idea! I’ll look.

[kgreene10]

kg, glad you're ok! so the rim was concave at the braking surface? I've seen aluminum rims worn to be concave. but not carbon rims! If carbon rims started wearing away, I would stop using it immediately! so since the tire was still inflated, the tube and tire was held in place by an aluminum rim? so the carbon was a structural flaring? so the carbon was hot?

Just standard aluminum HED Belgiums.

[Peter P.]

Split rims have happened to me, and my friends, many times.

The sidewalls wear, and tire pressure perhaps combined with possible heat buildup on the trainer, do them in.

Below, you'll see an ATB rim I had split on me, and my friend Bob's rim, which split in the middle of a ride. We cobbled together a repair and finished the ride!

[sailorboy]

Even if it was not beyond the reasonable lifespan, I would wonder if they would not warranty due to use on a trainer? Not that it's right, but I wonder if that is considered somehow out of the 'normal' use

[eric01]

Some bike mfg have specific clauses in their warranty terms against trainers. But that’s for the frame. Wheels? I can’t imagine the stresses on a wheel being any greater on a trainer compared to road.

[bikinchris]

This happened a lot on tandems at one time. Another advantage of disc brakes. Somebody had to say it.

[oldpotatoe]

Actually not that rare. Saw it more than a few times in the shop. Most often rebuild because the rim was so concave but a few that blew. Most rims died by being wacked one way or another, before this happens.

[weisan]

Pictures would help.

[Black Dog]

Sounds like it could have been a combination of wear, heat build up, and perhaps high pressure due to heat build up. Check the wear indicators on the rim.

[skouri1]

Ive blown one rim from a pothole.
Rainy seasons in Seattle did them in.
Hold a card/piece of paper to the rim and see if you have concavity (on the good part :) ). I'm guessing you do. This kind of thing will happen if you push rims too far.

[unterhausen]

It really depends on where the rim blew out. For example, Velocity had some rims with extrusions that were thin at the transition from the brake track to the spoke bed that they warranties. I always figured a concave brake track was a sign that a new rim was imminent.

[Mark McM]

Sounds like it could have been a combination of wear, heat build up, and perhaps high pressure due to heat build up. Check the wear indicators on the rim.

More like a combination of wear and fatigue. The heat from a trainer will only increase the pressure slightly, and the extra temperature will only decrease the aluminum strength slightly. But using a trainer will add extra fatigue cycles.

On a trainer, the tire must be pressed against a small radius drum. As the wheel rotates, every part of the tire/rim passes through the area where it is pressed against the drum. In this area, the tire will bulge to the sides a bit, increasing the outward force on the rim sidewall. Fatigue is caused by the accumulated damage from many, many loading cycles. Every revolution of the wheel on a trainer causes a loading fluctuation on the sidewall, so every revolution can increase the fatigue on the rim sidewall.

[MaraudingWalrus]

I've seen aluminum rims worn to be concave. but not carbon rims! If carbon rims started wearing away, I would stop using it immediately!

For what it's worth, carbon rims can certainly do that, too. It just generally takes much longer than aluminum rims, as it won't flake off the same way, but can still wear down eventually.

Here (https://i.imgur.com/5f3g792.jpg) is a not very good photo of a Boyd rim that one of my regulars wore a slightly concave section into. Boyd wasn't concerned with the wear amount that was present (I can't recall how much it was, and emails don't include that detail, must have been on the phone with Boyd at the time).

It was about new wheel time for the guy anyway, as the hubs were trashed and the spoke nipples were corroding away.

I rebuilt the rims onto some fixed gear wheels, so it's not going to get any worse.

[kgreene10]

More like a combination of wear and fatigue. The heat from a trainer will only increase the pressure slightly, and the extra temperature will only decrease the aluminum strength slightly. But using a trainer will add extra fatigue cycles.

On a trainer, the tire must be pressed against a small radius drum. As the wheel rotates, every part of the tire/rim passes through the area where it is pressed against the drum. In this area, the tire will bulge to the sides a bit, increasing the outward force on the rim sidewall. Fatigue is caused by the accumulated damage from many, many loading cycles. Every revolution of the wheel on a trainer causes a loading fluctuation on the sidewall, so every revolution can increase the fatigue on the rim sidewall.

Sounds sensible and it’s something I never considered. Is there enough accumulation of wear that I shouldn’t use a decent wheel on the trainer even at the cost of buying a new cheap 11sp wheel?

[Mark McM]

Sounds sensible and it’s something I never considered. Is there enough accumulation of wear that I shouldn’t use a decent wheel on the trainer even at the cost of buying a new cheap 11sp wheel?

On a trainer, the tire is often not pressed as hard against the drum as it would be against the road, so the accumulated fatigue from riding on the trainer is probably less than riding on the road. Also, sidewalls usually don't fail until they have been worn down from braking - and you don't do much braking on the trainer. While trainers can wear down tires faster than road use, I think its safe to say that a trainer doesn't add nearly as much wear and tear to the rest of the wheel as does road use.