Bicycle Mechanics - how to evaluate the severity of this "crack" inside rim

I have found what appears to be a crack running along the inside of my wheel. There is no damage to the sides (braking surface), the edges of the rim (metal meets rubber), or the other side of the surface (where the spokes thread in).

Is this something that use/abuse has caused? Is this something that must be fixed immediately? Is this even a structural "crack" rather than a scratch or surface blemish from tire tools?

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I tried searching the forums and google but the threads I found discussed cracks along the braking surface and when the spokes are pulling away from the wheel. I can seem to figure out the proper search terms for my specific issue. Thank you.

Interesting. Are the spoke holes blind?

I suspect this isn't cracking because without the stress of the spokes (nipples) there's no reason for this kind of longitudinal crack to form, unless the area is thin enough that the lateral tire pressure is pulling it apart.

There's an easy test got that. Make a C shaped gauge from an old credit card, or use a caliper to measure rim width. The gauge should be about 1mm wider than the rim without the tire. Mount the tire and inflate to full pressure and see if the rim widens and by how far. Anything close to 1mm could mean that the tire is pushing the rim apart in the middle.

If you can't detect widening of the rim with tire inflation, then it's probably fine to ride.

As for scratches you made mounting a tire, I don't see nicks at the edges where most of that sort of damage would occur, so i doubt that that's it.

I don't know enough to answer the question of whether the spoke holes are blind.
If you mean do the spoke holes thread in on one side but don't come completely through the wheel, then that appears to be the case.
If that question depends on the manufacturing process, my wheel is a dura ace wh-7850.

I don't have a caliper so I'll try that credit card trick in a few minutes.
What do you mean by "without the stress of the spokes (nipples)"?
I understand you to be saying that without spokes this kind of pressure wouldn't occur, but the spokes are on the wheel. Or do you mean that unless someone tightened the spokes when truing the wheel that kind of damage would not normally occur?

I'm sorry, I'm just not able to visualize the concept you are trying to relay to me because the terminology is new to me.
(On that note, I have no idea how to create a credit card c-clamp but I've got a bunch of old cards to ruin experimenting!)
Finally, is this something I can or should bring up with Shimano since this possible damage is occurring without any visual damage to the outside or edges?

By "blind" I mean that the spoke or nipple holes don't go all the way through the rim as they do on "normal" rims. By extension if the spokes aren't supported by the area where the cracks are, then it isn't spoke stress that's causing them.

If the wheels are relatively new, and are in fact cracking down the center well, I'd bring it up with Shimano and see what they have to say. One possible cause of this cracking could be the combination of high pressure and large cross section tires. The tire pressure side stress is proportional to the inflation pressure times the width of the tire.

Thank you for the help. Unfortunately, the credit card trick revealed that it does expand when under pressure and I confirmed it by spinning it with the brake set correctly and it stops when it hits the affected area. So that's a huge bummer :(

shimano has a 1 year warranty on their wheel sets. Try them.

Thank you for the help. Unfortunately, the credit card trick revealed that it does expand when under pressure and I confirmed it by spinning it with the brake set correctly and it stops when it hits the affected area. So that's a huge bummer :(

So at least a good diagnostic confirmed the problem, and you know the wheel is toast. It's the first failure of this type I've ever seen, so Shimano should at least be curious and want to see it, and if the wheel isn't old or otherwise beat up will probably do right by you.

What pressure do do you inflate hyoru rtieres to? Many rime have limits of 100 to 110 bs

What pressure do do you inflate hyoru rtieres to? Many rime have limits of 100 to 110 bs
Severe overinflation should blow the tire bead off the rim way before actually cracking the rim itself. The OP's wheel has a structural or manufacturing defect that isn't the result of tire pressure.

Tubeless type rim?

Severe overinflation should blow the tire bead off the rim way before actually cracking the rim itself. The OP's wheel has a structural or manufacturing defect that isn't the result of tire pressure.

Yes, and no. Hoop tension is the product of pressure and cross section. It's very possible for a wide tire to over stress the rim while still staying within it's rated pressure. Likewise, Shimano designs the rim around an expectation of how much hoop strength will be needed. Weight constraints keep makers from overbuilding, so if Shimano intended this rim for a 25mm tire at 120psi max, a larger tire would over stress it.

So whether it's a defect, or-user overstressed depends on what Shimano intended, and what the user actually used. I'd still let Shimano decide and/or explain.

BTW- the design strength vs defect issue is something we see coming up more and more often, as makers keep pushing to keep top end bikes light, and users are growing heavier (on average, especially in the USA) every year. No one expects a sports car to handle the load of a small pickup, yet we expect bikes designed for 160# racers to handle whatever riders can throw at them. Something has to give, and it seems to more often every year.

Thanks all for your responses. I took my wheel down to my local shop and the tech told me to call shimano. But as I was walking up to the counter to check on the status of an order one of the sales guys asked how I was doing. Told him crappy and showed him my wheel. He told me the rep was hanging out around in the store and to give him a minute. Came back, asked me to grab my front from home, come back and they'd be replacing and uprading me!

When I asked what I could have done differently, I was told I didn't cause it.

...the rep was hanging out around in the store and to give him a minute. Came back, asked me to grab my front from home, come back and they'd be replacing and uprading me!

When I asked what I could have done differently, I was told I didn't cause it.

If you need good customer service the company road reps are almost always the most customer friendly. Glad to hear it turned out OK for you.

Tubeless type rim?
Sorry, I didn't see your question until I came back to the thread to update the status.
Yes, the cracked wheel was a scandium tubeless clincher type rim.


The shop replaced those with the 2012 version and I believe these have a three year warranty.