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Measuring rim wear?

Old 05-28-19, 09:06 AM
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Measuring rim wear?

The rim vs disc brake debate in General Cycling got me thinking. So how does one measure rim wall thickness to verify rims are still safe for those that have been used for rim brakes?

I can't seem to find a how to on this when searching. Might be searching for the wrong thing.
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Old 05-28-19, 09:07 AM
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Iwanson dental gauges are cheap and good for measuring rim wall thickness, at least above the bead seat. Here's a link to the one I got: https://www.amazon.com/Stainless-Iwa.../dp/B0087HKWCO
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Old 05-28-19, 09:12 AM
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Cheap way: https://www.ebay.com/itm/Steel-Gauge...SNN7w1-yiwUNaQ
More expensive way: https://www.ebay.com/itm/New-Thickne....c100005.m1851
Also search for "Iwanson gauge"
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Old 05-28-19, 09:15 AM
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One could also measure the diameter of a small bearing ball, put that inside the rim and measure across the ball and rim; subtract the ball diameter and you have the rim thickness.
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Old 05-28-19, 10:02 AM
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Best answer is to buy rims with a wear dimple:

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Old 05-28-19, 06:41 PM
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Say I get a dental gauge.. What's the Ok vs. Replace result I'd be looking for?
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Old 05-28-19, 06:58 PM
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When the rim begins to flex wider under the force of tire air pressure it's time to stop using that rim. The two issues usually talked about are with rim brakes any rim width variation is felt in the braking action being pulsing or grabby as the wider portions of the rim pass through the pinching brake pads. Second is the rim's brake track/sidewall cracking off the rest of the rim right at the bead seat. It's this second failure mode that is the more dangerous. Andy
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Old 05-28-19, 07:27 PM
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OK so what about the measurement? I would rather replace before I had an issue.
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Old 05-28-19, 07:51 PM
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Originally Posted by Sy Reene
Say I get a dental gauge.. What's the Ok vs. Replace result I'd be looking for?
Originally Posted by spinnaker
OK so what about the measurement? I would rather replace before I had an issue.
0.5mm is about the absolute minimum, from what I've read. But wise folks won't let them get that far: Rim thickness and wear

Another data point: my Pacenti SL23s (V2) measure 0.9mm thick at the wear indicator, so that's how far one manufacturer was willing to let a rim go.
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Old 05-29-19, 10:37 AM
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Originally Posted by spinnaker
OK so what about the measurement? I would rather replace before I had an issue.
I measured some new (un-used) rims, and they seem to all be about 1.5mm thick at the brake tracks. A somewhat used rim measured 1.3-1.4mm. Some rims I've discarded because of brake track wear and cracking measured less than 1.0mm. I'd say when the rim gets to 1.0, it's time to start thinking about a replacement. In my experience, the rim will start "thumping" as one spot on the rim begins to bulge. This is *definitely* an indication to replace the rim ASAP. I've never had a rim actually fail suddenly, but this has been known to happen and would be bad, especially on a front wheel.

FWIW, the "dental" gauge is a "crown thickness" gauge, used for measuring the thickness of artificial crowns. This instrument is accurate to 0.1mm. They are available very inexpensively, but the quality is probably pretty variable. The one I bought when I was in dental school was made in Germany and is nicely made... but still only accurate to a tenth of a millimeter. Good enough for government work!
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Old 05-29-19, 11:10 AM
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Originally Posted by sweeks
I measured some new (un-used) rims, and they seem to all be about 1.5mm thick at the brake tracks. A somewhat used rim measured 1.3-1.4mm. Some rims I've discarded because of brake track wear and cracking measured less than 1.0mm. I'd say when the rim gets to 1.0, it's time to start thinking about a replacement. In my experience, the rim will start "thumping" as one spot on the rim begins to bulge. This is *definitely* an indication to replace the rim ASAP. I've never had a rim actually fail suddenly, but this has been known to happen and would be bad, especially on a front wheel.

FWIW, the "dental" gauge is a "crown thickness" gauge, used for measuring the thickness of artificial crowns. This instrument is accurate to 0.1mm. They are available very inexpensively, but the quality is probably pretty variable. The one I bought when I was in dental school was made in Germany and is nicely made... but still only accurate to a tenth of a millimeter. Good enough for government work!


I hope you measure the crown when it is outside the patients mouth?
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Old 05-29-19, 11:16 AM
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Originally Posted by spinnaker
I hope you measure the crown when it is outside the patients mouth?
Hahaha! Yes. It's a lab procedure. The gauge is also used for measuring "wax-ups" of crowns before they're cast to make sure the metal will be thick enough.
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Old 05-29-19, 01:20 PM
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Originally Posted by sweeks
Hahaha! Yes. It's a lab procedure. The gauge is also used for measuring "wax-ups" of crowns before they're cast to make sure the metal will be thick enough.
I always wondered what the heck dentists actually did with these things.
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Old 05-29-19, 01:41 PM
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The most intense rim wear I have dealt with is back when I used rim brakes on mountain bikes. Off road use wore the braking surface much faster than anything I ever did on road bikes, and there was a bit more awareness of worn brake tracks on rims among mountain bikers, generally speaking. I don't remember ever measuring the thickness of the rim material, we would check to see if the brake surface was becoming too concave with a straight edge (you could even lay a coin across the brake surface to check). A concave brake surface indicated you had lost rim material to braking. I'm sure there were thoughts about how much concavity was acceptable, but I always just took a look at how much there was and if it seemed "excessive" I tossed the rim. As mentioned above, a manufacturer including a pre-drilled spot in the brake surface to monitor rim wear from braking is a helpful thing, too. Of course, there are many, many rims out there without those.

I've never had a rim fail because of brake track wear, fwiw.
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