saturnhr

Since rims wear over time due to brake pad abrasion, is there a common agreement on minimal sidewall thickness on aluminum rims?
Thanks

Spoonrobot 

Rim wear (Jobst Brandt)

saturnhr

part B to the question: can you just ride until it breaks/ splits or separates - or are there catastrophic failures possible (tire jumping off in corner or similar)?
Thanks again

dsbrantjr

Some rims have grooves or small drilled holes in the brake track to act as wear indicators; when those wear away it is time to look for a replacement. You can also place a straightedge across the brake track to check for concavity which might indicate that the rim is beginning to bow outwards. You can also deflate the tire and measure the brake track thickness with a caliper or micrometer. Probably something like 1mm might be a reasonable guideline, or 50% or 60% or of the as-new thickness if that is known.

Edit: Dentists make similar measurements and they have gauges which can be used to "reach around" the hooked part of the rim to measure the brake track thickness directly; Iwanson and Boley gauges are two types. They can be had online for under $10.

https://www.amazon.com/Stainless-Iwan.../dp/B0087HKWCO
https://www.amazon.com/Stainless-Stee...S6W7V6KVQYV2JT
https://www.amazon.com/Euro-Tool-Bole...S6W7V6KVQYV2JT

Jeff Wills

I would not ride it until it splits. That will result in a blow-out (at least) and a long walk home. When mine let go, it was only about 10 miles from when the rim started bowing out until the time it blew.

From Rites of Spring 2005

vintage cellar

Maybe email Velocity USA and they might give you a ballpark figure to not go beyond.

FBinNY 

There's no single answer because the "hoop stress" of the tires pulling out against the flanges is proportional to the tire's width and pressure. So, a 32mm tire needs 30% more rim strength for the same pressure as a 25mm tire. So even if we wanted to calculate the minimum thickness, we don't have enough info.

When the rims on my commuter started getting thin to where I started thinking about it, I adopted a "safety method" when pumping tires. I'd pump to about 15-20% higher than the intended riding pressure, then bleed them down. My theory (not proven) was that the higher stress would crack the rim if that were going to happen, then dropping would give me some safety margin. In then end I never got conclusive results proving or disproving my logic because a nice lady put both wheels out of their dotage by T-boning me. (no injury to me but the wheels were toast).

rydabent

Best reason for disc brakes.

Retro Grouch 

Sometimes I feel like a analog man who is trapped in a digital world. Feel the brake track with your finger. If it feels noticeably concave, you're due for a new rim.

Newer rims, at least rims that are sold in Europe, have wear indicators. One common type is a groove machined around the circumference of the rim. When the brake track wears down to the bottom of the groove, you're due. Some just have little dimple holes drilled on the outside of the rim. Some have what look to me like gouges on the inside surface of the rim. When the rim wears through to the gauge it scares most people enough that they want a new one.

FBinNY 

I'm with you and never bothered measuring, since I had no reliable way to know the limit. In that vein, I suspect that any wear indicators are going to be conservative, especially with relatively narrow tires.

But I feel (or like to believe) that my safety method would have worked to advantage if/when it got the chance. Others also report slight changes in rim width as the thinned material begins to flex out under load. That cause brake pulsing that might give adequately early warning.

These days everybody seems to want rocket science precise answers, but some things have too many variables for that, so you have to rely on observation and common sense.

fietsbob

if its a new rim remember what it looked like then ... you can see the wear in a brake track over time ..

those dental calipers will help you collect data..

And, you can grind a notch in the jaws of a proper caliper to reach around the bead hook in the edge of a rim

to measure the thickness below it, then get 10ths of a MM data..

saturnhr

Thanks for all the educated answers above!
I liked to hear the o.5mm Jobst Brandt quote, I further will apply the "feel for concave" and "the blow up above method", and I will take measurements.

I am in charge of 2 wheel sets I am concerned about, one 10 speed Dura Ace wheel set I bought for cheap, where a bike shop professional told me, the wear was at its end (interestingly my son owns a new dura ace 11speed wheel set (with similar rims), I will take comparative measurements.
The second wheel set are old Mavic open cd4 anodized rims with the anodization on brake surfaces long time gone. I assume there is no new one to compare to.
Will post measurement, but will take me a while, since above mentioned rims are not all same location
Thanks again!