Rim failure

I was riding my MTB when the rear brakes locked up.

While investigating, the tire blew up.

It sounded like a gunshot. Tires were at 50 p.s.i.

At first I thought I just had a flat.

But I noticed the rim had separated from the wheel on one side.

The bike tech said my brake wore thru the rim.

Is there a way to foresee rim failure?

Thanks,
Andy

On Wednesday, March 3, 2021 at 1:46:53 PM UTC-6, AK wrote:
I was riding my MTB when the rear brakes locked up.

While investigating, the tire blew up.

It sounded like a gunshot. Tires were at 50 p.s.i.

At first I thought I just had a flat.

But I noticed the rim had separated from the wheel on one side.

The bike tech said my brake wore thru the rim.

Is there a way to foresee rim failure?

Thanks,
Andy
Sorry about the double post.

:-)

On Wednesday, March 3, 2021 at 1:46:53 PM UTC-6, AK wrote:

Is there a way to foresee rim failure?

Thanks,
Andy
Apart from measuring the rim thickness, in my experience the rim will start to "thump" when the brake is applied. That's the signal to start planning for a new rim.

On Wednesday, March 3, 2021 at 5:23:04 PM UTC-8, Steve Weeks wrote:
On Wednesday, March 3, 2021 at 1:46:53 PM UTC-6, AK wrote:

Is there a way to foresee rim failure?

Thanks,
Andy
Apart from measuring the rim thickness, in my experience the rim will start to "thump" when the brake is applied. That's the signal to start planning for a new rim.
I'm not really sure about this. Aluminum rims are made in a long single molding and then rolled into a wheel. Sometime the manufacturers do a bad job of matching the ends of the molding and they will start thumping long before there is any appreciable wear on them. I have spoked up many rims like that. You can correct it a little with spoke tension but it always returns.

On 3/4/2021 11:49 AM, Tom Kunich wrote:
On Wednesday, March 3, 2021 at 5:23:04 PM UTC-8, Steve Weeks wrote:
On Wednesday, March 3, 2021 at 1:46:53 PM UTC-6, AK wrote:

Is there a way to foresee rim failure?

Thanks,
Andy
Apart from measuring the rim thickness, in my experience the rim will start to "thump" when the brake is applied. That's the signal to start planning for a new rim.
I'm not really sure about this. Aluminum rims are made in a long single molding and then rolled into a wheel. Sometime the manufacturers do a bad job of matching the ends of the molding and they will start thumping long before there is any appreciable wear on them. I have spoked up many rims like that. You can correct it a little with spoke tension but it always returns.

Learn the vocabulary. "Extrusion" not "molding."

--
- Frank Krygowski

On Wed, 3 Mar 2021 11:46:51 -0800 (PST), AK
wrote:

Is there a way to foresee rim failure?

Yes. Use one of these:
https://www.google.com/search?q=crystal+ball&tbm=isch
Properly calibrated, it will also provide insight into other future
events.

If you want to predict when your rim will fail, measure the rim
thickness when it is new, and at various times over the years that you
ride on the wheel. Record the miles your ride between measurements.
Draw a graph and extrapolate the curve to the point where it will be
the thickness of the rim that just failed. You probably want a safety
factor, so extrapolate to a thicker and safer thickness than the point
of failure.

If you're into high tech (this is a tech newsgroup), you might
consider purchasing a ultrasonic thickness meter. These will measure
aluminum (and other things) down to about 1.2mm. The bulk of the cost
is in the probe, so if you buy used, make sure the probe is good:
https://www.google.com/search?q=ultrasonic+aluminum+thickness+meter&tbm=i sch
https://www.ebay.com/sch/i.html?_nkw=ultrasonic+thickness+meter
I don't own one of these (yet), but have borrowed several over the
years. My no-name 26" rims measure 3.0mm, so a 1.2mm minimum
measurement device should work.

However, if you're cheap and lazy like me, just deflate the tire, push
the tire and tube to one side, and use calipers to measure the rim
thickness.
What I wanted:
https://www.grainger.com/product/MITUTOYO-4-Way-Digital-Caliper-1ARG3
What I bought:
https://www.ebay.com/itm/6-150mm-Carbin-Fiber-Electronic-Digital-Vernier-Caliper-Micrometer-Guage-LCD-US/113928534251
The on/off switch on the cheap calipers does not fully turn off the
electronics, so the battery will drain prematurely. Remove the
battery when you're not using it, buy plenty of spare LR44/AG13
alkaline cells, or use 357/SR44/357/A76 silver oxide cells, which last
longer.


--
Jeff Liebermann
PO Box 272 http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann AE6KS 831-336-2558

Jeff Liebermann wrote:
On Wed, 3 Mar 2021 11:46:51 -0800 (PST), AK
wrote:

Is there a way to foresee rim failure?

Yes. Use one of these:
https://www.google.com/search?q=crystal+ball&tbm=isch
Properly calibrated, it will also provide insight into other future
events.

If you want to predict when your rim will fail, measure the rim
thickness when it is new, and at various times over the years that you
ride on the wheel. Record the miles your ride between measurements.
Draw a graph and extrapolate the curve to the point where it will be
the thickness of the rim that just failed. You probably want a safety
factor, so extrapolate to a thicker and safer thickness than the point
of failure.

If you're into high tech (this is a tech newsgroup), you might
consider purchasing a ultrasonic thickness meter. These will measure
aluminum (and other things) down to about 1.2mm. The bulk of the cost
is in the probe, so if you buy used, make sure the probe is good:
https://www.google.com/search?q=ultrasonic+aluminum+thickness+meter&tbm=i sch
https://www.ebay.com/sch/i.html?_nkw=ultrasonic+thickness+meter
I don't own one of these (yet), but have borrowed several over the
years. My no-name 26" rims measure 3.0mm, so a 1.2mm minimum
measurement device should work.

However, if you're cheap and lazy like me, just deflate the tire, push
the tire and tube to one side, and use calipers to measure the rim
thickness.
What I wanted:
https://www.grainger.com/product/MITUTOYO-4-Way-Digital-Caliper-1ARG3
What I bought:
https://www.ebay.com/itm/6-150mm-Carbin-Fiber-Electronic-Digital-Vernier-Caliper-Micrometer-Guage-LCD-US/113928534251
The on/off switch on the cheap calipers does not fully turn off the
electronics, so the battery will drain prematurely. Remove the
battery when you're not using it, buy plenty of spare LR44/AG13
alkaline cells, or use 357/SR44/357/A76 silver oxide cells, which last
longer.



Vernier calipers alone won’t do it because the rims wear concave on the
outside. I’ve jammed a piece of copper wire between the center of the rim
track and my caliper, and then subtracted the thickness of the wire in
order to measure the thinnest part of the rim.

AK wrote:
I was riding my MTB when the rear brakes locked up.

While investigating, the tire blew up.

It sounded like a gunshot. Tires were at 50 p.s.i.

At first I thought I just had a flat.

But I noticed the rim had separated from the wheel on one side.

The bike tech said my brake wore thru the rim.

Is there a way to foresee rim failure?

Thanks,
Andy


I generally went by how concave the rim had got! It’s been quite a few
years since my MTB where rim brakes, but that was how I generally judged
it.

Roger Merriman

On Thu, 4 Mar 2021 20:34:48 +0000 (UTC), Ralph Barone
wrote:

Jeff Liebermann wrote:
However, if you're cheap and lazy like me, just deflate the tire, push
the tire and tube to one side, and use calipers to measure the rim
thickness.
What I wanted:
https://www.grainger.com/product/MITUTOYO-4-Way-Digital-Caliper-1ARG3
What I bought:
https://www.ebay.com/itm/6-150mm-Carbin-Fiber-Electronic-Digital-Vernier-Caliper-Micrometer-Guage-LCD-US/113928534251
The on/off switch on the cheap calipers does not fully turn off the
electronics, so the battery will drain prematurely. Remove the
battery when you're not using it, buy plenty of spare LR44/AG13
alkaline cells, or use 357/SR44/357/A76 silver oxide cells, which last
longer.

Vernier calipers alone won’t do it because the rims wear concave on the
outside. I’ve jammed a piece of copper wire between the center of the rim
track and my caliper, and then subtracted the thickness of the wire in
order to measure the thinnest part of the rim.

Thanks. You're correct. I forgot about the concave wear pattern,
even though it was mentioned in the previous thread on the same topic.

It would probably be better to use a micrometer or dial thickness
gauge with ball tips. Flat tips would still be a small problem with a
concave wear pattern, but since the tip diameter is much smaller, the
error would also be much smaller. Something like this:
https://www.starrett.com/metrology/product-detail/1015MA


--
Jeff Liebermann
PO Box 272 http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann AE6KS 831-336-2558

On Thu, 04 Mar 2021 08:49:17 -0800, Tom Kunich scribed:

I'm not really sure about this. Aluminum rims are made in a long single
molding and then rolled into a wheel.

Err, I think you'll find they are an extrusion, cut to length and then
'rolled and joined.

Sometime the manufacturers do a
bad job of matching the ends of the molding and they will start thumping
long before there is any appreciable wear on them. I have spoked up
many rims like that. You can correct it a little with spoke tension but
it always returns.