Blowout on rear tire

On 27/02/2021 04:30, AK wrote:

Today while riding, my rear brakes locked up.

While investigating, the rear tire blew up causing part of the rim on one side to split off.

The tech at the shop said the brakes had worn through the rim.

Seems hard to believe that hard rubber can wear thru aluminum.

Is that common ?

Rear, I'd say rare, but I've seen a number of rims where the metal is
down to coke can thickness and a circumferential crack developed.

So yes it does, but must have been high mileage.

On Friday, February 26, 2021 at 7:30:02 PM UTC-8, AK wrote:
Today while riding, my rear brakes locked up.

While investigating, the rear tire blew up causing part of the rim on one side to split off.

The tech at the shop said the brakes had worn through the rim.

Seems hard to believe that hard rubber can wear thru aluminum.

Is that common ?
It is the normal failure mode of aluminum rims. You are expected to check it regularly like you do for chain wear on cogs and rings. The easiest way is to hold a straight edge on the sidewall of the rim. If there is noticeable belly it is time to replace. Of course modern rims are being built to be lighter and so the sidewalls thinner and you should probably just keep an eye out for noticeable wear and if so pull the tire off and measure the sidewall width with a Vernier caliper.

On 2/27/2021 11:51 AM, Tosspot wrote:
On 27/02/2021 04:30, AK wrote:

Today while riding, my rear brakes locked up.

While investigating, the rear tire blew up causing part of the rim on
one side to split off.

The tech at the shop said the brakes had worn through the rim.

Seems hard to believe that hard rubber can wear thru aluminum.

Is that common ?

Rear, I'd say rare, but I've seen a number of rims where the metal is
down to coke can thickness and a circumferential crack developed.

So yes it does, but must have been high mileage.

Doesn't even have to be high mileage; miles in which one isn't braking
don't have any effect anyway.

I blew a rear rim from worn brake track. It was on my commuter bike.
Not that many miles, but all of them stop-and-go, and a great many of
them in the rain. Plus I was lazy and didn't clean the pads... ever.
So it was a rim-grinding trifecta. Stupid of me to not pay closer
attention, but there it is, or *was*.

Fortunately the blowout was at low speed shortly after a stoplight,
moving in a straight line. After that, I took care to check the brake
track and re-rim more regularly. I think I was getting about 5 years
out of a rim on that bike. Replaced it with a disk-brake bike.

Mark J.

On 2/27/2021 10:34 PM, Mark J. wrote:
On 2/27/2021 11:51 AM, Tosspot wrote:
On 27/02/2021 04:30, AK wrote:

Today while riding, my rear brakes locked up.

While investigating, the rear tire blew up causing part
of the rim on one side to split off.

The tech at the shop said the brakes had worn through the
rim.

Seems hard to believe that hard rubber can wear thru
aluminum.

Is that common ?

Rear, I'd say rare, but I've seen a number of rims where
the metal is down to coke can thickness and a
circumferential crack developed.

So yes it does, but must have been high mileage.

Doesn't even have to be high mileage; miles in which one
isn't braking don't have any effect anyway.

I blew a rear rim from worn brake track. It was on my
commuter bike. Not that many miles, but all of them
stop-and-go, and a great many of them in the rain. Plus I
was lazy and didn't clean the pads... ever. So it was a
rim-grinding trifecta. Stupid of me to not pay closer
attention, but there it is, or *was*.

Fortunately the blowout was at low speed shortly after a
stoplight, moving in a straight line. After that, I took
care to check the brake track and re-rim more regularly. I
think I was getting about 5 years out of a rim on that
bike. Replaced it with a disk-brake bike.

Mark J.

It's not mileage so much as braking frequency and filth.
Daily year-round commuting just grinds up pads and rims
whereas a cross country 3000 mile excursion not so much.

--
Andrew Muzi
www.yellowjersey.org/
Open every day since 1 April, 1971

On Sunday, February 28, 2021 at 8:13:03 AM UTC-8, AMuzi wrote:
On 2/27/2021 10:34 PM, Mark J. wrote:
On 2/27/2021 11:51 AM, Tosspot wrote:
On 27/02/2021 04:30, AK wrote:

Today while riding, my rear brakes locked up.

While investigating, the rear tire blew up causing part
of the rim on one side to split off.

The tech at the shop said the brakes had worn through the
rim.

Seems hard to believe that hard rubber can wear thru
aluminum.

Is that common ?

Rear, I'd say rare, but I've seen a number of rims where
the metal is down to coke can thickness and a
circumferential crack developed.

So yes it does, but must have been high mileage.

Doesn't even have to be high mileage; miles in which one
isn't braking don't have any effect anyway.

I blew a rear rim from worn brake track. It was on my
commuter bike. Not that many miles, but all of them
stop-and-go, and a great many of them in the rain. Plus I
was lazy and didn't clean the pads... ever. So it was a
rim-grinding trifecta. Stupid of me to not pay closer
attention, but there it is, or *was*.

Fortunately the blowout was at low speed shortly after a
stoplight, moving in a straight line. After that, I took
care to check the brake track and re-rim more regularly. I
think I was getting about 5 years out of a rim on that
bike. Replaced it with a disk-brake bike.

Mark J.
It's not mileage so much as braking frequency and filth.
Daily year-round commuting just grinds up pads and rims
whereas a cross country 3000 mile excursion not so much.

As I've mentioned, one of my work cohorts commuted (back when people left their homes for work) probably 20 miles a work day year round and would grind through rims about every two years. He is a heavy guy and rode a lot in the rain. He also switched to discs. I switched to discs long before him, but I never paid attention to how much life I got out of my rims -- which would wear thin and often die of other reasons like spoke hole cracks or whacking something. My cohort paid others to rebuild wheels for him, so he was much more attuned to how often he was replacing rims.

-- Jay Beattie.

On Sunday, February 28, 2021 at 2:40:08 PM UTC-8, jbeattie wrote:
On Sunday, February 28, 2021 at 8:13:03 AM UTC-8, AMuzi wrote:
On 2/27/2021 10:34 PM, Mark J. wrote:
On 2/27/2021 11:51 AM, Tosspot wrote:
On 27/02/2021 04:30, AK wrote:

Today while riding, my rear brakes locked up.

While investigating, the rear tire blew up causing part
of the rim on one side to split off.

The tech at the shop said the brakes had worn through the
rim.

Seems hard to believe that hard rubber can wear thru
aluminum.

Is that common ?

Rear, I'd say rare, but I've seen a number of rims where
the metal is down to coke can thickness and a
circumferential crack developed.

So yes it does, but must have been high mileage.

Doesn't even have to be high mileage; miles in which one
isn't braking don't have any effect anyway.

I blew a rear rim from worn brake track. It was on my
commuter bike. Not that many miles, but all of them
stop-and-go, and a great many of them in the rain. Plus I
was lazy and didn't clean the pads... ever. So it was a
rim-grinding trifecta. Stupid of me to not pay closer
attention, but there it is, or *was*.

Fortunately the blowout was at low speed shortly after a
stoplight, moving in a straight line. After that, I took
care to check the brake track and re-rim more regularly. I
think I was getting about 5 years out of a rim on that
bike. Replaced it with a disk-brake bike.

Mark J.
It's not mileage so much as braking frequency and filth.
Daily year-round commuting just grinds up pads and rims
whereas a cross country 3000 mile excursion not so much.
As I've mentioned, one of my work cohorts commuted (back when people left their homes for work) probably 20 miles a work day year round and would grind through rims about every two years. He is a heavy guy and rode a lot in the rain. He also switched to discs. I switched to discs long before him, but I never paid attention to how much life I got out of my rims -- which would wear thin and often die of other reasons like spoke hole cracks or whacking something. My cohort paid others to rebuild wheels for him, so he was much more attuned to how often he was replacing rims.

When I was riding about 10,000 miles a year I couldn't use those original Mavic rims because I would go through them in a year. Then they came out with the deeper thicker ones (MA-2's?).

On Sunday, February 28, 2021 at 10:13:03 AM UTC-6, AMuzi wrote:

It's not mileage so much as braking frequency and filth.
Daily year-round commuting just grinds up pads and rims
whereas a cross country 3000 mile excursion not so much.
--
Andrew Muzi
www.yellowjersey.org/
Open every day since 1 April, 1971
This has been my experience. My daily commuter has 20" wheels, and I was getting about 2,000 miles on a rear* rim before wear was apparent. Luckily, the wheel would start to "thump" during brake application, so I could see the problem coming. This problem was worse on the bike I use in the winter, until I replaced the rim brake with a "roller" brake. No rim failures since.

A good tool for measuring rim sidewall thickness is a "crown thickness gauge", also known as an "Iwanson gauge" (https://www.prestige-dental.co.uk/pr...ckness-gauge/). These are better at measuring the thickness of small areas, especially when there are interferences like the hooks on the inside of the rim than are vernier calipers. These are accurate to 0.1mm if they are well made, and aren't really expensive.
Most of my new rims are about 1.5mm thick, and when they get to be between 0.5 and 1.0mm they are getting ready to be replaced.

*It's always a rear rim. I've never worn out a front rim (though there is some concavity to the brake track). I think the front wheel kicks up dust or some other form of abrasive that lands on the rear rim and promotes more rapid wear.

On Sunday, February 28, 2021 at 4:37:46 PM UTC-8, Steve Weeks wrote:
On Sunday, February 28, 2021 at 10:13:03 AM UTC-6, AMuzi wrote:

It's not mileage so much as braking frequency and filth.
Daily year-round commuting just grinds up pads and rims
whereas a cross country 3000 mile excursion not so much.
--
Andrew Muzi
www.yellowjersey.org/
Open every day since 1 April, 1971
This has been my experience. My daily commuter has 20" wheels, and I was getting about 2,000 miles on a rear* rim before wear was apparent. Luckily, the wheel would start to "thump" during brake application, so I could see the problem coming. This problem was worse on the bike I use in the winter, until I replaced the rim brake with a "roller" brake. No rim failures since.

A good tool for measuring rim sidewall thickness is a "crown thickness gauge", also known as an "Iwanson gauge" (https://www.prestige-dental.co.uk/pr...ckness-gauge/). These are better at measuring the thickness of small areas, especially when there are interferences like the hooks on the inside of the rim than are vernier calipers. These are accurate to 0.1mm if they are well made, and aren't really expensive.
Most of my new rims are about 1.5mm thick, and when they get to be between 0.5 and 1.0mm they are getting ready to be replaced.

*It's always a rear rim. I've never worn out a front rim (though there is some concavity to the brake track). I think the front wheel kicks up dust or some other form of abrasive that lands on the rear rim and promotes more rapid wear.
That is an extremely odd looking tool but dental tools have to be capable of measuring to great accuracy.

On 2/28/2021 6:37 PM, Steve Weeks wrote:
On Sunday, February 28, 2021 at 10:13:03 AM UTC-6, AMuzi wrote:

It's not mileage so much as braking frequency and filth.
Daily year-round commuting just grinds up pads and rims
whereas a cross country 3000 mile excursion not so much.

This has been my experience. My daily commuter has 20" wheels, and I was getting about 2,000 miles on a rear* rim before wear was apparent. Luckily, the wheel would start to "thump" during brake application, so I could see the problem coming. This problem was worse on the bike I use in the winter, until I replaced the rim brake with a "roller" brake. No rim failures since.

A good tool for measuring rim sidewall thickness is a "crown thickness gauge", also known as an "Iwanson gauge" (https://www.prestige-dental.co.uk/pr...ckness-gauge/). These are better at measuring the thickness of small areas, especially when there are interferences like the hooks on the inside of the rim than are vernier calipers. These are accurate to 0.1mm if they are well made, and aren't really expensive.
Most of my new rims are about 1.5mm thick, and when they get to be between 0.5 and 1.0mm they are getting ready to be replaced.

*It's always a rear rim. I've never worn out a front rim (though there is some concavity to the brake track). I think the front wheel kicks up dust or some other form of abrasive that lands on the rear rim and promotes more rapid wear.


Good analysis.
I think that's exactly why front rim sidewall failure is
vanishingly rare despite theoretically more braking force
and usually faster front pad wear.

--
Andrew Muzi
www.yellowjersey.org/
Open every day since 1 April, 1971

On 2/28/2021 8:10 PM, AMuzi wrote:
On 2/28/2021 6:37 PM, Steve Weeks wrote:
On Sunday, February 28, 2021 at 10:13:03 AM UTC-6, AMuzi wrote:

It's not mileage so much as braking frequency and filth.
Daily year-round commuting just grinds up pads and rims
whereas a cross country 3000 mile excursion not so much.

This has been my experience. My daily commuter has 20" wheels, and I
was getting about 2,000 miles on a rear* rim before wear was apparent.
Luckily, the wheel would start to "thump" during brake application, so
I could see the problem coming. This problem was worse on the bike I
use in the winter, until I replaced the rim brake with a "roller"
brake. No rim failures since.

A good tool for measuring rim sidewall thickness is a "crown thickness
gauge", also known as an "Iwanson gauge"
(https://www.prestige-dental.co.uk/pr...ckness-gauge/).
These are better at measuring the thickness of small areas, especially
when there are interferences like the hooks on the inside of the rim
than are vernier calipers. These are accurate to 0.1mm if they are
well made, and aren't really expensive.
Most of my new rims are about 1.5mm thick, and when they get to be
between 0.5 and 1.0mm they are getting ready to be replaced.

*It's always a rear rim. I've never worn out a front rim (though there
is some concavity to the brake track). I think the front wheel kicks
up dust or some other form of abrasive that lands on the rear rim and
promotes more rapid wear.


Good analysis.
I think that's exactly why front rim sidewall failure is vanishingly
rare despite theoretically more braking force and usually faster front
pad wear.

Sounds like yet another good reason to run fenders and a front mudflap!


--
- Frank Krygowski