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Replace Mavic MA40 Rim with... ?



 
 
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  #11  
Old September 28th 19, 02:05 PM posted to rec.bicycles.tech
AMuzi
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Posts: 13,447
Default Replace Mavic MA40 Rim with... ?

On 9/28/2019 7:51 AM, wrote:
Thank you for the further input, jbeattie, John, David, AMuzi and Tosspot. I squeezed the sides of the braking surface, and the rim seems solid.

I was going to buy a whole new pre-built wheel, but then, after a long day of other activities and needing some athleticism and beauty, decided to take one last ride on my Vitus. Both tire pressures felt a bit low, so I pumped them up to my usual 110 psi. The noise went away!

My tires are Schwalbe Marathon Plus. (Where I am in the Southwest, there are goatheads galore. I have not had a flat since installing the tires a couple of years ago.) I am wondering if the tires had something to do with the noise.


I have no idea about your noise.
But if I recall, your earlier concern was a bearing problem,
yes?

Slip the wheel out of the bike and turn the axle in your
fingers. Any roughness? Any end play? If so, clean and
evaluate; rebuild or replace. If not, oil the cam of your QR
and lock the wheel properly in the bike.

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


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  #12  
Old September 28th 19, 03:06 PM posted to rec.bicycles.tech
Frank Krygowski[_2_]
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Default Replace Mavic MA40 Rim with... ?

On Saturday, September 28, 2019 at 8:51:31 AM UTC-4, wrote:
Thank you for the further input, jbeattie, John, David, AMuzi and Tosspot. I squeezed the sides of the braking surface, and the rim seems solid.


Is there a rule of thumb for minimum safe rim thickness at the braking surfaces?

- Frank Krygowski
  #13  
Old September 28th 19, 05:00 PM posted to rec.bicycles.tech
AMuzi
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Posts: 13,447
Default Replace Mavic MA40 Rim with... ?

On 9/28/2019 9:06 AM, Frank Krygowski wrote:
On Saturday, September 28, 2019 at 8:51:31 AM UTC-4, wrote:
Thank you for the further input, jbeattie, John, David, AMuzi and Tosspot. I squeezed the sides of the braking surface, and the rim seems solid.


Is there a rule of thumb for minimum safe rim thickness at the braking surfaces?

- Frank Krygowski

Yes.
Go this far:
http://www.yellowjersey.org/photosfr...st/wornrim.jpg

and then reverse the wear a little.

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


  #15  
Old September 29th 19, 02:43 AM posted to rec.bicycles.tech
Steve Weeks
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Default Replace Mavic MA40 Rim with... ?

On Saturday, September 28, 2019 at 9:06:57 AM UTC-5, Frank Krygowski wrote:

Is there a rule of thumb for minimum safe rim thickness at the braking surfaces?


I've worn a couple rims to the point where they have begun to show cracks along the braking surfaces. The brake on the affected wheel would "pulse" slightly because of the wide spot. The brake surface was between 0.5 and 1.0mm thick. Most of the new rims I've measured have 1.4 to 1.6mm of brake surface thickness. So I'd say when the thickness reaches around 1.0mm it would be time to start looking for a brake pulsation and planning a rim replacement at a convenient future time.
  #16  
Old September 29th 19, 03:29 PM posted to rec.bicycles.tech
Frank Krygowski[_2_]
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Default Replace Mavic MA40 Rim with... ?

On Saturday, September 28, 2019 at 9:43:30 PM UTC-4, Steve Weeks wrote:
On Saturday, September 28, 2019 at 9:06:57 AM UTC-5, Frank Krygowski wrote:

Is there a rule of thumb for minimum safe rim thickness at the braking surfaces?


I've worn a couple rims to the point where they have begun to show cracks along the braking surfaces. The brake on the affected wheel would "pulse" slightly because of the wide spot. The brake surface was between 0.5 and 1.0mm thick. Most of the new rims I've measured have 1.4 to 1.6mm of brake surface thickness. So I'd say when the thickness reaches around 1.0mm it would be time to start looking for a brake pulsation and planning a rim replacement at a convenient future time.


1 mm sounds pretty practical to me.

I've never ground a rim down to failure, but I think I'm pretty easy on brakes.
Unlike Jay, I only rarely rode to or from work in the rain. I was comfortable
coasting at 30 mph on the way to work, since my routes were mostly low traffic
roads. And when biking (as when driving) I tend to watch far ahead for potential
conflicts or events.

- Frank Krygowski
  #17  
Old September 29th 19, 07:37 PM posted to rec.bicycles.tech
Ned Mantei[_2_]
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Default Replace Mavic MA40 Rim with... ?

On 28-09-19 16:06, Frank Krygowski wrote:
On Saturday, September 28, 2019 at 8:51:31 AM UTC-4, wrote:
Thank you for the further input, jbeattie, John, David, AMuzi and Tosspot. I squeezed the sides of the braking surface, and the rim seems solid.


Is there a rule of thumb for minimum safe rim thickness at the braking surfaces?

- Frank Krygowski


Some (many? most?) rims have wear indicators. At least for Mavic XC717
and X719 there are/were tiny holes going partway into the rim. The idea
is that the rim should be replaced when the holes are no longer visible.
However, more often I have replaced the rim because the brake is
grabbing at one spot, which could be because the rim is getting wider
there and might fail. After once replacing a rim for this reason I took
the old rim to my LBS to ask whether they would have done something
similar. They broke the rim into pieces by putting it between the jaws
of a vise and pushing back. One part of the rim wall at a break was only
about 0.7 or 0.8 mm thick, dangerously thin. However, just now it
occurred to me that this could have been because the rim wall
"stretched" as it was being broken apart, so I'm not sure that this was
a proper measurement. Clearly I should break a brand new rim as a
control, but I'll pass on this.

My older bikes have 26" wheels, and it's becoming difficult to
impossible to find rims with the effective rim diameter that will fit
the old hubs and spokes. For two bikes, 13 and 16 years old, it would
have been time for rim #5 on the back wheel. Replacing both the spokes
and rims was more than I wanted to deal with, and the hubs were anyhow
old, so I gave up and bought complete new wheels.

Ned
  #18  
Old September 29th 19, 11:00 PM posted to rec.bicycles.tech
Sir Ridesalot
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Posts: 5,270
Default Replace Mavic MA40 Rim with... ?

On Saturday, 28 September 2019 12:00:41 UTC-4, AMuzi wrote:
On 9/28/2019 9:06 AM, Frank Krygowski wrote:
On Saturday, September 28, 2019 at 8:51:31 AM UTC-4, wrote:
Thank you for the further input, jbeattie, John, David, AMuzi and Tosspot. I squeezed the sides of the braking surface, and the rim seems solid.


Is there a rule of thumb for minimum safe rim thickness at the braking surfaces?

- Frank Krygowski

Yes.
Go this far:
http://www.yellowjersey.org/photosfr...st/wornrim.jpg

and then reverse the wear a little.

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


That looks like the used Matrix rim I had that recently failed!

Cheers
  #19  
Old September 30th 19, 04:06 AM posted to rec.bicycles.tech
Frank Krygowski[_2_]
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Posts: 7,511
Default Replace Mavic MA40 Rim with... ?

On Sunday, September 29, 2019 at 2:37:44 PM UTC-4, Ned Mantei wrote:

Some (many? most?) rims have wear indicators. At least for Mavic XC717
and X719 there are/were tiny holes going partway into the rim. The idea
is that the rim should be replaced when the holes are no longer visible.


None of my rims have those. If I had one around, I'd mike the thickness from
the bottom of the wear indicator to the inside edge of the rim. That should be the assumed minimum safe thickness.

- Frank Krygowski
  #20  
Old September 30th 19, 05:19 AM posted to rec.bicycles.tech
Sir Ridesalot
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Posts: 5,270
Default Replace Mavic MA40 Rim with... ?

On Sunday, 29 September 2019 23:06:52 UTC-4, Frank Krygowski wrote:
On Sunday, September 29, 2019 at 2:37:44 PM UTC-4, Ned Mantei wrote:

Some (many? most?) rims have wear indicators. At least for Mavic XC717
and X719 there are/were tiny holes going partway into the rim. The idea
is that the rim should be replaced when the holes are no longer visible.


None of my rims have those. If I had one around, I'd mike the thickness from
the bottom of the wear indicator to the inside edge of the rim. That should be the assumed minimum safe thickness.

- Frank Krygowski


Then again, that wear indicator, or at least the ones I've seen, are akin to a deep gouge and I wonder if they in themselves don't become a stress riser as the rim wears down towards the bottom of the groove. What's your guess on that?

Cheers
 




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