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PostPosted: Fri Dec 08, 2017 6:54 pm 
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I will admit certain aspects of the test visually came across as a bit of PR but it's nice to see them making the effort. Everyone has to do a bit of marketing in the end to some degree and I like seeing companies invest in safety tests.

But I do agree with James in the CT article in regards to the bigger issue being that this is still an issue.

I do wonder if when disc become the majority in production (if\when) for manufacturers if we will ever see a solution to this problem or if it will as they said simply dip by the wayside.

Standardized testing would be great but I don't foresee that happening.

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PostPosted: Fri Dec 08, 2017 10:11 pm 
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The test is interesting because it shows people that carbon clinchers are a half baked product. If you use them under the "wrong" conditions you melt the brake track resin and the tire pressure pushes on and ruptures the brake track.

I'm a little skeptical that Alto has a secret resin that Zipp, Enve or Mavic cannot come up with. Also, in the test, the temperature on the Alto never rose which leads me to believe that less friction and thus less braking force was being generated. Or, assuming that the same braking force was generated how can the Alto rim shed the heat and maintain a lower temperature indefinitely?

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Posted: Fri Dec 08, 2017 10:11 pm 


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PostPosted: Fri Dec 08, 2017 11:16 pm 
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I see a few issues. The pad thing yes and no. ANY braking will generate heat. The heat is a byproduct of changing the energy from speed to thermal energy. Remember that energy cannot be created or destroyed only transferred between forms. That said alto's response that any different pad would just delay but not avoid failure is strange as they specify in a cyclingtips review of their CC40 rims that ONLY blackprince can be used.

Second their wheel seems to run the fastest - it sits at 20.5 mph whilst the others hover at 19.5ish on average. As others have suggested at a constant motor power this can only be due to reduced friction at the brake pad rim bed zone.

The test should have a variable brake lever pull to achieve the same speed at a given motor output. I think this is more important than brake pad used.
The test is useful as it shows the failure mode of the rim. Some would be saveable in a blowout situation. The roval and boyd failures would lead to a crash.

Re the result shows carbon clinchers are not safe. I don't see that this represents real world usage at all. I use carbon clinchers for everything.( I also have a set of tubs) There are very few descents I have ridden where I have had concern for the brake track temperature. As far as people saying this proves that they are not fit for being on the road where such conditions MAY occur, then I would say anybody that has ever hit a pothole and flatted has chosen equipment not fit for purpose as pothole related blowouts are FAR more likely than rim delaminations unless your daily commute involves descending mortirolo in traffic.

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PostPosted: Fri Dec 08, 2017 11:42 pm 
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NiFTY wrote:
Re the result shows carbon clinchers are not safe. I don't see that this represents real world usage at all. I use carbon clinchers for everything.( I also have a set of tubs) There are very few descents I have ridden where I have had concern for the brake track temperature. As far as people saying this proves that they are not fit for being on the road where such conditions MAY occur, then I would say anybody that has ever hit a pothole and flatted has chosen equipment not fit for purpose as pothole related blowouts are FAR more likely than rim delaminations unless your daily commute involves descending mortirolo in traffic.


A flat from a pothole (especially since I run tubeless and the bead wouldn't roll off) is unlikely to send me careening off the side of a mountain or put you on the ground instantly like the Boyd and Roval wheel explosions would have. Flats are unfortunate. Damaged rim edges are unfortunate. Complete and utter rim failure is way more than that.

I've already noted the Knight Composites wheel a friend of a friend blew up in much the same way at Phil's Fondo.

Here's the photo he sent me:

Image

The problem is very real, and we shouldn't diminish that just because we suspect some of the test parameters were cherry-picked.


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PostPosted: Sat Dec 09, 2017 1:19 am 
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https://knightcomposites.com/testing/

they have section on how the test rim failure. ironic part the youtube video is no longer available.

these clowns charge primo dollars for crap product. marketing. amazing cycling business

What:
Brakes are repeatedly applied and released to test the brake track durability and heat resistance.

How:
A rim is placed in the test rig and with a load of 100kg. It is then rotated constantly at 12.5kph, while the brakes are engaged and disengaged at a set pressure every 3 seconds. Rims should endure 3000 cycles of braking with no sign of failure to meet industry standards.

Why:
This tests how well the rim can withstand the heat generated from braking on the carbon track.

https://www.youtube.com/watch?v=T3Fu53u ... e=youtu.be

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PostPosted: Sat Dec 09, 2017 2:25 am 
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Flawed or not, an interesting video.

In all cases rotational energy is being converted into heat via friction by the pad (does the pad really matter in this case). A superior rim can either withstand higher temperatures longer, or dissipate the heat faster so higher temperatures are not achieved.

Hard to understand how different rims would have significantly different heat dissipation characteristics (similar areas and U values) so if one rim runs at a lower temp then it must be because the friction is lower. And if the temp is lower then its not really an apples to apples test. You would expect at lower temps the rim to last longer.


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PostPosted: Sat Dec 09, 2017 2:38 am 
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apctjb wrote:
Flawed or not, an interesting video.

In all cases rotational energy is being converted into heat via friction by the pad (does the pad really matter in this case). A superior rim can either withstand higher temperatures longer, or dissipate the heat faster so higher temperatures are not achieved.

Hard to understand how different rims would have significantly different heat dissipation characteristics (similar areas and U values) so if one rim runs at a lower temp then it must be because the friction is lower. And if the temp is lower then its not really an apples to apples test. You would expect at lower temps the rim to last longer.

yeah. As in not stopping but intact. Over the guardrail either way...


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PostPosted: Sat Dec 09, 2017 3:22 am 
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Just because there are design parameters of a product and it will fail outside of those parameters doesn't mean the product is bad design. Try doing this with alloy clinchers and watch tires blow off or with disc brakes and the hydraulic fluid will begin boiling. All of that is possibly just as bad to the rider descending.

I think the video is interesting and probably flawed but some things can probably be inferred from it. One of which is that I might not be shopping for knights wheels any time soon.

If they had used manufactures specified pads, couldn't they do a few short tests to determine the appropriate force and then normalized it to some target watts/second absorbed target?

I'd also love to see what it takes to cause deformation in a tubular rim. My guess is that the wheel would have to be loaded otherwise there probably wouldn't be sufficient forces on the rim to take advantage of any weakening of the composites.

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PostPosted: Sat Dec 09, 2017 4:19 am 
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RyanH wrote:
Just because there are design parameters of a product and it will fail outside of those parameters doesn't mean the product is bad design. Try doing this with alloy clinchers and watch tires blow off or with disc brakes and the hydraulic fluid will begin boiling. All of that is possibly just as bad to the rider descending.


With disc brakes you're going to experience gradual brake fade before the hydraulic fluid starts boiling. That should be a good indication that you should stop and let the system cool down a bit.


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PostPosted: Sat Dec 09, 2017 10:33 pm 
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RyanH wrote:

I'd also love to see what it takes to cause deformation in a tubular rim. My guess is that the wheel would have to be loaded otherwise there probably wouldn't be sufficient forces on the rim to take advantage of any weakening of the composites.

There's a comment on the Cyclingtips article on this from a guy that melted a tubular LEW on Sonora. Granted, that's old tech, but he made it down after allowing it to cool. Had a pretty good thump though.

I doubt I would do any type of alpine work with a carbon clincher. Tubular? Yeah probably, but I'd likely stop multiple times down to allow full cooling. Unless the road is closed, too much braking going on. Al33's or something probably worth the weight penalty in these situations. Eastern US climbs are a different story, except Mt. Mitchell and the like.


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PostPosted: Sun Dec 10, 2017 9:41 am 
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Been riding in the alps with carbon clinchers for years now, never a problem.


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PostPosted: Mon Dec 11, 2017 3:59 am 
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Marin wrote:
Been riding in the alps with carbon clinchers for years now, never a problem.


That's great, but some people do have problems, especially less confident cyclists who drag their brakes a lot.


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PostPosted: Mon Dec 11, 2017 11:06 am 
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TobinHatesYou wrote:
Marin wrote:
Been riding in the alps with carbon clinchers for years now, never a problem.


That's great, but some people do have problems, especially less confident cyclists who drag their brakes a lot.


Some people who can't corner also crash, not the bikes fault. Its like blaming standard chainrings because a fat guy can't ride then up hill.

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PostPosted: Mon Dec 11, 2017 12:11 pm 
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Seeing the rims explode in the test is one thing, but when you see a picture of a real world rim in the state Tobin posted is pretty scary.

They need to come with obvious warnings if they can't handle prolonged braking without that happening to them.


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PostPosted: Mon Dec 11, 2017 1:44 pm 
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NiFTY wrote:
TobinHatesYou wrote:
Marin wrote:
Been riding in the alps with carbon clinchers for years now, never a problem.


That's great, but some people do have problems, especially less confident cyclists who drag their brakes a lot.


Some people who can't corner also crash, not the bikes fault. Its like blaming standard chainrings because a fat guy can't ride then up hill.

1) confident or not you have cases where you are forced to keep braking... just yesterday, the traffic forced me to brake almost continuously for 6km.
2) disagree with the crash example. People do not blame their bike when they crash in a corner and if you are not a good downhiller (or don't want to risk or multiple other reasons) you have the option to go slower... then brake, but if the rim doesn't allow it then yes I would blame the material.


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Posted: Mon Dec 11, 2017 1:44 pm 


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