Specific heat absorption capacity of disc brakes

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eCue   10 kW

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Re: Specific heat absorption capacity of disc brakes

Post by eCue » Feb 03 2018 3:45am

The TRP Spire disc is working well in every respect. Solid feeling smooth without vibration quiet make that dead quiet and with good modulation.
Currently waiting for a bottom bracket cable guide to get the rear roller brake operating. Ive been using front disk exclusively these last few days. At first tried the brake lever in roller brake mode for a day.
It was spongy and required too much force to stop. Impossible to lock up in error and had a very long braking distance. Rather dangerous
V-brake mode felt so much better having both a sharp pull when needed and nice modulation. I have not had a error lock up and dont think I will. The Organic pads are silent and smoother then smooth , I can see why they are suggested up front.
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Re: Specific heat absorption capacity of disc brakes

Post by Chalo » Feb 03 2018 2:31pm

eCue wrote:
Feb 03 2018 3:45am
At first tried the brake lever in roller brake mode for a day.
It was spongy and required too much force to stop. Impossible to lock up in error and had a very long braking distance. Rather dangerous
V-brake mode felt so much better having both a sharp pull when needed and nice modulation.
My favorite levers to use with drums and roller brakes have been adjustable gain linear pull levers, like Avid Speed Dial or Dia-Compe PC-7 EXA. However, I feel that long blades are an advantage in this application, and linear pull levers generally have short blades.

So-called "compressionless" brake cable housing is really good at improving lever feel and brake response with drum or roller brakes. I didn't believe it until I tried it.
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Re: Specific heat absorption capacity of disc brakes

Post by amberwolf » Feb 04 2018 2:44am

Chalo wrote:
Feb 03 2018 2:31pm
So-called "compressionless" brake cable housing is really good at improving lever feel and brake response with drum or roller brakes.
Is that the kind with the full-housing-length "wires" paralleled around the circumference of the housing? (rather than the spiral-wrapped type)

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Re: Specific heat absorption capacity of disc brakes

Post by Chalo » Feb 04 2018 10:04am

amberwolf wrote:
Feb 04 2018 2:44am
Chalo wrote:
Feb 03 2018 2:31pm
So-called "compressionless" brake cable housing is really good at improving lever feel and brake response with drum or roller brakes.
Is that the kind with the full-housing-length "wires" paralleled around the circumference of the housing? (rather than the spiral-wrapped type)
Yes, but it differs from index shift housing in that the parallel wires are contained in a snug Kevlar jacket to keep the housing from bursting under high compressive load. Here's the kind I use.

I had encountered long lay cable housing before that promised compatibility with both brakes and shifters; it was marketed by Odyssey. But that stuff definitely wasn't stiffer in compression than good quality Bowden cable housing.
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Re: Specific heat absorption capacity of disc brakes

Post by Raisedeyebrows » Feb 05 2018 12:42am

I have the Jagwire housing on my cargo bike with BB7's, the stuff is worth the money, really stiffened up the braking response.
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Re: Specific heat absorption capacity of disc brakes

Post by Chalo » Feb 07 2018 8:03pm

Prototyped a new fork today for a super- heavyweight pedicab. We opted for dual 203mm discs, which was the main reason we had to make our own fork.
rps20180207_173222.jpg
rps20180207_173222.jpg (78.53 KiB) Viewed 1352 times
That's a 29x2.1" tire on a 42mm wide rim.
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Re: Specific heat absorption capacity of disc brakes

Post by speedmd » Feb 07 2018 9:35pm

Nice! Like the look of the rotors mounted backwards.

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Re: Specific heat absorption capacity of disc brakes

Post by Chalo » Feb 07 2018 9:39pm

speedmd wrote:
Feb 07 2018 9:35pm
Nice! Like the look of the rotors mounted backwards.
Yep. Good thing there are no calipers on it yet.

I'm on the lookout for reasonably priced 8" rotors with a non-directional pattern to prevent the inevitable reverse installation of the symmetrical wheel by end users. Any ideas?
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Re: Specific heat absorption capacity of disc brakes

Post by speedmd » Feb 07 2018 9:47pm

Brakco? Closer to a bi directional design. Float points and outer slots not.
https://www.ebay.com/i/282773086090?chn ... 2056669164
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Re: Specific heat absorption capacity of disc brakes

Post by speedmd » Feb 07 2018 10:25pm

The Ashima looks to be more symmetrical at the float points.
https://www.ebay.com/itm/Ashima-Flotor- ... SwEetWAvqN
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Re: Specific heat absorption capacity of disc brakes

Post by speedmd » Feb 08 2018 9:57am

Origin looks to be fully symmetrical, but possibly some cbore at the mounting screws. Not sure outer slots on the lower cost option would be a issue. KCNC also with a nice lightweight design. https://www.ebay.com/itm/Origin-8-Speed ... SwVqlaHClC
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Re: Specific heat absorption capacity of disc brakes

Post by Chalo » Feb 08 2018 11:53am

Thanks for finding these.
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Re: Specific heat absorption capacity of disc brakes

Post by speedmd » Feb 08 2018 12:25pm

Chalo wrote:
Feb 08 2018 11:53am
Thanks for finding these.
No problem. Like the idea of dual rotors, have been playing with the idea and glad you posted as we have many near moto requirements here that can test these lightweights out for suitability. Even if you need to get some outer rings water jet'd out a bit more heavy duty, the center hub may become a standard for most here on ES.

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Re: Specific heat absorption capacity of disc brakes

Post by Lebowski » Mar 09 2018 3:16am

Lebowski wrote:
Dec 14 2017 7:56am
I agree with Chalo about rim brakes... I mean disc brakes are getting larger and larger diameter, only a few more years till the disks are as large as the rims.... at which point everyone will realise rim brakes are basically disc brakes with the biggest disk possible.
:shock: just went through the rim...
DSC02093-800x800.jpg
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Re: Specific heat absorption capacity of disc brakes

Post by justin_le » Mar 09 2018 3:50am

Lebowski wrote:
Mar 09 2018 3:16am
:shock: just went through the rim...
Ha ha, funny timing. I've done that a few times myself and witnessed it countless times on customer ebikes.
There's a reason for disk brakes. But the ultimate solution for ebikes, of course, is GOOD REGEN!!!!
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Re: Specific heat absorption capacity of disc brakes

Post by Lebowski » Mar 09 2018 5:26am

I have good regen :mrgreen: just not on this bike.

This one is a non-ebike which I use 2-3 times a week to climb the local 350 m high hills. Then on the descent I am lightly on the brakes to keep speed around 40 kmh. I am happy that I didnt do a strong brake action, pushing through the rim locking the wheel. I think the wheel has around 20000 km on it...

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Re: Specific heat absorption capacity of disc brakes

Post by Chalo » Mar 09 2018 1:43pm

Lebowski wrote:
Mar 09 2018 3:16am
Lebowski wrote:
Dec 14 2017 7:56am
I agree with Chalo about rim brakes... I mean disc brakes are getting larger and larger diameter, only a few more years till the disks are as large as the rims.... at which point everyone will realise rim brakes are basically disc brakes with the biggest disk possible.
:shock: just went through the rim...
DSC02093-800x800.jpg
When I lived in Seattle, it seemed like year-round commuters would grind through their rims every year or two. Here in Austin, it only rarely happens, mostly to MTBers who intentionally ride in mud. Seattle's dirt is more abrasive, and it's wet and gritty most of the time.

I can say that in more than 200,000 miles of cycling, mostly with rim brakes, I've never worn out a rim sidewall.
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Re: Specific heat absorption capacity of disc brakes

Post by Voltron » Mar 09 2018 2:48pm

From a recent wheel that came in... he was a Canadian transplant and running high psi tires, which seems to be a commonality in the rim failures I've seen.
rimcrack.jpg
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rimcrack2.jpg
rimcrack2.jpg (46.55 KiB) Viewed 1162 times

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Re: Specific heat absorption capacity of disc brakes

Post by Chalo » Mar 09 2018 3:18pm

I did that in the distant past, running 140psi in 700x28 tires.

I don't exceed pressure ratings anymore; I just use tires that are big enough for the job.
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Re: Specific heat absorption capacity of disc brakes

Post by liveforphysics » Mar 09 2018 3:32pm

Odd folks think your rotors are mounted backwards. As a man who has overheated and wadded up a half dozen bicycle brake rotors into a hot mess of steel, I found mounting them they way you did so it pulls on the rotor spokes vs pushing on the rotor spokes enabled them to survive much longer at extreme temps.


Chalo wrote:
Feb 07 2018 8:03pm
Prototyped a new fork today for a super- heavyweight pedicab. We opted for dual 203mm discs, which was the main reason we had to make our own fork.

rps20180207_173222.jpg

That's a 29x2.1" tire on a 42mm wide rim.
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Re: Specific heat absorption capacity of disc brakes

Post by DanGT86 » Mar 09 2018 4:15pm

Iv'e also always thought rotors should be mounted that way as well. Seems like in the case of a catastrophic rotor failure you would want the "spokes to fold away to a smaller radius rather than growing to a larger radius and stabbing everything. I guess its probably silly to try and apply logic to such a chaotic event.

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Re: Specific heat absorption capacity of disc brakes

Post by Chalo » Mar 09 2018 4:24pm

liveforphysics wrote:
Mar 09 2018 3:32pm
Odd folks think your rotors are mounted backwards. As a man who has overheated and wadded up a half dozen bicycle brake rotors into a hot mess of steel, I found mounting them they way you did so it pulls on the rotor spokes vs pushing on the rotor spokes enabled them to survive much longer at extreme temps.
In the picture, they are backwards relative to their directional markings.

I think the idea is that leading spokes exert an expanding force on the outer ring of the rotor, which helps keep it straight by means of hoop tension. Trailing spokes contract against the outer ring, promoting buckling. I don't know how much of this is founded in test results.

The first disc brakes I owned in the early '90s were Mountain Cycle Pro-Stop 9" full floating cable-hydraulic brakes with hard anodized aluminum rotors. They were labeled specifically to have trailing spokes when mounted, contrary to common practice today.

I figure I'll mount them the way the manufacturer suggests, all the while wondering why more disc rotors don't use a non-directional pattern.
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Re: Specific heat absorption capacity of disc brakes

Post by speedmd » Mar 09 2018 5:42pm

liveforphysics wrote:
Mar 09 2018 3:32pm
Odd folks think your rotors are mounted backwards. As a man who has overheated and wadded up a half dozen bicycle brake rotors into a hot mess of steel, I found mounting them they way you did so it pulls on the rotor spokes vs pushing on the rotor spokes enabled them to survive much longer at extreme temps.
[/quote]

I have used them both ways for a bit also. Never had a fail. Then I started seeing photos of the fails.
Image

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Re: Specific heat absorption capacity of disc brakes

Post by DanGT86 » Mar 10 2018 12:33am

Wow. I'm not an engineer but as a machinist I dont like anything about that rotor design. In my experience with steel you typically want to avoid sharp corners and avoid thin sections that concentrate heat/stress. That rotor looks like the worst possible design for the heat and loads it would be under. Just eyballing it though.

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Re: Specific heat absorption capacity of disc brakes

Post by liveforphysics » Mar 10 2018 7:09pm

Buckling the spokes from compression in a rotor happens way easier than pulling on them until tinsel strength failure.

You really want some offset in the spokes vs being radially arrayed, but just like in a bicycle wheel you want to be pulling on the spokes and with a hub exit offset.

Most bicycle brake rotors I've seen looked like they had artists make the designs to look flashy rather than doing a mechanical stress optimization.
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