Specific heat absorption capacity of disc brakes

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DanGT86
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Re: Specific heat absorption capacity of disc brakes

Post by DanGT86 » Dec 13, 2017 10:58 pm

Over the summer I was racing my ebike on a kart track and doing repeated hard decelerations from 45 down to 10mph. When I say hard decel I mean as hard as I could possibly brake and stay on the bike. I was butt off the seat in a crouch so low that I actually sat on the rear 24" tire a few times and the brakes were still effective enough to lift the rear wheel off the ground. The bike with me and gear was around 275lbs. Im running 10 year old avid Juicy 7 brakes up front and a junk hayes mechanical GX2 caliper in the rear with DH pads on 203mm standard rotors. Nothing fancy like an aluminum spider or sandwich vented disk just regular solid disk rotors. I know its not the most scientific data but anecdotally I can say that the brakes under full torture mode like this did have some fade but could still provide more grab than the tires or the geometry of the bike could handle. I think you would be skidding or going over the handlebars before you would ever be limited by brake fade with any 203mm setup. The fade is apparent but far from failure condition.

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Re: Specific heat absorption capacity of disc brakes

Post by eCue » Dec 14, 2017 12:21 am

The cart track sounds like a blast thats a fair amount of weight your stopping on the fly I have my eye on BB7's as I want stay with mechanical brakes this build just for roadside maintenance ease.

I have a set of XT hydraulic discs destined for a different bike the current ebike build is a 90's throw back build that does not have rear disc tabs. Its rear wheel has a roller brake mount so I'll go that way.

Just picked up this model on ebay for $40 with shipping

SHIMANO Roller Brake BR-IM55-R INTER M Brake NEXUS Rear Wheel

Image

for hubs with rollerbrake
Version: rear wheel high braking force
Cooling disk 140 mm
Weight: approx. 650 g
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Chalo
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Re: Specific heat absorption capacity of disc brakes

Post by Chalo » Dec 14, 2017 2:23 am

Cool. If you don't like it, don't give up on roller brakes. Just try one of the bigger models.
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Re: Specific heat absorption capacity of disc brakes

Post by Epyon » Dec 14, 2017 3:41 am

eCue wrote:
Dec 14, 2017 12:21 am
The cart track sounds like a blast thats a fair amount of weight your stopping on the fly I have my eye on BB7's as I want stay with mechanical brakes this build just for roadside maintenance ease.
Look into TRP Spykes. Leaps and bounds above the BB7s. You can probably find them for around $50 (per caliper). Then you'll need a lever. Avid Speed Dial 7s are great. Or if you have older V-brake ratio levers on hand, you could run TRP Spyres.

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Re: Specific heat absorption capacity of disc brakes

Post by Lebowski » Dec 14, 2017 7:56 am

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.

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Re: Specific heat absorption capacity of disc brakes

Post by Buk___ » Dec 14, 2017 8:38 am

Lebowski wrote:
Dec 14, 2017 7:56 am
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.
I'd still rather spend £6 on a disk and undo & do up 6 screws, that £30 on a rim, £3 on a tape, £25 on a set of spokes and 3 or 4 hours re-lacing.

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Re: Specific heat absorption capacity of disc brakes

Post by eCue » Dec 14, 2017 9:59 am

Chalo wrote:
Dec 14, 2017 2:23 am
Cool. If you don't like it, don't give up on roller brakes. Just try one of the bigger models.
This one is a models with a lager brake and it has a @ 140mm cooling disc its no slouch in the cooling department. Its in the same family as the 80 and 81 they share the same instruction set.
Its mot the best but its not a bad one
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Re: Specific heat absorption capacity of disc brakes

Post by eCue » Dec 14, 2017 10:48 am

Epyon wrote:
Dec 14, 2017 3:41 am
eCue wrote:
Dec 14, 2017 12:21 am
The cart track sounds like a blast thats a fair amount of weight your stopping on the fly I have my eye on BB7's as I want stay with mechanical brakes this build just for roadside maintenance ease.
Look into TRP Spykes. Leaps and bounds above the BB7s. You can probably find them for around $50 (per caliper). Then you'll need a lever. Avid Speed Dial 7s are great. Or if you have older V-brake ratio levers on hand, you could run TRP Spyres.
The plot thickens

Was going to use mechanical xtr levers until i bought the Roller brake they need a different pull lever so i need to upgrade / downgrade the levers to RB compatible. Pee me off as the money adds ups fast. Now I need levers ( they have a switch for v-brake or RB ) and a mech disc brake. With such a strong review in the TRP's favor I will try to find a TRP caliper within my price range
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Re: Specific heat absorption capacity of disc brakes

Post by Epyon » Dec 14, 2017 11:34 am

eCue wrote:
Dec 14, 2017 10:48 am
The plot thickens

Was going to use mechanical xtr levers until i bought the Roller brake they need a different pull lever so i need to upgrade / downgrade the levers to RB compatible. Pee me off as the money adds ups fast. Now I need levers ( they have a switch for v-brake or RB ) and a mech disc brake. With such a strong review in the TRP's favor I will try to find a TRP caliper within my price range
The Avid Speed Dial 7 levers are adjustable, not sure on the ratio range but I know they can be successfully used with v-brakes too. I know nothing about roller brakes and what they require.

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Re: Specific heat absorption capacity of disc brakes

Post by eCue » Dec 14, 2017 7:33 pm

They were selling the TRP Spyre with 160mm Rotor for $50 on eBay so I ordered it.
For Mechanical disc's the reviews point toward the BB7 spyre or the Klamper with the spyre reported as the best value.

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Re: Specific heat absorption capacity of disc brakes

Post by eCue » Dec 15, 2017 9:20 pm

I bought a set of Nexus brake levers for the roller brake , they have a switch for long or short pull brakes. Found out I will also need to use them in short pull mode with the Spyre caliper as its made for cyclocross bikes with short pull levers.
see article ~ http://www.cxmagazine.com/trp-new-spyre ... ual-piston

The main difference between the Spyre's and BB7's are the spyre's use dual pistons one on each side vs the bb7's single piston.

TRP offers a v-brake compatible version for long pull levers called "Spyke" for the fat and mountain bike market.

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Re: Specific heat absorption capacity of disc brakes

Post by Chalo » Dec 15, 2017 10:12 pm

My coworker who's used several kinds of mechanical discs on his polo bike says he thinks TRP (Tektro) Spyke is a little stronger than Avid BB7, but he prefers BB7 because Spyke requires much more frequent adjustment.
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Re: Specific heat absorption capacity of disc brakes

Post by liveforphysics » Dec 15, 2017 11:50 pm

You ultimately win at brakes through whatever mechanism enables the highest rates of energy transfer.

This is why racecar brake rotors float on the disc mounting hat, and just operate glowing red visibly while braking.

Brakes on F1 cars use carbon-ceramic rotor materials to glow at 1200degC to transfer heat. With all the exotic materials and tech people put into bikes, I'm amazed high-end road bikes aren't already running tiny floating carbon-ceramic rotors that weigh just a few grams and glow braking from big descents.

This page has some interesting brake design optimization photos.

https://www.formula1.com/en/championshi ... rakes.html
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Re: Specific heat absorption capacity of disc brakes

Post by eCue » Dec 16, 2017 12:09 am

The mechanics of the TRP are a superior design to the bb7's which despite their short comings have worked well for people as the online reviews denote.

If I had know of them I may well of went with the below hy / rd version that is reported to have a improved response. It weighs in heavy for those who care @ 198 gr. , without Rotor.

Image


The more I learn the more I discover I knew less then I had thought , The nexus levers turned out to have 3 brake pull settings

C setting for cantilever brakes
R setting for roller brakes
V setting for v-brakes with power modulation

BL-IM65
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180 gram
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Re: Specific heat absorption capacity of disc brakes

Post by Chalo » Dec 16, 2017 1:21 am

Oddly, when Nexus roller brake levers were made with just one pull ratio, it was the wrong one for roller brakes. They were very squishy and easy to pull all the way to the grip.

Roller brakes, like other drum brakes, are very finicky about lever travel. Avid Speed Dial are about right when they're dialed all the way to their highest mechanical advantage/shortest pull. Also, "compressionless" brake housing seems to help when using a canti type lever. I like a long blade (four finger) lever in combination with drums.
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Re: Specific heat absorption capacity of disc brakes

Post by eCue » Dec 16, 2017 3:54 am

Im thinking all brakes are extremity sensitive to their levers pull not so much RB in particular more so in the same way as other brakes and levers are effected.
When reading up on RB's I had found people were quite happy using long pull v-brake levers with RB's some defending them as superior as they would set them looser apparently for less brake drag. Others wrote it made the lever pull too firm without much leverage.
Using Canti levers with v-brakes or vice versa makes for the wrong feel in a same way as with RB's.
Shimano really does make some oddball parts .. too many of them..

A youtube brake testing video using a Flir a rim brake a disc brake and drum brake of some kind
[youtube] https://www.youtube.com/watch?v=tqMuxfHd9Vg[/youtube]
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Re: Specific heat absorption capacity of disc brakes

Post by Epyon » Dec 16, 2017 9:51 pm

Epyon wrote:
Dec 14, 2017 3:41 am
Look into TRP Spykes. Leaps and bounds above the BB7s. You can probably find them for around $50 (per caliper). Then you'll need a lever. Avid Speed Dial 7s are great. Or if you have older V-brake ratio levers on hand, you could run TRP Spyres.
I meant canti instead of v-brake there. Looks like you got it all figured out though.

Chalo wrote:
Dec 15, 2017 10:12 pm
My coworker who's used several kinds of mechanical discs on his polo bike says he thinks TRP (Tektro) Spyke is a little stronger than Avid BB7, but he prefers BB7 because Spyke requires much more frequent adjustment.
Really? I found the opposite. Since the both pads pull, you would never have to adjust the inner (stationary) pad in.
liveforphysics wrote:
Dec 15, 2017 11:50 pm
Brakes on F1 cars use carbon-ceramic rotor materials to glow at 1200degC to transfer heat. With all the exotic materials and tech people put into bikes, I'm amazed high-end road bikes aren't already running tiny floating carbon-ceramic rotors that weigh just a few grams and glow braking from big descents.
Carbon rotors are available and have been used on downhill mountain bikes. The rotors don't keep enough heat in them to be "grippy", so organic pads are used, but they wear quickly.

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Re: Specific heat absorption capacity of disc brakes

Post by Chalo » Dec 16, 2017 10:16 pm

Epyon wrote:
Dec 16, 2017 9:51 pm
Chalo wrote:
Dec 15, 2017 10:12 pm
My coworker who's used several kinds of mechanical discs on his polo bike says he thinks TRP (Tektro) Spyke is a little stronger than Avid BB7, but he prefers BB7 because Spyke requires much more frequent adjustment.
Really? I found the opposite. Since the both pads pull, you would never have to adjust the inner (stationary) pad in.
He finds that Spykes self-loosen and BB7s don't.
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Re: Specific heat absorption capacity of disc brakes

Post by DRMousseau » Dec 16, 2017 11:11 pm

I'd like to thank ya'll here,... as brakes are very important to me, as is the info gleaned in all these posts.

A bit more critical of vehicle brake fade, heat and function, than are other typical vehicle drivers, I wondered of such on bike systems. IMO, it's barely noticeable, but then I'm an old man that no longer screams downhill or at top speed anymore, and use regen A LOT. I AM surprised that I've not seen "free floating" calipers, neither single nor dual, around the rather delicate disks of bicycles. But they seem forgiving enough to generally be unnecessary outside of specialized needs. Adjustments of recent designs seems simple and minimal, and I DO like the positive solidness of the BB-7. Still considering others perhaps, for my current "overly heavy" project,... as brakes are DAMN important to me. And good smooth solid levers are too,... I really hate the feel of most under my fingers, but exploring better options thanks to ya'll.

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Re: Specific heat absorption capacity of disc brakes

Post by eCue » Dec 17, 2017 12:11 am

Epyon wrote:
Dec 16, 2017 9:51 pm
Epyon wrote:
Dec 14, 2017 3:41 am
Look into TRP Spykes. Leaps and bounds above the BB7s. You can probably find them for around $50 (per caliper). Then you'll need a lever. Avid Speed Dial 7s are great. Or if you have older V-brake ratio levers on hand, you could run TRP Spyres.
I meant canti instead of v-brake there. Looks like you got it all figured out though.
After I figured it out thought you may of meant the first series as they were canti's

I have a set of Shimano's 1st v-brake the m600 I believe it is from '95
If you go back to the early 90's the first Xt brakes were cantilevers , same as with XTR brakes strange as it sounds.

First generation XT brake levers BL-m700
Image

Circa 1992

First generation XTR canti brakes M900
Image
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Re: Specific heat absorption capacity of disc brakes

Post by Chalo » Dec 17, 2017 12:47 am

1st gen XTR, last gen cantilevers. I wasn't sorry to see cantilevers go away, but I was sorry to see them return with the cyclocross bike marketing phenomenon.

The only things I can say in favor of cantilever brakes are that you can tune them to match specific levers, and they can be set up to clear big fat tires. Everything else about them is a minus.
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Re: Specific heat absorption capacity of disc brakes

Post by liveforphysics » Dec 17, 2017 3:46 am

Road bike brakes don't clear the mud off the tires to keep pedaling in my cyclocross raceing. Disc's give a consistent function and feel no matter how muddy the rims and tires are by the end of the race.

I also tend to get a good deal of wheel deformation run out by the end of a hard ride or race that requires disconnecting that brake to not eat try speed penalty of the rim to pad bumping friction.

Just like any brakes, disc can be done badly, or set up to feel and function amazing.
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disc brake pads

Post by eCue » Dec 17, 2017 11:12 am

Question for liveforphysics and other members , what brake pads do you prefer on the cyclo bike and why ?

It would good to have other members dics pad preferences and reasons for them so we can learn more of each pad.
Although it may be anecdotal people preferences could be for the same set of pads or same few sets of pads.
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Re: Specific heat absorption capacity of disc brakes

Post by E-geezer » Dec 17, 2017 7:15 pm

Solid rotors for mud unless you like buying disc pads....... 8)
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Re: Specific heat absorption capacity of disc brakes

Post by eCue » Dec 18, 2017 1:17 am

I read organic pads are best upfront where power and feel are needed and metallic pads in the rear as less force is required and they provide longer life.
Problem with organic pads is short life , some people will use a semi metallic pad up front to counter this.
To avoid changing pads every 3 or 4 months thinking of using a semi metallic pad upfront of some description.

This is with generally dry road condition with rain showers thrown in at Mother Nature discretion

Shimano pads fit TRP calipers
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