The physics of disc brakes

Discuss light weight issues concerning road bikes & parts.

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sanbaronto
Posts: 30
Joined: Sun May 12, 2019 1:06 pm

by sanbaronto

As you probably know, Froome spoke his opinion on disc brakes. And he did not like them.
https://youtu.be/vRoXYeNueTk

Here is a very good explanation of the challenges of making road disc brakes: https://youtu.be/aJK_d6onNjo

- Much heat due to braking from high speeds
- Increasing pad to rotor clearance will cause either reduced brake power, or increased brake lever travel
- Road disc brakes are made to be lighter (and smaller, more aero) than mtb disc brakes, but the demands on the road suggests otherwise.

So is it impossible to make a disc brake good enough? Would you accept more weight and worse aerodynamics to reduce some of the problems we see today?

MaxPower
Posts: 283
Joined: Fri Sep 20, 2019 9:30 pm

by MaxPower

sanbaronto wrote:
Mon Feb 08, 2021 5:51 pm
As you probably know, Froome spoke his opinion on disc brakes. And he did not like them.
https://youtu.be/vRoXYeNueTk

Here is a very good explanation of the challenges of making road disc brakes: https://youtu.be/aJK_d6onNjo

- Much heat due to braking from high speeds
- Increasing pad to rotor clearance will cause either reduced brake power, or increased brake lever travel
- Road disc brakes are made to be lighter (and smaller, more aero) than mtb disc brakes, but the demands on the road suggests otherwise.

So is it impossible to make a disc brake good enough? Would you accept more weight and worse aerodynamics to reduce some of the problems we see today?
Give it some generations. It will come and be doable for road. It just takes time and some development cycles to get it where it needs to be.

Just stop believing in marketing (and that's for everything, not just cycling. Marketing-talk is poison and a area so gray i would call it a lie in many instances).

Disc's are not the mechanical wonder that ends all development in the cycling industry. Development cycles are for one thing, and one of thing only - making yesteryears technology obsolete so you will buy more stuff.

by Weenie


cloud9blue
Posts: 69
Joined: Wed Sep 09, 2020 3:49 pm

by cloud9blue

It is beating a horse to death at this point, each has its pro and con.

I got both rim and hydrualic Red etap setup. Rim brake is definitely better ergonomically if you prefer minimal lever travel and modern carbon rims and it works just as well as the hydrualic disk in dry weather. Whereas disc will work no matter what you throw at it, assuming you dont mind a bit of rub or noise if you got too much dirt or mud stuck on it. However, the long dead travel is rather annoying to me (even when properly adjusted).

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LeDuke
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Location: Front Range, CO

by LeDuke

One of the problems is that he’s on a trash set up.


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Mr.Gib
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Location: eh?

by Mr.Gib

It's discouraging. Love my discs and how the leave the rim alone, but the physics are limiting in a road application. I have always hoped that it was just a matter of time until technology would give us something closer to perfection, but I am starting to think that unless we are prepared for bigger and heavier everything, disc braking on road bikes will always be less than it could be.
wheelsONfire wrote: When we ride disc brakes the whole deal of braking is just like a leaving a fart. It happens and then it's over. Nothing planned and nothing to get nervous for.

TheRich
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Joined: Tue Jan 01, 2019 1:36 am

by TheRich

LeDuke wrote:
Mon Feb 08, 2021 6:08 pm
One of the problems is that he’s on a trash set up.


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and a crap brand ambassador

spartacus
Posts: 345
Joined: Mon Apr 04, 2011 6:53 pm

by spartacus

What are you guys smoking? The "physics are limiting"? Wut? The disc brakes are far more powerful than rim brakes. If you are overheating them then you would have probably done something bad to a carbon rim with rim brakes too. Aluminum rims brake good but still have less power than discs.

pmprego
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Joined: Mon Jan 21, 2019 3:16 pm

by pmprego

spartacus wrote:
Mon Feb 08, 2021 6:55 pm
What are you guys smoking? The "physics are limiting"? Wut? The disc brakes are far more powerful than rim brakes. If you are overheating them then you would have probably done something bad to a carbon rim with rim brakes too. Aluminum rims brake good but still have less power than discs.
The circunference of a rim has nothing to do with the one from a disc. That's the thing about heating up.

JMeinholdt
Posts: 523
Joined: Wed Feb 26, 2020 10:31 pm
Location: Topeka, KS

by JMeinholdt

spartacus wrote:
Mon Feb 08, 2021 6:55 pm
What are you guys smoking? The "physics are limiting"? Wut? The disc brakes are far more powerful than rim brakes. If you are overheating them then you would have probably done something bad to a carbon rim with rim brakes too. Aluminum rims brake good but still have less power than discs.
I disagree. Yes they're more powerful, and no the physics aren't limiting. The problem isn't that they overheat to failure, it's that it doesn't take much heat at all to cause rubbing. I don't have much in the way of descents where I'm from, but it only takes about 10 seconds of relatively hard braking to get the front disc on my 3T to rub for about 30-60 seconds until it cools down.

Obviously, this isn't in any way detrimental to braking performance, but it is an annoyance.
Wilier Cento10AIR Rim Brake - SRAM Force AXS
3T Exploro 105 - Gravel/Commuter/Trainer

Strava link: https://www.strava.com/athletes/jmeinholdt
YouTube link: https://www.youtube.com/channel/UCTGn14 ... N_N-wHlViQ

TheBeautifulOne
Posts: 21
Joined: Tue Nov 24, 2020 7:53 pm

by TheBeautifulOne

Don't know about you guys but last time i checked Froome wasn't listed as an engineer.

Seriously though, disc brakes have been proven over and over across many industries, there are no theoretical nor practical reasons why should they work on road bicycles. As for the overheating, this is total BS. Unless you brake really heavily over 10km descent and then suddenly stop and let brakes dissipate heat freely, this is not an issue.

spartacus
Posts: 345
Joined: Mon Apr 04, 2011 6:53 pm

by spartacus

JMeinholdt wrote:
Mon Feb 08, 2021 7:30 pm
spartacus wrote:
Mon Feb 08, 2021 6:55 pm
What are you guys smoking? The "physics are limiting"? Wut? The disc brakes are far more powerful than rim brakes. If you are overheating them then you would have probably done something bad to a carbon rim with rim brakes too. Aluminum rims brake good but still have less power than discs.
I disagree. Yes they're more powerful, and no the physics aren't limiting. The problem isn't that they overheat to failure, it's that it doesn't take much heat at all to cause rubbing. I don't have much in the way of descents where I'm from, but it only takes about 10 seconds of relatively hard braking to get the front disc on my 3T to rub for about 30-60 seconds until it cools down.

Obviously, this isn't in any way detrimental to braking performance, but it is an annoyance.
I've experienced this a little bit too and just ignore it :oops: On my MTB I'm too busy trying not to die to notice but on the road bike it's easier to tell.

spdntrxi
Posts: 4189
Joined: Sat Jul 20, 2013 6:11 pm

by spdntrxi

I get a little ting here and there sprinting.. usually on hard descents, I'll get some honking for 5-10s max. which feels like forever.
2019 BMC TM01 Road UCI config 7.36kg

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wheelsONfire
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Location: NorthEU

by wheelsONfire

If you are honest and say that disc brakes do rub, sooner or later, someone take a verbal piss on you. They do rub that's nothing new.
Disc brakes do however have better modulation and stopping power to. So you can't get it all.
Can't understand why this debate never ends!
Fact is rim brakes will go away either anyone here likes it or not.
Last edited by wheelsONfire on Mon Feb 08, 2021 9:01 pm, edited 1 time in total.
Bikes:

Ax Lightness Vial EVO Race (2018.12.21)
viewtopic.php?f=10&t=156137
Paduano Racing Fidia (kind of shelved)
Open *UP* (2016.04.14)


Ex bike; Vial EVO D

Hexsense
Posts: 1818
Joined: Wed Dec 30, 2015 12:41 am

by Hexsense

Normally it's Shimano ice-tech freeza road rotors that warp easily at low heat (however, it also cool down fast thanks to the fins).

But Israel Startup Nation use Swissstop disc rotors and pads. Swissstop disc rotors are relatively heavy. That should have better thermal capacity than many other light weight rotors.
On the pad side, Swissstop Disc RS pads aren't powerful, yes. But it's quieter than most other pads.
Eitherway, his not so impressed opinion is also not good for Swissstop.

EDIT: I just saw that Swissstop released a new race version of their rotor that shave some grams from their standard version. Since the normal version already have problem with heat, race version could only be worse, right?
https://www.instagram.com/p/CK4NA_ylDFj/

by Weenie


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Alexbn921
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by Alexbn921

If you disks rub then something is wrong, Period! Disks have significantly higher thermal capacity and friction levels. This is not debatable. Hydraulic systems have almost zero friction with better feel.

You need to true disks just like wheels. Mine are true to +-.001inch, just like my wheels.

Frame mounting surfaces need to be flat and perpendicular to the wheels. Just like BB’s, manufactures screw this up.

Frames need to be reinforced to handle the different loads and this adds weight. It can also compromise ride feel if done poorly.

Other than weight MY disks perform better in every measurable way and I will never ever give them up. In fact, they have saved my life. Take care of your bike and it will take care of you.

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