The Great Braking Debate Thread (Disc/Rim/Cantilever/Fixie/InsertNewTechHere)

Discuss light weight issues concerning road bikes & parts.

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TobinHatesYou
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by TobinHatesYou

Lina wrote:
Thu Oct 28, 2021 8:06 am

Surely not having to have a braking surface on the rim allows for better aerodynamics where the tire meets the rim. Not sure if that's enough to counteract the additional spokes though. Also we do have plenty of examples from early carbon frames why bonding aluminium and carbon isn't probably the best idea.

Plus with full carbon construction, we aren't really limited by spoke count. We can make very strong solid bladed carbon spokes or big hollow sections like BikeAhead and Black Inc have done.

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tjvirden
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by tjvirden

I think the last few pages show just why it's such a difficult subject to discuss - the complexity of balancing so many factors.

Another one that hasn't been brought up much is brake choice in relation to tubes/tubeless+sealant - I've never tried rim brakes and tubeless+sealant; one reason being that I'm suspicious of the function under sustained, hard braking.

Braking induced heat is still a real difficulty with rim brakes and, as has been hinted at, it's not so much about pressure change (that has been measured to be small - about 5 to max 10% on aluminum clincher rims with "road" pressures and tire size), but high rim temperature resulting in poor tire retention. Tubeless tires should help with that, but I'm not at all sure that sealant at high temperature [at least 100 C] is so practical.

jasjas
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by jasjas

bikeboy1tr wrote:
Thu Oct 28, 2021 2:22 am
Remember the days when the Pros would descend a long pass that required extended brake time which would create enough heat to soften or melt the glue on their tubulars resulting in crashes in the corners due to rolled tires. Its not something we see any longer and I would think carbon rims dissipate heat better than alum. That alone proves that enough heat is created when braking for extended periods of time.
No i don't remember because it rarely happened and only then when road surface/air temps were extremely high, using 23mm tubs and hi pressures.

If an alloy rim gets so hot, as to melt tub glue it will also destroy a tube as well.

Carbon is a poor dissipator of heat.

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tanhalt wrote:
Wed Oct 27, 2021 7:10 pm
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openwheelracing
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by openwheelracing

I don't remember rim brake issue last couple years in pro peloton. I remember rim brake dominating the sport though. I do remember several disc brake issues. However, that's likely due to majority riders only sponsored by disc brakes now. Only UAE and Ineos have a choice to switch to rim. Hopefully ISN follows.

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wheelsONfire
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by wheelsONfire

RyanH wrote:
Wed Oct 27, 2021 5:28 pm
We should also remember that topography and climate vary significantly around the world. Norcal is often wet and has steep terrain, so consistent braking power would be welcomed there. Socal has steep terrain but rains like 5x a year and last time it rained on our Saturday group ride that goes up PCH, our typical group of 50-100 people became 5 of us, all on rim brakes except 1. Point being is that in Socal, we don't need to ride in the rain since it so seldomly rains. Other areas rain frequently but they're flatter which is where you get situations like those in the UK that find the constant noise tiring and end up switching back to alloy wheels for commuting because alloy is good enough for that terrain.

When you remove wet weather performance, benefits of disc are primarily: braking performance is decoupled from the rim so braking performance is consistent regardless of wheel choice, wider tire clearance, you can safely use carbon clinchers and cheaper consummables. I think a lot of folks on rim brake setups haven't experienced a good rim brake setup, because if you have, the feel is roughly the same, I'm pretty sure road disc designers did that on purpose. I've been doing a lot of A to B comparison the past two weeks and my street is over 10% grade so right out the door, I have to grab a handful of brake at the bottom of my street. Every time I got onto my Litespeed with Bontrager XXX and ee brakes, I was surprised that the brake feel was very very similar to the Campy Ekar setup. The campy setup is a lot firmer lever throw and less travel, so I have to adjust my modulation effort but in trying to control my speed on a >10% grade, they feel the same. But, and this is a big but, of the two dozen or so carbon wheelsets I've had, the Bontrager XXX have the best feel and a minority have what I'd consider good brake surfaces. So, the value in decoupling brake performance from the rim is huge, particularly when it comes to carbon rims. With that being said, a set of HED Belgiums and swisstop pads are going to feel just as good as disc and probably be a lighter setup.
Do you consider SwissStop as the best brake pads?
I have tried a few and i don't. Just curious how you and others feel.
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by Mr.Gib

tanhalt wrote:
Thu Oct 28, 2021 1:34 am
But, instead of re-evaluating the design decision of making rims completely out of carbon, the decision was made to add a completely separate braking surface at the hub, the result being a larger weight gain than if they'd just used an aluminum brake track on the rims...and in the process made the wheels overall heavier and less aerodynamic (need more spokes and material to account for torque transfer from hub to the rim).
This is a very clever analysis of the evolution of the braking transformation in road cycling. Can't blame the industry though, this one is on the consumer. And I don't blame the consumer either - that silver ring just doesn't look as good as an all black wheel so we won't buy a carbon wheel with an alloy brake track. We are a shallow group.

Been following the rim/disk debate and never felt strongly in favour of one or the other no matter what arguments were made. In fact, absent the impact on future availability, I could not pick one over the other even if I was forced to make a choice. Perhaps I prefer riding my rim bike, but prefer stopping on my disc bike. Net is a wash. Glad I have both.
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.

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by Mr.Gib

Lina wrote:
Wed Oct 27, 2021 11:59 pm
...When the recipe to stop disc brakes from being noisy and howling is exactly the same. And even the instructions on how to make it happen have been already shared in this thread, like every disc brake thread for the last couple of years.
OK, I'm pulling off the gloves now, might even get banned. My disc brakes are perfectly silent. In fact all of my riding buddies disc brakes are perfectly silent. Even strangers disc brakes are silent, when I watch pro racing, road and cyclocross - their brakes are silent also...accept when they are cold and wet. And then they all make noise. Sometimes a lot of noise. But heat them up and dry them off with a good hard braking effort, and presto, silent again. You gonna tell me that all these brakes are set up improperly? Please tell me what I am supposed to change with my perfectly set up disc brakes that are silent 95 percent of the time?

Lina wrote:
Wed Oct 27, 2021 11:59 pm
My disc brakes are quiet outside of some niche situations.
hmm, wonder what those niche situation are. :roll:
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.

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by tanhalt

Mr.Gib wrote:
Thu Oct 28, 2021 5:01 pm
tanhalt wrote:
Thu Oct 28, 2021 1:34 am
But, instead of re-evaluating the design decision of making rims completely out of carbon, the decision was made to add a completely separate braking surface at the hub, the result being a larger weight gain than if they'd just used an aluminum brake track on the rims...and in the process made the wheels overall heavier and less aerodynamic (need more spokes and material to account for torque transfer from hub to the rim).
This is a very clever analysis of the evolution of the braking transformation in road cycling. Can't blame the industry though, this one is on the consumer. And I don't blame the consumer either - that silver ring just doesn't look as good as an all black wheel so we won't buy a carbon wheel with an alloy brake track. We are a shallow group.
Thanks. I just "calls them as I sees them" :)

There are solutions to that "silver ring" aesthetic issue. Look at the wheels on that Cannondale I posted above. I can't count how many times people have told me they thought the rims were all carbon...and, like I said earlier, despite the black coloring being just an anodized coating, the engraved radial groove texturing seems to "protect" the coating from being worn away by embedded grit in the pads (my suspicion is "pad cleaning" on initial pad application).

Here's a close-up after >5k miles of pavement riding (including many large climbs and descents) and ~2300 miles of mixed pavement/dirt use (heavy on the dirt).
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by RyanH


wheelsONfire wrote:
Do you consider SwissStop as the best brake pads?
I have tried a few and i don't. Just curious how you and others feel.
My 3 go to pads are SS Black Prince, Campy Red and Reynolds Power Pro. It depends on the texture of the rim. I find swissstop best on textured rims. Campy seems to be good on most others (including lasered rims) and Reynolds are my go to back when I had old school smooth rims.
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by maxim809

tanhalt wrote:
Thu Oct 28, 2021 1:34 am
<Snip>
It seems to me there's quite a bit of system "mis-optimization" (i.e. optimizing performance properties that aren't necessarily the main performance drivers, at the expense of those that are) in bike designs.
Great post.

To expand your last bit... how one optimizes is the crux of all complex debates, isn't it?

Aesthetics plays a part of the final optimization, especially in this sport. Often times, the optimal engineering solution needs to be compromised so that the wheels don't look janky as modern, conventional fashion wisdom dictates.

Taking a step back... every design has Quantitative and Qualitative factors to it. That which can be measured, versus that which can only be observed and is hard to measure (if not impossible). There are the engineering optimizations in the former, and then "damn dude, I'll ask you wut, should we just black out these rims using carbon, or black anodize these brake tracks so they look cool?" in the latter.

Each designer will have different opinions on how to balance the factors that feed into these 2 categories, so "one man's optimization is another man's mis-optimization".

Which is a very roundabout way of saying... people value different things. Mind blowing, I know. Hehe.

This will continue to be the theme until the universe disappears.

tanhalt
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by tanhalt

Lina wrote:
Thu Oct 28, 2021 8:06 am
Going from 20 C to 80 C gives ~1 bar pressure swing at road temperatures which does have an impact on riding quality. And you run into heat problems with inner tubes.
I think you'd be hard-pressed to verify that the average air temp inside a bicycle tire varies by that much, even after intense braking. As was mentioned in another post above, actual pressure measurements show variations quite a bit smaller than that. If that that temp data exists, I'd love to see it.
Lina wrote:
Wed Oct 27, 2021 11:59 pm
Surely not having to have a braking surface on the rim allows for better aerodynamics where the tire meets the rim. Not sure if that's enough to counteract the additional spokes though. Also we do have plenty of examples from early carbon frames why bonding aluminium and carbon isn't probably the best idea.
That's been often asserted/speculated...and yet, I haven't seen any examples of this, or actual data, and wheel rim manufacturers have had plenty of time to make those changes. Then again, if one realizes that prior to the common use of disc brakes on road bikes, aero rim designers basically "ignored" the fact that braking was taking place on the brake track area in regards to shape, then it makes sense why that hasn't come to fruition. I can point to plenty of examples of aero wheels that had aero shaped brake tracks, and not the assumed "parallel" configuration. This was even done on some lower profile aluminum rims, such as the old Zipp 101s.

Also, an aluminum insert, such as a threaded BB shell in a carbon frame, is quite a different use case than a (mostly) non-structural carbon "cap" bonded to an aluminum rim...and I don't recall any large issues with the Hed Jet wheels in that regard, which have been in production/use for quite a LONG time.

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by Maddie

What's the lightest carbon wheel with alloy brake track available? I remember reading nearly as light or a few 10s of grams heavier than disc wheelset. Should be tubeless, preferably with hooks.

tomato
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by tomato

Maddie wrote:
Thu Oct 28, 2021 8:07 pm
What's the lightest carbon wheel with alloy brake track available?
HED Jets ?

daninplymouth
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by daninplymouth

After using both its disc's for me. Although rim brakes are fine in 90% of situations if you get caught in bad rain mine were next to useless. So much so if I had to perform any kind of emergency stop I would've been off

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