Road Discs

On 27/09/17 04:09, Frank Krygowski wrote:
On 9/26/2017 4:38 AM, James wrote:
On 26/09/17 13:06, Frank Krygowski wrote:
On 9/25/2017 6:00 PM, jbeattie wrote:
People are willing to accept the weight and aerodynamic penalty with
discs, apparently on the belief that ordinary rim brakes are
inadequate or because they want to use CF wheels. Who knows.

Many people are willing to accept anything that's in fashion in their
own little world. Fashion is amazingly powerful, and doesn't need to
make any particular sense.

At least we can claim that disc brakes are marginally more useful than
tattoos.


If a person wants to use wheels with CFRP rims, a bike with disc
brakes makes sense.

CFRP rims with rim brakes usually work ok in dry conditions provided
the correct brake blocks are used. Some CFRP rims can be damaged if
the wrong pads are used, and some have been damaged even with the
"correct" pads.

But in wet conditions, the braking performance is generally very much
worse.

Disc brakes solve those problems, and allow rim manufacturers to save
more grams because there's no need for a braking surface.

I'm not saying there are never benefits to disc brakes, and I don't
think anyone else is saying that.

I would never tell Jay he shouldn't use discs; his commuting regimen in
hilly, rainy Portland is perfect for them.

So yes, discs have some advantages. They also have some disadvantages,
and those disadvantages become known only through discussions something
like this one. Advertisers are certainly not going to spend much time
listing the disadvantages.

And the typical consumer isn't going to think about these things at all,
beyond "Oooh, disc brakes. They use them on motorcycles, so that's what
I need! I'll never buy a bike without them things!"

We're supposed to be better than that. We should consider both
advantages and disadvantages. It happens to be my judgment that for
almost all road cyclists, the disadvantages outweigh the advantages.
Almost everyone would be better off with more normal brakes.

What is "almost everyone" if it is not the set of people minus a small
subset? Did I not identify a subset as "a person [who] wants to use
wheels with CFRP rims"?

Surely everyone minus a small subset equals almost everyone?

If it was because I elaborated on Jay's comment that made you think
something else, you're reading too much between the lines.

--
JS

On 9/27/2017 8:25 PM, James wrote:
On 27/09/17 04:09, Frank Krygowski wrote:
On 9/26/2017 4:38 AM, James wrote:
On 26/09/17 13:06, Frank Krygowski wrote:
On 9/25/2017 6:00 PM, jbeattie wrote:
Â*People are willing to accept the weight and aerodynamic penalty with
discs, apparently on the belief that ordinary rim brakes are
inadequate or because they want to use CF wheels. Who knows.

Many people are willing to accept anything that's in fashion in their
own little world. Fashion is amazingly powerful, and doesn't need to
make any particular sense.

At least we can claim that disc brakes are marginally more useful than
tattoos.


If a person wants to use wheels with CFRP rims, a bike with disc
brakes makes sense.

CFRP rims with rim brakes usually work ok in dry conditions provided
the correct brake blocks are used.Â* Some CFRP rims can be damaged if
the wrong pads are used, and some have been damaged even with the
"correct" pads.

But in wet conditions, the braking performance is generally very much
worse.

Disc brakes solve those problems, and allow rim manufacturers to save
more grams because there's no need for a braking surface.

I'm not saying there are never benefits to disc brakes, and I don't
think anyone else is saying that.

I would never tell Jay he shouldn't use discs; his commuting regimen in
hilly, rainy Portland is perfect for them.

So yes, discs have some advantages. They also have some disadvantages,
and those disadvantages become known only through discussions something
like this one. Advertisers are certainly not going to spend much time
listing the disadvantages.

And the typical consumer isn't going to think about these things at all,
beyond "Oooh, disc brakes. They use them on motorcycles, so that's what
I need! I'll never buy a bike without them things!"

We're supposed to be better than that. We should consider both
advantages and disadvantages. It happens to be my judgment that for
almost all road cyclists, the disadvantages outweigh the advantages.
Almost everyone would be better off with more normal brakes.

What is "almost everyone" if it is not the set of people minus a small
subset?Â* Did I not identify a subset as "a person [who] wants to use
wheels with CFRP rims"?

Surely everyone minus a small subset equals almost everyone?

If it was because I elaborated on Jay's comment that made you think
something else, you're reading too much between the lines.

I was not trying to disagree with you, James. I don't see anything that
I wrote above that should be interpreted as disagreement with you.

I'm saying that yes, discs have certain advantages. You described one.
I'm saying that we should also discuss disadvantages. I hope that's clear.

--
- Frank Krygowski

On Wednesday, September 27, 2017 at 3:18:31 PM UTC-7, Doug Landau wrote:
On Tuesday, September 26, 2017 at 7:57:06 PM UTC-7, Frank Krygowski wrote:
On 9/26/2017 8:34 PM, John B. wrote:
On Tue, 26 Sep 2017 07:18:28 -0700 (PDT), jbeattie wrote:

"Braking is also more rapid and positive with a well adjusted disc."

I would really like to see the dynamics of that statement explained as
during the 20 years or so that I worked on aircraft it was always
explained to us that maximum braking force is generated just before
the tire starts to skid which I have always assumed applied to any
rubber tired wheel and thus any brake that could actual stop the wheel
from turning must be capable of generating maximum braking force.

I've thought a bit about the descriptions of brake behavior. What you
say about maximum deceleration occurring very near skidding is certainly
correct. But what about statements like Jay's "rapid and positive," or
others' descriptions of "progressive" or "controllable" and the like?

In a straight line. He is still only considering the situation of moving in a straight line. While turning, maximum braking will occur at a lower point than the coefficient of friction of the tires, and the result of exceeding the available traction will be a spin and fall, rather than a skid.

I was thinking about wet braking. Discs engage faster and with more braking force than rim brakes because you're not drying the rims, and the pad force is higher in discs. In dry weather, I'd only bother with a disc if I had CF rims or was mountain biking or doing exceedingly steep descents on a gravel bike. My hands did get tired with rim brakes on a recent gravel descent.

-- Jay Beattie.

On Monday, September 11, 2017 at 8:52:16 AM UTC-7, jbeattie wrote:
On Sunday, September 10, 2017 at 9:11:16 AM UTC-7, AMuzi wrote:
On 9/9/2017 5:28 PM, jbeattie wrote:
So, my SuperSix was crushed in a roof-rack accident and last weak my Roubaix was stolen out of the garage that I left open all night. I've done that many times -- apparently one too many. I'm down to a gravel bike and my commuter -- the reborn warranty CAADX (which is a great bike).

The gravel bike is a pig, but I'll use that for fall/winter/spring sport riding. I want a fast bike, though -- and I've got a line on a nice bike that I can get with rim brakes or discs, but the disc model will not be available until December -- which really means that I get to ride it in dry weather some time around May. I can get a rim brake model by the end of the month.

All the shops are pushing discs, and I did like the discs on the Roubaix and on my gravel bike. I know this is absolutely the wrong group to ask because it's wall-to-wall curmudgeons, but if you were buying your last nice road bike, would you go rim brakes or discs? It will be a dry weather bike or ridden in the rain only because of bad luck. There would be no real weight penalty because the bike is so light to start with. I'm not aero, so I don't care about the aero penalty with discs.

My concern with getting rim brakes is not really even a performance issue because in dry weather, I've never had a problem with rim brakes -- but to listen to the guys at the local shop, rim brakes are going the way of the dodo. I'm worried about buying an antique!

No suggestion on your specific question but speaking as an
Industry Professional, I think my record for selling one
customer his "final perfect bike to last the rest of my
life" is six bicycles, 3 or 4 is amazingly common. Many of
those guys will be back again too.

So much of this is just market-driven angst. Discs have a nice feel and are powerful and do work better in the rain, but that is different from rim brakes being inadequate or dangerous.

People develop a preference and then the last-thing becomes unworkable or dangerous. "I used to ride 23mm tires, but 25s are so much more positive. You'll die riding 23mm tires!" Then I think, "didn't I race on 19mm and 21mm?"

I was talking to my son yesterday, and he rides an Emonda with rim brakes and CF wheels. So, I asked him "where did you ride today," and he says Big Cottonwood with some side routes and a climb on the way home -- maybe 6,000 -7,000 feet of climbing and some seriously steep descending on the side routes. Any problems? No. His friends use rim brakes, and they do ridiculous amounts of climbing -- one just did 31,000 feet in a day (the whole Everest thing). And then I think back on my decades of rim brake experience and wonder why I'm even worried -- except for the anxiety caused by choices. Not that discs would be super-sweet and maybe even reduce some hand fatigue, but the idea that they are necessary or that rim brakes are dangerous is kind of out there.


-- Jay Beattie.

I am surprised that you, of all people, are asking us. :-)

I like rim brakes because we all know so well how to set them up, and their failure modes come up predictably (worn pads, etc.).

My local climb is close to 15% with lots of places you don't want to fall off. Plus the road is narrow and has occasional idiots. I would slightly prefer to have good disks here, I think, but it's not worth making the change. If the descent were any easier, I wouldn't even consider disks.

My suspicions about disks are simply that there's more to go wrong, and those failures are more likely to be total or near-total loss of braking. It's easier to spring a leak than to suddenly snap a cable.

Peter

On 9/28/2017 7:51 AM, Peter Smith wrote:
On Monday, September 11, 2017 at 8:52:16 AM UTC-7, jbeattie wrote:
On Sunday, September 10, 2017 at 9:11:16 AM UTC-7, AMuzi wrote:
On 9/9/2017 5:28 PM, jbeattie wrote:
So, my SuperSix was crushed in a roof-rack accident and last weak my Roubaix was stolen out of the garage that I left open all night. I've done that many times -- apparently one too many. I'm down to a gravel bike and my commuter -- the reborn warranty CAADX (which is a great bike).

The gravel bike is a pig, but I'll use that for fall/winter/spring sport riding. I want a fast bike, though -- and I've got a line on a nice bike that I can get with rim brakes or discs, but the disc model will not be available until December -- which really means that I get to ride it in dry weather some time around May. I can get a rim brake model by the end of the month.

All the shops are pushing discs, and I did like the discs on the Roubaix and on my gravel bike. I know this is absolutely the wrong group to ask because it's wall-to-wall curmudgeons, but if you were buying your last nice road bike, would you go rim brakes or discs? It will be a dry weather bike or ridden in the rain only because of bad luck. There would be no real weight penalty because the bike is so light to start with. I'm not aero, so I don't care about the aero penalty with discs.

My concern with getting rim brakes is not really even a performance issue because in dry weather, I've never had a problem with rim brakes -- but to listen to the guys at the local shop, rim brakes are going the way of the dodo. I'm worried about buying an antique!

No suggestion on your specific question but speaking as an
Industry Professional, I think my record for selling one
customer his "final perfect bike to last the rest of my
life" is six bicycles, 3 or 4 is amazingly common. Many of
those guys will be back again too.

So much of this is just market-driven angst. Discs have a nice feel and are powerful and do work better in the rain, but that is different from rim brakes being inadequate or dangerous.

People develop a preference and then the last-thing becomes unworkable or dangerous. "I used to ride 23mm tires, but 25s are so much more positive. You'll die riding 23mm tires!" Then I think, "didn't I race on 19mm and 21mm?"

I was talking to my son yesterday, and he rides an Emonda with rim brakes and CF wheels. So, I asked him "where did you ride today," and he says Big Cottonwood with some side routes and a climb on the way home -- maybe 6,000 -7,000 feet of climbing and some seriously steep descending on the side routes. Any problems? No. His friends use rim brakes, and they do ridiculous amounts of climbing -- one just did 31,000 feet in a day (the whole Everest thing). And then I think back on my decades of rim brake experience and wonder why I'm even worried -- except for the anxiety caused by choices. Not that discs would be super-sweet and maybe even reduce some hand fatigue, but the idea that they are necessary or that rim brakes are dangerous is kind of out there.


-- Jay Beattie.

I am surprised that you, of all people, are asking us. :-)

I like rim brakes because we all know so well how to set them up, and their failure modes come up predictably (worn pads, etc.).

My local climb is close to 15% with lots of places you don't want to fall off. Plus the road is narrow and has occasional idiots. I would slightly prefer to have good disks here, I think, but it's not worth making the change. If the descent were any easier, I wouldn't even consider disks.

My suspicions about disks are simply that there's more to go wrong, and those failures are more likely to be total or near-total loss of braking. It's easier to spring a leak than to suddenly snap a cable.

True, but mechanical disc brakes work just fine. No need to go the
hydraulic route.

On Thursday, September 28, 2017 at 7:15:06 AM UTC-7, jbeattie wrote:
On Wednesday, September 27, 2017 at 3:18:31 PM UTC-7, Doug Landau wrote:
On Tuesday, September 26, 2017 at 7:57:06 PM UTC-7, Frank Krygowski wrote:
On 9/26/2017 8:34 PM, John B. wrote:
On Tue, 26 Sep 2017 07:18:28 -0700 (PDT), jbeattie wrote:

"Braking is also more rapid and positive with a well adjusted disc.."

I would really like to see the dynamics of that statement explained as
during the 20 years or so that I worked on aircraft it was always
explained to us that maximum braking force is generated just before
the tire starts to skid which I have always assumed applied to any
rubber tired wheel and thus any brake that could actual stop the wheel
from turning must be capable of generating maximum braking force.

I've thought a bit about the descriptions of brake behavior. What you
say about maximum deceleration occurring very near skidding is certainly
correct. But what about statements like Jay's "rapid and positive," or
others' descriptions of "progressive" or "controllable" and the like?

In a straight line. He is still only considering the situation of moving in a straight line. While turning, maximum braking will occur at a lower point than the coefficient of friction of the tires, and the result of exceeding the available traction will be a spin and fall, rather than a skid.

I was thinking about wet braking. Discs engage faster and with more braking force than rim brakes because you're not drying the rims, and the pad force is higher in discs. In dry weather, I'd only bother with a disc if I had CF rims or was mountain biking or doing exceedingly steep descents on a gravel bike. My hands did get tired with rim brakes on a recent gravel descent.

-- Jay Beattie.

Jay, I haven't actually had that problem when fording creeks. So I find it hard to believe that people actually have a problem with it. You don't have to "dry" the rim. You only have to cut through the surface layer on a very small section. Once you're through the layer the shoes push the water out of the way.

On 28/09/17 13:54, Frank Krygowski wrote:
On 9/27/2017 8:25 PM, James wrote:
On 27/09/17 04:09, Frank Krygowski wrote:
On 9/26/2017 4:38 AM, James wrote:
On 26/09/17 13:06, Frank Krygowski wrote:
On 9/25/2017 6:00 PM, jbeattie wrote:
People are willing to accept the weight and aerodynamic penalty with
discs, apparently on the belief that ordinary rim brakes are
inadequate or because they want to use CF wheels. Who knows.

Many people are willing to accept anything that's in fashion in their
own little world. Fashion is amazingly powerful, and doesn't need to
make any particular sense.

At least we can claim that disc brakes are marginally more useful than
tattoos.


If a person wants to use wheels with CFRP rims, a bike with disc
brakes makes sense.

CFRP rims with rim brakes usually work ok in dry conditions provided
the correct brake blocks are used. Some CFRP rims can be damaged if
the wrong pads are used, and some have been damaged even with the
"correct" pads.

But in wet conditions, the braking performance is generally very much
worse.

Disc brakes solve those problems, and allow rim manufacturers to save
more grams because there's no need for a braking surface.

I'm not saying there are never benefits to disc brakes, and I don't
think anyone else is saying that.

I would never tell Jay he shouldn't use discs; his commuting regimen in
hilly, rainy Portland is perfect for them.

So yes, discs have some advantages. They also have some disadvantages,
and those disadvantages become known only through discussions something
like this one. Advertisers are certainly not going to spend much time
listing the disadvantages.

And the typical consumer isn't going to think about these things at all,
beyond "Oooh, disc brakes. They use them on motorcycles, so that's what
I need! I'll never buy a bike without them things!"

We're supposed to be better than that. We should consider both
advantages and disadvantages. It happens to be my judgment that for
almost all road cyclists, the disadvantages outweigh the advantages.
Almost everyone would be better off with more normal brakes.

What is "almost everyone" if it is not the set of people minus a small
subset? Did I not identify a subset as "a person [who] wants to use
wheels with CFRP rims"?

Surely everyone minus a small subset equals almost everyone?

If it was because I elaborated on Jay's comment that made you think
something else, you're reading too much between the lines.

I was not trying to disagree with you, James. I don't see anything that
I wrote above that should be interpreted as disagreement with you.

I'm saying that yes, discs have certain advantages. You described one.
I'm saying that we should also discuss disadvantages. I hope that's clear.


It seemed to me that both advantages and disadvantages are being
discussed throughout this thread. Why my elaboration of an advantage
should elicit a "We're supposed to be better than that." reply is beyond me.

--
JS

On Thursday, September 28, 2017 at 3:10:28 PM UTC-7, wrote:
On Thursday, September 28, 2017 at 7:15:06 AM UTC-7, jbeattie wrote:
On Wednesday, September 27, 2017 at 3:18:31 PM UTC-7, Doug Landau wrote:
On Tuesday, September 26, 2017 at 7:57:06 PM UTC-7, Frank Krygowski wrote:
On 9/26/2017 8:34 PM, John B. wrote:
On Tue, 26 Sep 2017 07:18:28 -0700 (PDT), jbeattie wrote:

"Braking is also more rapid and positive with a well adjusted disc."

I would really like to see the dynamics of that statement explained as
during the 20 years or so that I worked on aircraft it was always
explained to us that maximum braking force is generated just before
the tire starts to skid which I have always assumed applied to any
rubber tired wheel and thus any brake that could actual stop the wheel
from turning must be capable of generating maximum braking force.

I've thought a bit about the descriptions of brake behavior. What you
say about maximum deceleration occurring very near skidding is certainly
correct. But what about statements like Jay's "rapid and positive," or
others' descriptions of "progressive" or "controllable" and the like?

In a straight line. He is still only considering the situation of moving in a straight line. While turning, maximum braking will occur at a lower point than the coefficient of friction of the tires, and the result of exceeding the available traction will be a spin and fall, rather than a skid.

I was thinking about wet braking. Discs engage faster and with more braking force than rim brakes because you're not drying the rims, and the pad force is higher in discs. In dry weather, I'd only bother with a disc if I had CF rims or was mountain biking or doing exceedingly steep descents on a gravel bike. My hands did get tired with rim brakes on a recent gravel descent.

-- Jay Beattie.

Jay, I haven't actually had that problem when fording creeks. So I find it hard to believe that people actually have a problem with it. You don't have to "dry" the rim. You only have to cut through the surface layer on a very small section. Once you're through the layer the shoes push the water out of the way.

There is definitely a lag between lever force and braking with rim brakes in wet weather -- and that lovely grinding sound as grit is pressed against the rim. There is a little lag time with cable discs, too, but its much shorter, IMO.

It's not like I can't stop with rim brakes in the rain. I can, but I stop better with discs and don't get the rim grinding -- and to the extent I grind a rotor, I can replace that for few bucks in two minutes with my TORX head driver bit. Discs are just better for rain riding.

I hated my rear cable disc last night because it was dragging. The return spring is weak, and I have a new brake on the way. Also, the wheel got skewed in the dropout because the QR didn't hold it. It's some Chinese POS QR with the plastic cam piece. That's going in the trash. It totally sucks to climb some 15% pitch with a dragging brake. Basically this climb in reverse in the dark after some drinks at a friends. https://www.youtube.com/watch?v=ATARc0TDdXg (you can see my office tower at 4:06 from the top of a sled hill). I do not know how Joerg rides after drinking.

-- Jay Beattie.

On 9/28/2017 6:33 PM, James wrote:
On 28/09/17 13:54, Frank Krygowski wrote:
On 9/27/2017 8:25 PM, James wrote:
On 27/09/17 04:09, Frank Krygowski wrote:
On 9/26/2017 4:38 AM, James wrote:
On 26/09/17 13:06, Frank Krygowski wrote:
On 9/25/2017 6:00 PM, jbeattie wrote:
Â*People are willing to accept the weight and aerodynamic penalty
with
discs, apparently on the belief that ordinary rim brakes are
inadequate or because they want to use CF wheels. Who knows.

Many people are willing to accept anything that's in fashion in their
own little world. Fashion is amazingly powerful, and doesn't need to
make any particular sense.

At least we can claim that disc brakes are marginally more useful
than
tattoos.


If a person wants to use wheels with CFRP rims, a bike with disc
brakes makes sense.

CFRP rims with rim brakes usually work ok in dry conditions provided
the correct brake blocks are used.Â* Some CFRP rims can be damaged if
the wrong pads are used, and some have been damaged even with the
"correct" pads.

But in wet conditions, the braking performance is generally very much
worse.

Disc brakes solve those problems, and allow rim manufacturers to save
more grams because there's no need for a braking surface.

I'm not saying there are never benefits to disc brakes, and I don't
think anyone else is saying that.

I would never tell Jay he shouldn't use discs; his commuting regimen in
hilly, rainy Portland is perfect for them.

So yes, discs have some advantages. They also have some disadvantages,
and those disadvantages become known only through discussions something
like this one. Advertisers are certainly not going to spend much time
listing the disadvantages.

And the typical consumer isn't going to think about these things at
all,
beyond "Oooh, disc brakes. They use them on motorcycles, so that's what
I need! I'll never buy a bike without them things!"

We're supposed to be better than that. We should consider both
advantages and disadvantages. It happens to be my judgment that for
almost all road cyclists, the disadvantages outweigh the advantages.
Almost everyone would be better off with more normal brakes.

What is "almost everyone" if it is not the set of people minus a small
subset?Â* Did I not identify a subset as "a person [who] wants to use
wheels with CFRP rims"?

Surely everyone minus a small subset equals almost everyone?

If it was because I elaborated on Jay's comment that made you think
something else, you're reading too much between the lines.

I was not trying to disagree with you, James. I don't see anything that
I wrote above that should be interpreted as disagreement with you.

I'm saying that yes, discs have certain advantages. You described one.
I'm saying that we should also discuss disadvantages. I hope that's
clear.


It seemed to me that both advantages and disadvantages are being
discussed throughout this thread.Â* Why my elaboration of an advantage
should elicit a "We're supposed to be better than that." reply is beyond
me.

Ah, well.

--
- Frank Krygowski

On Thu, 28 Sep 2017 07:15:03 -0700 (PDT), jbeattie
wrote:

On Wednesday, September 27, 2017 at 3:18:31 PM UTC-7, Doug Landau wrote:
On Tuesday, September 26, 2017 at 7:57:06 PM UTC-7, Frank Krygowski wrote:
On 9/26/2017 8:34 PM, John B. wrote:
On Tue, 26 Sep 2017 07:18:28 -0700 (PDT), jbeattie wrote:

"Braking is also more rapid and positive with a well adjusted disc."

I would really like to see the dynamics of that statement explained as
during the 20 years or so that I worked on aircraft it was always
explained to us that maximum braking force is generated just before
the tire starts to skid which I have always assumed applied to any
rubber tired wheel and thus any brake that could actual stop the wheel
from turning must be capable of generating maximum braking force.

I've thought a bit about the descriptions of brake behavior. What you
say about maximum deceleration occurring very near skidding is certainly
correct. But what about statements like Jay's "rapid and positive," or
others' descriptions of "progressive" or "controllable" and the like?

In a straight line. He is still only considering the situation of moving in a straight line. While turning, maximum braking will occur at a lower point than the coefficient of friction of the tires, and the result of exceeding the available traction will be a spin and fall, rather than a skid.

I was thinking about wet braking. Discs engage faster and with more braking force than rim brakes because you're not drying the rims, and the pad force is higher in discs. In dry weather, I'd only bother with a disc if I had CF rims or was mountain biking or doing exceedingly steep descents on a gravel bike. My hands did get tired with rim brakes on a recent gravel descent.

-- Jay Beattie.

:-) Yes, the "pad force" is higher with discs. But after all, due to
the limited radial arm of the small disk, it has to be in order to
generate the same braking force as the much larger rim :-)
--
Cheers,

John B.