The death of rim brakes?

James wrote:
On 17/3/19 2:56 am, Ralph Barone wrote:

I missed commenting to John earlier. Your visualization of the problem
isn't quite right. With rim brakes, the spokes do not see any braking
forces, since the brakes sit between the spokes and the tire.

The spokes may not see any torque between the hub and rim, but are
certainly forces due to braking that the spokes see.


Now that I think about it some more, yes, there should be increased tension
on the rear facing spokes and decreased tension on the forward facing
spokes under rim braking. However, under disc braking, there should be an
additional torque which should increase tension on all spokes where the
head leads the nipple and decreased tension on all spokes where the nipple
leads the head (I'm sure there's a technical term for it, but it currently
escapes my mind).

I imagine that these "torsionally derived tensions" in disc applications
are greater than the spoke tension changes with rim braking.

On Sat, 16 Mar 2019 15:56:04 +0000 (UTC), Ralph Barone
wrote:

James wrote:
On 16/3/19 10:32 am, John B. Slocomb wrote:


It comes to mind that as the braking resistance is applied at the
contact of the tire and the road and that the resistance is applied to
the wheel hub that a much stronger disc brake wheel would be required
than when using a rim brake as the ratio between the disc brake disc
and the contact with the road is approximately 26.5"/7.5" (average 2
sizes of disc rotor) = about 3.5 ratio while a rim brake is only about
an inch and a half difference so say 26.5/23.5=1.1 ratio. Based on
braking forces it would appear that a disc brake wheel would have to
be roughly 3 times stronger than a rim brake wheel.

36 spoke, cross three, wheels anyone?

But of course an ATB is already so heavy that the addition of strong
wheels is rather a matter of bringing coals to Newcastle.


Well, you don't build a disc brake wheel with radial spokes.



I missed commenting to John earlier. Your visualization of the problem
isn't quite right. With rim brakes, the spokes do not see any braking
forces, since the brakes sit between the spokes and the tire.

I see. True the spokes see no breaking force but they do see a force
simply because they connect the rim to the bicycle and the bicycle
(and rider) represent a certain amount of inertia which has to be
overcome.

No matter
what size of disc brake you have, the spoke forces are the same, since the
braking force is applied to the hub, which then transfers it through the
spokes to the rim/tire. In the limit, the hub is stationary and the wheel
is sliding. In this case, the size of the disc determines how much
tangential force is applied to the disc, but the force on the spokes is
determined by the number of spokes, the lacing pattern and the hub
diameter.

Exactly. As I said, 36 spokes laced "cross three" :-)

--
Cheers,
John B.

On Sun, 17 Mar 2019 08:30:51 +1100, James
wrote:

On 16/3/19 7:38 pm, John B. Slocomb wrote:
On Sat, 16 Mar 2019 18:57:21 +1100, James
wrote:

On 16/3/19 10:32 am, John B. Slocomb wrote:


It comes to mind that as the braking resistance is applied at the
contact of the tire and the road and that the resistance is applied to
the wheel hub that a much stronger disc brake wheel would be required
than when using a rim brake as the ratio between the disc brake disc
and the contact with the road is approximately 26.5"/7.5" (average 2
sizes of disc rotor) = about 3.5 ratio while a rim brake is only about
an inch and a half difference so say 26.5/23.5=1.1 ratio. Based on
braking forces it would appear that a disc brake wheel would have to
be roughly 3 times stronger than a rim brake wheel.

36 spoke, cross three, wheels anyone?

But of course an ATB is already so heavy that the addition of strong
wheels is rather a matter of bringing coals to Newcastle.


Well, you don't build a disc brake wheel with radial spokes.

But they do built a rim brake wheel with radial spokes }-)

Yes, I use some I built. It's mostly a fashion thing. The weight
reduction by shorter spokes isn't worth worrying about.

But as the "weight weenies" say, every little bit helps. Thus the
titanium seat bolt clamp bolts :-)

In most cases a regular 3x spoke wheel is sufficient to transfer brake
forces from the hub to the rim.

Imagine the possible force on spokes possible from a 28 tooth chain ring
to a 34 tooth rear sprocket?


I think that if I were riding around in the mud and mire I probably
would want discs but I don't do that. Anywhere that I want to go has
paved roads leading to it.

I find it rather revealing that in 1880 the League of American
Wheelmen, a bicycle advocate group, was formed and one of the first
things that they lobbied for was smooth roads. Now that smooth roads,
in the U.S. at least, probably make up the majority of the roads
people have discovered riding out in the bush where there hardly
aren't any roads at all.


Where I live there are hundreds of kms of gravel roads that are too
rough for my road bike (I've tried). Where as my options are limited by
bitumen only roads. Only the main connecting roads are bitumen, and
they are high speed roads where drivers dislike passing cyclists safely.

I think that people have realised that there are many unmade roads to
explore, and there are few cars on them to worry about.

--
Cheers,
John B.

On 3/16/2019 5:50 PM, Ralph Barone wrote:
James wrote:
On 17/3/19 2:56 am, Ralph Barone wrote:

I missed commenting to John earlier. Your visualization of the problem
isn't quite right. With rim brakes, the spokes do not see any braking
forces, since the brakes sit between the spokes and the tire.

The spokes may not see any torque between the hub and rim, but are
certainly forces due to braking that the spokes see.


Now that I think about it some more, yes, there should be increased tension
on the rear facing spokes and decreased tension on the forward facing
spokes under rim braking.

I suspect it would instead be very much like the situation of a bike
wheel supporting a vertical load. In that case, there's negligible
increase in tension as a reaction to the load. Instead, there's a
decrease in tension in the spokes between the hub and the ground.

For a wheel with applied vertical load plus rim braking, I think the
spokes pointed forward and downward from the hub would see a decrease in
tension. The others would see no significant increase. Check out a free
body diagram of the wheel, and a FBD of the hub.

However, under disc braking, there should be an
additional torque which should increase tension on all spokes where the
head leads the nipple and decreased tension on all spokes where the nipple
leads the head (I'm sure there's a technical term for it, but it currently
escapes my mind).

I imagine that these "torsionally derived tensions" in disc applications
are greater than the spoke tension changes with rim braking.

Perhaps- depending on how hard the brakes are applied. I think a lot of
folks visualize extreme applications of brakes. But I know almost all my
brake applications are very gentle. It just makes no sense to be braking
hard very often, and wasting all that energy. I'm pretty sure most
people plan ahead enough to minimize their braking.

--
- Frank Krygowski

On Sat, 16 Mar 2019 23:04:02 -0400, Frank Krygowski
wrote:

On 3/16/2019 5:50 PM, Ralph Barone wrote:
James wrote:
On 17/3/19 2:56 am, Ralph Barone wrote:

I missed commenting to John earlier. Your visualization of the problem
isn't quite right. With rim brakes, the spokes do not see any braking
forces, since the brakes sit between the spokes and the tire.

The spokes may not see any torque between the hub and rim, but are
certainly forces due to braking that the spokes see.


Now that I think about it some more, yes, there should be increased tension
on the rear facing spokes and decreased tension on the forward facing
spokes under rim braking.

I suspect it would instead be very much like the situation of a bike
wheel supporting a vertical load. In that case, there's negligible
increase in tension as a reaction to the load. Instead, there's a
decrease in tension in the spokes between the hub and the ground.

For a wheel with applied vertical load plus rim braking, I think the
spokes pointed forward and downward from the hub would see a decrease in
tension. The others would see no significant increase. Check out a free
body diagram of the wheel, and a FBD of the hub.

Certainly true for crossed spokes but what about radial spokes, which
are now common in front wheels where, likely, the greatest braking
force is imposed?

It might be noted that disc brakes impose enough force against the
fork to, possibly, cause the axle to move downward in the drop-outs,
thus solid axles in some modern bicycles.


However, under disc braking, there should be an
additional torque which should increase tension on all spokes where the
head leads the nipple and decreased tension on all spokes where the nipple
leads the head (I'm sure there's a technical term for it, but it currently
escapes my mind).

I imagine that these "torsionally derived tensions" in disc applications
are greater than the spoke tension changes with rim braking.

Perhaps- depending on how hard the brakes are applied. I think a lot of
folks visualize extreme applications of brakes. But I know almost all my
brake applications are very gentle. It just makes no sense to be braking
hard very often, and wasting all that energy. I'm pretty sure most
people plan ahead enough to minimize their braking.

--
Cheers,
John B.

On Saturday, March 16, 2019 at 11:37:49 PM UTC-4, John B. Slocomb wrote:
On Sat, 16 Mar 2019 23:04:02 -0400, Frank Krygowski
wrote:

On 3/16/2019 5:50 PM, Ralph Barone wrote:
James wrote:
On 17/3/19 2:56 am, Ralph Barone wrote:

I missed commenting to John earlier. Your visualization of the problem
isn't quite right. With rim brakes, the spokes do not see any braking
forces, since the brakes sit between the spokes and the tire.

The spokes may not see any torque between the hub and rim, but are
certainly forces due to braking that the spokes see.


Now that I think about it some more, yes, there should be increased tension
on the rear facing spokes and decreased tension on the forward facing
spokes under rim braking.

I suspect it would instead be very much like the situation of a bike
wheel supporting a vertical load. In that case, there's negligible
increase in tension as a reaction to the load. Instead, there's a
decrease in tension in the spokes between the hub and the ground.

For a wheel with applied vertical load plus rim braking, I think the
spokes pointed forward and downward from the hub would see a decrease in
tension. The others would see no significant increase. Check out a free
body diagram of the wheel, and a FBD of the hub.

Certainly true for crossed spokes but what about radial spokes, which
are now common in front wheels where, likely, the greatest braking
force is imposed?

It might be noted that disc brakes impose enough force against the
fork to, possibly, cause the axle to move downward in the drop-outs,
thus solid axles in some modern bicycles.


However, under disc braking, there should be an
additional torque which should increase tension on all spokes where the
head leads the nipple and decreased tension on all spokes where the nipple
leads the head (I'm sure there's a technical term for it, but it currently
escapes my mind).

I imagine that these "torsionally derived tensions" in disc applications
are greater than the spoke tension changes with rim braking.

Perhaps- depending on how hard the brakes are applied. I think a lot of
folks visualize extreme applications of brakes. But I know almost all my
brake applications are very gentle. It just makes no sense to be braking
hard very often, and wasting all that energy. I'm pretty sure most
people plan ahead enough to minimize their braking.

--
Cheers,
John B.

Radial Spokes on disc equipped front wheels? Sounds like a recipe for broken spokes. Then again, if the disc brake is concentrating the applied braking force close to the hub perhaps a radial spoke front wheel isn't as prone to spoke breakage as it would be if the braking force was at the rim? I'm thinking about the torque at both locations.

It also seems to me that with through axles (iiuc) that a bicyclist LOSES the advantage of a quick release wheel. I know that those damn lawyer lips are a pain in the butt most times and largely negate the reason to have a quick release in the first place.

Cheers

On 2019-03-15 07:08, wrote:
On Thursday, March 14, 2019 at 6:36:52 PM UTC-7, James wrote:
On 15/3/19 2:17 am, Frank Krygowski wrote:
On 3/13/2019 6:32 PM, Joerg wrote:
On 2019-03-12 11:13, AMuzi wrote:

How many new bicycles have drum brakes? Vanishingly few.


This was just meant as an example. Bicycles have largely
remained in the stone age, like chuck wagons where a chunk of
wood pressed against the steel ring of the wheels to brake. So
bicycles kind of skipped a technology.

Bikes didn't skip drum brake technology because bikes are
primitive. Only a very few bikes adopted drum brakes because that
technology wasn't optimum for bikes.

It's simplistic at best to pretend what's best for one
application is best for all applications. Every design choice
comes with benefits and detriments, and those are not the same
for a 4000 pound car as for a 20 pound bike.

Bicycle rim brakes have worked fine for over 99.999% users for
the past 100+ years. When mountain bikes came into fashion, some
off-roaders found a different set of benefits vs. detriments, and
discs made sense for them. But then fashion and marketing took
over, pushing discs toward road bikes.

Yes, we'll get a few testimonials here claiming discs are
"better." We get very few details on benefits vs. detriments.



For a while, the trend for road bikes was very narrow tyres pumped
up to very high pressure. 18 mm of tyre is pretty skinny.

Gradually the tyre width had become standard at 23 mm for road
bikes.

Now there is an emerging trend to ride wider tyres, with some
claiming much wider tyres are not only as fast but faster! I
suspect there is a diminishing return with wind resistance.

Now I use a 25 mm rear tyre (that measures 27 mm), and to remove
the wheel I must release the brake lever (Campagnolo) or deflate
the tyre. With a 23 mm tyre I don't need to do that. With a disc
brake I don't need to fiddle with the brakes regardless of tyre
width. That's a benefit.

In fact sometimes when you go to shove a wheel in with rim brakes
and centre or dual pivot callipers, you can catch the calliper and
move it from centred. Then you have to fix that or have rubbing
brakes. That doesn't happen with discs.

It is possible with hydraulic disc callipers to squeeze the brake
lever while the wheel is out, and then have trouble moving the pads
apart again to insert the wheel. That's a detriment, but doesn't
affect cable actuated disc brake callipers.

Hydraulic disc callipers are self adjusting like car hydraulic
disc callipers. Cable actuated disc callipers are not. Benefit
and detriment.

Hydraulic disc systems sometimes need bleeding. This requires
either a visit to a shop or a bit more kit ($30 - $50) for the home
maintenance person. Detriment. Probably not good if you are out
on a tour. Cables are probably more reliable. Cable operated discs
work fine, and there are also cable/hydraulic systems, where the
calliper is hydraulic and self adjusting, and actuated via a
cable.

Disc brake modulation is generally better. That is you can hold
the point of not quite skidding more easily. Benefit.

Disc brakes tend to work better in wet weather, or IOW, work the
same regardless of wet weather. Rim brakes rarely work as well
when the rims are wet.

Rim brakes on carbon fibre rims has never been a happy marriage,
but with disc brakes that problem is eliminated. Thus aerodynamic,
strong, stiff, light weight rims are now easier to manufacture and
use - made of carbon fibre.

Rim brakes do erode rims. Disc brakes do not. I guess the disc
rotor will wear out, but I'd rather replace a rotor than a rim.

It seems to me that many people try disc brakes and find few
drawbacks. That's just my opinion, unsubstantiated by statistics.

Are rim brakes good enough? Sure! They have been for a long time.
Are disc brakes better? Yes I think so. Not outstandingly, but
better. I'm not about to have my road bike modified to take disc
brakes, and I wouldn't let the choice of brakes on a new bike
dictate what I bought. YMMV.

-- JS
I took out the Colnago yesterday since I've been riding the cheaper
bikes with all the rain this year. I just put on a set of 25 mm
tubeless carbon rims with the Continental GP5000TL tires. Old person
with less than 400 miles and very little climbing so far this years
means that I'm am slower than frozen snot.

But I waited at the top for the group who started 5 minutes after me.
They caught me at the top. Rolling down the other side I could COAST
faster than the others could pedal. I started as tail end charley
because I assumed they would be a fast downhill as up. But I kept
overrunning the group and there was one out in front with a new
custom steel bike with a new 11 speed Ultegra. I accelerated to catch
him and then had to actually put the brakes on to keep from passing
him FAST. And then I was 4 bike lengths behind him and coasting most
of the rest of the way. When the road flattened out I had to only
pedal half the time. As soon as the road went up even a little I was
working a whole lot harder than he was.


How much do you weigh? I am around 220lbs and that, combined with a
steel frame, full tool set and other stuff in the panniers, makes me
pass almost everyone else on the downhill. On the uphill, not so much ...

Disc and rim brakes don't make a difference in that respect IME.

--
Regards, Joerg

http://www.analogconsultants.com/

On 2019-03-14 18:36, James wrote:
On 15/3/19 2:17 am, Frank Krygowski wrote:
On 3/13/2019 6:32 PM, Joerg wrote:
On 2019-03-12 11:13, AMuzi wrote:

How many new bicycles have drum brakes? Vanishingly few.


This was just meant as an example. Bicycles have largely remained in
the stone age, like chuck wagons where a chunk of wood pressed
against the steel ring of the wheels to brake. So bicycles kind of
skipped a technology.

Bikes didn't skip drum brake technology because bikes are primitive.
Only a very few bikes adopted drum brakes because that technology
wasn't optimum for bikes.

It's simplistic at best to pretend what's best for one application is
best for all applications. Every design choice comes with benefits and
detriments, and those are not the same for a 4000 pound car as for a
20 pound bike.

Bicycle rim brakes have worked fine for over 99.999% users for the
past 100+ years. When mountain bikes came into fashion, some
off-roaders found a different set of benefits vs. detriments, and
discs made sense for them. But then fashion and marketing took over,
pushing discs toward road bikes.

Yes, we'll get a few testimonials here claiming discs are "better." We
get very few details on benefits vs. detriments.



For a while, the trend for road bikes was very narrow tyres pumped up to
very high pressure. 18 mm of tyre is pretty skinny.

Gradually the tyre width had become standard at 23 mm for road bikes.

Now there is an emerging trend to ride wider tyres, with some claiming
much wider tyres are not only as fast but faster! I suspect there is a
diminishing return with wind resistance.


I think the common sweet spot concensus is 25mm which is what I am
riding right now. Though I'd rather have 32mm in back for CX capability
but unfortunately the frame isn't built for that.


Now I use a 25 mm rear tyre (that measures 27 mm), and to remove the
wheel I must release the brake lever (Campagnolo) or deflate the tyre.
With a 23 mm tyre I don't need to do that. With a disc brake I don't
need to fiddle with the brakes regardless of tyre width. That's a benefit.


That I don't understand. Even the early 80's Shimano 600 set on my road
bike has little release handles on each caliper to get out a 25mm+ wheel
with lots of room to spare.


In fact sometimes when you go to shove a wheel in with rim brakes and
centre or dual pivot callipers, you can catch the calliper and move it
from centred. Then you have to fix that or have rubbing brakes. That
doesn't happen with discs.


Though a disc does get bent easily and you have to pay more attention
when re-installing a wheel. Fixing is easy as well as long as you do not
touch the disc with bare hands.


It is possible with hydraulic disc callipers to squeeze the brake lever
while the wheel is out, and then have trouble moving the pads apart
again to insert the wheel.


This falls under the category "Don't do that!" :-)


... That's a detriment, but doesn't affect cable
actuated disc brake callipers.

Hydraulic disc callipers are self adjusting like car hydraulic disc
callipers. ...


Ahm, sort of. The reservoirs are typically a bit small to accommodate
all the wear. I have to top off with DOT-4 at times which is nasty stuff
when it gets onto clothes and things.


Cable actuated disc callipers are not. Benefit and detriment.


Cable calipers are very easy to adjust, just turn a knurled trim knob. A
downside of many is that they only have one moving piston while the
opposite piston is fixed. The rotor flexes to the side every time you
brake. Beats me why they design them that way.


Hydraulic disc systems sometimes need bleeding. This requires either a
visit to a shop or a bit more kit ($30 - $50) for the home maintenance
person. Detriment. Probably not good if you are out on a tour.


IME it's needed once a year at the most. But when it's needed it really
is and not doing it can result in a bad crash.


... Cables
are probably more reliable. Cable operated discs work fine, and there
are also cable/hydraulic systems, where the calliper is hydraulic and
self adjusting, and actuated via a cable.


The cable discs I used just don't have the same kind of stopping power
with modest lever force as hydraulic disc brakes.


Disc brake modulation is generally better. That is you can hold the
point of not quite skidding more easily. Benefit.


I can't confirm that one. My road bike with rim brakes is just as good
in modulating stopping power as my MTB with hydraulic disc brakes.
UNLESS ... it rains a lot. Then it has zero stopping power for a
sometimes gut-churning 1-2sec.


Disc brakes tend to work better in wet weather, or IOW, work the same
regardless of wet weather. Rim brakes rarely work as well when the rims
are wet.

Rim brakes on carbon fibre rims has never been a happy marriage, but
with disc brakes that problem is eliminated. Thus aerodynamic, strong,
stiff, light weight rims are now easier to manufacture and use - made of
carbon fibre.

Rim brakes do erode rims. Disc brakes do not. I guess the disc rotor
will wear out, but I'd rather replace a rotor than a rim.


Plus it's a whole lot cheaper and the replacement job takes a couple of
minutes versus the better part of a Saturday morning.


It seems to me that many people try disc brakes and find few drawbacks.
That's just my opinion, unsubstantiated by statistics.


I was sold on disc brakes after about five seconds of use. When I almost
flew over the handlebar of my new MTB during a test ride in the LBS
parking lot, despite having pulled the handle with just two fingers. The
rear of the MTB actually bucked upwards. It felt like having
power-assist brakes. Woohoo!


Are rim brakes good enough? Sure! They have been for a long time. Are
disc brakes better? Yes I think so. Not outstandingly, but better. I'm
not about to have my road bike modified to take disc brakes, and I
wouldn't let the choice of brakes on a new bike dictate what I bought.
YMMV.


I do. Should I ever need a new road bike it will have discs or I won't buy.

--
Regards, Joerg

http://www.analogconsultants.com/

On Monday, March 18, 2019 at 3:32:49 PM UTC-4, Joerg wrote:
Snipped

I was sold on disc brakes after about five seconds of use. When I almost
flew over the handlebar of my new MTB during a test ride in the LBS
parking lot, despite having pulled the handle with just two fingers. The
rear of the MTB actually bucked upwards. It felt like having
power-assist brakes. Woohoo!

Snipped

I do. Should I ever need a new road bike it will have discs or I won't buy.


--
Regards, Joerg

http://www.analogconsultants.com/

Back around 1982 I bought a Velo Sport Columbus SL Dura Ace AX equipped bicycle and on the ride home was getting squeezed into parked cars by a streetcar because the road was narrowing quite a bit. I hit the brakes and the rear wheel lifted quite a bit before I released the front brake lever and hit the brakes again. That was with the AX caliper brake. I've always loved the braking of those brakes.

Cheers

On 2019-03-18 13:57, Sir Ridesalot wrote:
On Monday, March 18, 2019 at 3:32:49 PM UTC-4, Joerg wrote: Snipped

I was sold on disc brakes after about five seconds of use. When I
almost flew over the handlebar of my new MTB during a test ride in
the LBS parking lot, despite having pulled the handle with just two
fingers. The rear of the MTB actually bucked upwards. It felt like
having power-assist brakes. Woohoo!

Snipped

I do. Should I ever need a new road bike it will have discs or I
won't buy.


-- Regards, Joerg

http://www.analogconsultants.com/

Back around 1982 I bought a Velo Sport Columbus SL Dura Ace AX
equipped bicycle and on the ride home was getting squeezed into
parked cars by a streetcar because the road was narrowing quite a
bit. I hit the brakes and the rear wheel lifted quite a bit before I
released the front brake lever and hit the brakes again. That was
with the AX caliper brake. I've always loved the braking of those
brakes.


Now try the same on a rainy day. Yeah, a rim brake can still lift the
rear but it could be 1-2sec too late. I don't want that.

--
Regards, Joerg

http://www.analogconsultants.com/