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Why do some forks and frames have brake rotor size limits?



 
 
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  #271  
Old November 1st 17, 08:35 PM posted to rec.bicycles.tech
Joerg[_2_]
external usenet poster
 
Posts: 6,016
Default Why do some forks and frames have brake rotor size limits?

On 2017-10-31 07:05, wrote:
On Monday, October 30, 2017 at 1:54:27 PM UTC-7, Joerg wrote:
On 2017-10-30 12:35,
wrote:
On Monday, October 30, 2017 at 9:39:55 AM UTC-7, Joerg wrote:
On 2017-10-29 12:57,
wrote:
On Sunday, October 29, 2017 at 10:02:12 AM UTC-7, Joerg
wrote:
On 2017-10-29 09:45,
wrote:
On Saturday, October 28, 2017 at 8:09:18 AM UTC-7, Joerg
wrote:

And grandpa has driven his cars without safety belts
yet survived ...

For people who do not shy away from unpaved roads or
use a lot of singletrack and ride in the rain there is
a much more extreme issue: Wet mud.

There is NO brake the is proof against wet mud. In fact
it is perhaps worse on a disk since the additional
pressure of the pads can turn the silicon present in most
muds into cutting instruments that on rim brakes cuts
into the rubber show rather than the hard and thin disk
pad.


Actually, no. I've had mud literally dripping from the
calipers which had become barely recognizable brownish
blobs. The only thing that happens is that they make an
awful grinding noise just like muddy rim brakes do. With
the two major differences that they still come on full
force immediately and that this grinding does not eat up
aluminum. Aluminum as one of the braking surfaces plain
does not make any sense, certainly not in a muddy
environment.

A downside of bicycle disc brakes is that in contrast to
most motor vehicles the rotors have "vent holes" and weight
weenie spiders. This results in rather fast heat-up and in
"brake mousse" when you plow through thick vegetation on an
overgrown trail. Mashed star-thistle and other weeds get
shredded and a sort of pulp develops which cakes up in the
holes of the rotor. It doesn't diminish the brake force but
lets of a bad stench. One of the reasons why I carry a
Swiss Army knife in a pocket. Not in a pannier, so I can
whip it out in seconds. This also helps in poking out the
giant mud clump that forms behind the BB and can prevent
the rear wheel from turning.

Joerg - that additional noise is wear.


Sure. However, the rotors last thousands of miles, cost around
$20 and take only minutes to change. The pads cost $2/pair for
ceramic-based material (like motorcycles have) and last around
1000mi depending on turf and weather. That is way more hassle
than with a motor vehicle but way less hassle than swapping out
a shot rim.

I started riding again in fall 2013, using an older model MTB
with almost zero miles on it. By the end of 2013 it had around
1000mi on it and the front rim looks horrible.

The problem in our area is this: Mud contains granules of
decomposed granite. Rubber pads need water diverter grooves and
the granules lodge in these grooves. They also pierce the
rubber itself and lodge in there. When pulling the lever that
lets of a horrid grinding noise. Coming down a hill you have to
keep the brake engaged and you can literally hear the rim being
tortured all the way to the bottom of the hill. On flat
surfaces you have to stop and pry out the granules. On a rainy
day that means stopping every few miles. I stand by my opinion
that rim brakes are inadequate for any serious MTB riding.

Well, perhaps it was from older parts but I saw a significant
number of MTB riders walking their bikes back off of hills. Those
were the older cable pull brakes so that might have been when
they were still developing the proper compounds.

https://www.youtube.com/watch?v=Wdb7KEc7xJI


Wow, 2x the stopping distance for the rim brakes. I wouldn't have
imagined it could be that much worse.


This is comparing an 11 speed Ghost with an aluminum el-cheapo
Raleigh. This was a highly unfair test to begin with: On the
climbing test the Raleigh had an eight speed compact that simply
didn't have the correct gearing. And the bicycle size and set-up
was entirely wrong.

On the braking test it was hydraulic disks against what appeared
to the the old-fashioned long throw brakes. There was so much
bend in the brakes that you could bottom out the lever.


I don't think he bottomed out the levers.


On the TT again the problem was that there simply wasn't the
proper gearing. And since the Raleigh wasn't sized correctly it
was nearly impossible to get into an aero position.

Personally in the brake test I believe my Skeleton brakes would
have finished not exactly with the disks but really close. There
is no flex to speak of in my brakes and while I think I could
lock the front wheel and allow the rear wheel to rise off of the
ground there is absolutely no day I would do such a thing.

My bikes are set up similar seating position to the Raleigh. But
I could merely change the stem to gain a position such as the
Ghost. I personally don't give much credit to the aerodynamics of
a frame.


Gearing and such are a different matter but brakes are
safety-relevant. I wouldn't want to compromise there.


Think about this Joerg - if he didn't bottom out the lever wouldn't
he pull harder?



A lever is never supposed to bottom out before the brake force on
respective wheel is maxed. If it did then he'd have faulty brakes and I
am sure he'd not have posted this. The guys look like serious cyclists
who know this.


... As for your opinions on safety I can understand your
position after seeing how much weight you carry.


The difference isn't that large. 20-30lbs in extra bike equipment, water
and whatnot. It's peanuts.

--
Regards, Joerg

http://www.analogconsultants.com/
Ads
  #272  
Old November 1st 17, 08:36 PM posted to rec.bicycles.tech
Joerg[_2_]
external usenet poster
 
Posts: 6,016
Default Why do some forks and frames have brake rotor size limits?

On 2017-10-31 07:23, wrote:
On Monday, October 30, 2017 at 3:40:30 PM UTC-7, Joerg wrote:
On 2017-10-30 15:10, Doug Landau wrote:
On Monday, October 30, 2017 at 2:16:43 PM UTC-7, Joerg wrote:
On 2017-10-30 14:04, Doug Landau wrote:
On Monday, October 30, 2017 at 1:58:51 PM UTC-7, Joerg wrote:
On 2017-10-30 13:17, Doug Landau wrote:
On Monday, October 30, 2017 at 9:39:55 AM UTC-7, Joerg
wrote:
On 2017-10-29 12:57,
wrote:
On Sunday, October 29, 2017 at 10:02:12 AM UTC-7, Joerg
wrote:
On 2017-10-29 09:45,
wrote:
On Saturday, October 28, 2017 at 8:09:18 AM UTC-7,
Joerg wrote:

And grandpa has driven his cars without safety
belts yet survived ...

For people who do not shy away from unpaved roads
or use a lot of singletrack and ride in the rain
there is a much more extreme issue: Wet mud.

There is NO brake the is proof against wet mud. In
fact it is perhaps worse on a disk since the
additional pressure of the pads can turn the silicon
present in most muds into cutting instruments that on
rim brakes cuts into the rubber show rather than the
hard and thin disk pad.


Actually, no. I've had mud literally dripping from the
calipers which had become barely recognizable brownish
blobs. The only thing that happens is that they make an
awful grinding noise just like muddy rim brakes do.
With the two major differences that they still come on
full force immediately and that this grinding does not
eat up aluminum. Aluminum as one of the braking
surfaces plain does not make any sense, certainly not
in a muddy environment.

A downside of bicycle disc brakes is that in contrast
to most motor vehicles the rotors have "vent holes" and
weight weenie spiders. This results in rather fast
heat-up and in "brake mousse" when you plow through
thick vegetation on an overgrown trail. Mashed
star-thistle and other weeds get shredded and a sort of
pulp develops which cakes up in the holes of the rotor.
It doesn't diminish the brake force but lets of a bad
stench. One of the reasons why I carry a Swiss Army
knife in a pocket. Not in a pannier, so I can whip it
out in seconds. This also helps in poking out the giant
mud clump that forms behind the BB and can prevent the
rear wheel from turning.

Joerg - that additional noise is wear.


Sure. However, the rotors last thousands of miles, cost
around $20 and take only minutes to change. The pads cost
$2/pair for ceramic-based material (like motorcycles have)
and last around 1000mi depending on turf and weather. That
is way more hassle than with a motor vehicle but way less
hassle than swapping out a shot rim.

I started riding again in fall 2013, using an older model
MTB with almost zero miles on it. By the end of 2013 it had
around 1000mi on it and the front rim looks horrible.

The problem in our area is this: Mud contains granules of
decomposed granite. Rubber pads need water diverter grooves
and the granules lodge in these grooves. They also pierce
the rubber itself and lodge in there. When pulling the
lever that lets of a horrid grinding noise. Coming down a
hill you have to keep the brake engaged and you can
literally hear the rim being tortured all the way to the
bottom of the hill. On flat surfaces you have to stop and
pry out the granules. On a rainy day that means stopping
every few miles. I stand by my opinion that rim brakes are
inadequate for any serious MTB riding.

That is the reason to use Kool-stop Salmons. The compound
will not let granules lodge.


So then why does it on my road bike? I use Koolstop up front,
black and salmon. Gravel flakes embed in both when I travel
gravel roads or unpaved sections during soggy weather. Plus
they have grooves which is where they mostly embed:

http://sheldonbrown.com/harris/images/brk14.jpg

-- Regards, Joerg

http://www.analogconsultants.com/

Take a pic next time until then we don't believe it


We? Are you now spokesman for the whole NG? Was there a party
convention with flags and brass band that I missed?

Yes. The election that decided this NG's creation.



Ah, a Chinese style coronation :-)


... Now quit yer
whining and take the goddam pic.



Can you tell me how when the weather is bone dry for months?


... This will be of interest to many
here. The salmon koolstops and their resistance to embedding rocks
are part of the lore of this group, and salmons are popular out of
proportion here.



Maybe there are versions with li'l gremlins in the grooves that shovel
all the dirt out that gets in. Mine don't have those gremlins.


... Now quit complaining about a little effort to do
your part, and show us pics of granules embedded in your salmon.


See above. And it better rain hard soon because my black/salmon
Koolstops are very close to worn down and I certainly will not replace
them with new Koolstops. They wanted $17/pair for the MTB version last
time I looked. Not going to happen. IME Clarks work just as well, last
as long and cost only $4/pair.

In terms of grinding after mud exposure I found there was hardly any
difference between Koolstops and Clarks.


My Campy brake pads appear to be perfectly smooth. Do they need grooves to work properly?


Probably not and I've had pads without. My Koolstops and others that I
have seen do though, for whatever reason.

--
Regards, Joerg

http://www.analogconsultants.com/
  #273  
Old November 1st 17, 09:00 PM posted to rec.bicycles.tech
Frank Krygowski[_4_]
external usenet poster
 
Posts: 10,538
Default Why do some forks and frames have brake rotor size limits?

On 11/1/2017 3:27 PM, Joerg wrote:

With me that happened yesterday. School bus from the other side, driver
backed out of driveway with gusto into the school bus' path, the bus
driver swerved around and into my lane. If I had been lane center I'd be
in the hospital or morgue today.


I don't think I'd have ended up in the hospital just because I rode at
lane center. I know about steering a bike.

--
- Frank Krygowski
  #274  
Old November 1st 17, 09:02 PM posted to rec.bicycles.tech
Joerg[_2_]
external usenet poster
 
Posts: 6,016
Default Why do some forks and frames have brake rotor size limits?

On 2017-11-01 13:00, Frank Krygowski wrote:
On 11/1/2017 3:27 PM, Joerg wrote:

With me that happened yesterday. School bus from the other side,
driver backed out of driveway with gusto into the school bus' path,
the bus driver swerved around and into my lane. If I had been lane
center I'd be in the hospital or morgue today.


I don't think I'd have ended up in the hospital just because I rode at
lane center. I know about steering a bike.


Except when it's too late to get to the side or as in this case off the
road. But I know, you are superman and can easily put on a kilowatt or
two to do this uphill.

--
Regards, Joerg

http://www.analogconsultants.com/
  #275  
Old November 1st 17, 09:32 PM posted to rec.bicycles.tech
[email protected]
external usenet poster
 
Posts: 3,345
Default Why do some forks and frames have brake rotor size limits?

On Wednesday, November 1, 2017 at 12:30:19 PM UTC-7, Joerg wrote:
On 2017-10-31 07:27, wrote:
On Monday, October 30, 2017 at 3:53:11 PM UTC-7, Joerg wrote:
On 2017-10-29 17:09, Frank Krygowski wrote:


[...]

It doesn't pay to be timid. Man up.


Why take the risk when there are alternatives such as this?

https://goo.gl/maps/XJk1gMRC2eA2

A bike lane plus segregated bike path plus bicycle bridge, all
seamlessly connecting to the Folsom bike path system and the
American River bike trail. Plus a lot of parks. That area is a
cyclists paradise. During rush hour it gets quite busy.


So what you're saying is that the percentage of bicyclists deaths can
be changed from nearly nothing to nothing?


It isn't nothing. About one a month in our local paper. However, again,
this is not only about deaths but also serious injury. I personally knew
people who have had that happen, usually by being hit from behind. One
woman wasn't able to ride for years because she ended up underneath a
Ford F-150. Later she never regained her old performance level because
some stuff didn't heal.


I'm certainly not saying that injuries aren't serious. Apparently the pain I presently have in my right arm was caused by that crash I had in July. It didn't bother me until maybe a month ago. Now I have to go through physical therapy to try and quell the pain in my shoulder from a torn ligament.

These sorts of things will always be around. The safest you can ever hope to be is 100 times less safe than you would like to be.

https://www.youtube.com/watch?v=xdWsSB9QGkY

It is somewhat strange to me that no one seems to know why brakes react the way they do. "disk brakes have more modulation". Well that's because a rim brake has more leverage. There is a wider distance between application of the disk brake and the full lock position. I don't have any trouble with brake cables or quick releases making noises.

Looking at the available disk brake videos I have questions as to the techniques they used to make these tests which showed good rim brakes measurably less effective than disks.

https://www.youtube.com/watch?v=xdWsSB9QGkY

https://www.youtube.com/watch?v=uHFSSXOSnxs

I was incorrect about increased drag from disks: the difference was too slight to mention.

https://www.youtube.com/watch?v=HXQuSnKkS-I

My personal experiece with disk brakes is not particularly good. On the heavy Trek HiFi they were very good. On my Redline Cyclocross bike they are all hell and gone too powerful. I installed these when the Shimano cantilever brakes on my Ridley couldn't stop a caterpillar in full flight.

Later I installed TRP 9.0 V-brakes on the Ridley and even though the Ridley is a lot heavier than the Redline, the braking was much more predictable and powerful.






  #277  
Old November 1st 17, 09:39 PM posted to rec.bicycles.tech
[email protected]
external usenet poster
 
Posts: 3,345
Default Why do some forks and frames have brake rotor size limits?

On Wednesday, November 1, 2017 at 12:35:34 PM UTC-7, Joerg wrote:

A lever is never supposed to bottom out before the brake force on
respective wheel is maxed. If it did then he'd have faulty brakes and I
am sure he'd not have posted this. The guys look like serious cyclists
who know this.


How old are you again Joerg? With even the old Campy brakes it was possible to bottom out the levers often without locking the wheels.
  #278  
Old November 1st 17, 09:45 PM posted to rec.bicycles.tech
[email protected]
external usenet poster
 
Posts: 3,345
Default Why do some forks and frames have brake rotor size limits?

On Wednesday, November 1, 2017 at 1:02:54 PM UTC-7, Joerg wrote:
On 2017-11-01 13:00, Frank Krygowski wrote:
On 11/1/2017 3:27 PM, Joerg wrote:

With me that happened yesterday. School bus from the other side,
driver backed out of driveway with gusto into the school bus' path,
the bus driver swerved around and into my lane. If I had been lane
center I'd be in the hospital or morgue today.


I don't think I'd have ended up in the hospital just because I rode at
lane center. I know about steering a bike.


Except when it's too late to get to the side or as in this case off the
road. But I know, you are superman and can easily put on a kilowatt or
two to do this uphill.


I don't ride with the big group anymore. I got tired of every ride being a race.

But I would ride with the moderate group and once in awhile I'd get ticked off at the leaders riding away like that and I would ride up to them on an 8% climb after they had a quarter mile head start. But that was also when I could go from 15 mph to 32 mph to get through lights on busy streets. I think I can only do a sitting sprint to 25 mph or so now. But part of that may be the heavier bike with less aero position.
 




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