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The death of rim brakes?



 
 
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  #31  
Old March 11th 19, 04:53 PM posted to rec.bicycles.tech
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Posts: 1,260
Default The death of rim brakes?

On Sunday, March 10, 2019 at 3:15:24 PM UTC-7, Roger Merriman wrote:
wrote:
On Sunday, March 10, 2019 at 8:34:24 AM UTC-5, wrote:
I keep reading see all the bikes coming out and basically all disc
brakes. I cannot believe rim brakes are going to be gone but maybe I am
just kidding myself. I frankly hate the disc brake look and certainly
for a long time parts will be around but are these rim brakes a dead deal.

Deacon Mark


One of my issues is that I realize we will have rim brake bikes for
awhile but I just hope to keep the nice looks and basic set up. If it is
not broke don't fix the puppy. The one item I have never experience is
the idea on a long descend you can blow a tube. In the flatlands that to
me seems impossible. To blow a tube on a long descend does the speed have
to be really fast like about 40mph or say at 25mph for a long time. The
biggest descend I have done is about 7% grade total for about a mile and
the last say 1/4 mile is got to 9%. I could easily feather the brakes to
avoid heat but maybe my experience is really limited for true mountain
riding. Can you just pull the brakes up pretty good to get to a speed
that is comfortable. In my case this descend got me to about 43mph my top
speed for sure. Had the it been longer I don't know long I could have
continued before I got to damn scared.

Confession of the deacon in lent

Deacon Mark


It’s dragging brakes that does it, not personally had it and have more
experience of seeing lorries with burning brakes for the same reason,
around the area I grew up that has some steep and reasonably long hills, as
kids the main road though the village passing over it via a footbridge
you’d see lorries either in the sandpit on fire or driving past smoking.

I’ve ridden down 0.5-22 mile hills on rims and discs, shorter sharper
braking is generally better, and smooth! Is the trick to being quick and
safe.

Roger Merriman


I agree but I also know that since I had that tire blow completely off of the rim the other day, that you always have to have tires you have complete faith in. There most definitely was some sort of damage to the bead on that tire. Since it really wasn't a tubeless tire we can expect that the loadings on clinches is quite a bit different than on a tubeless but I think that I will have to have a great deal of experience with tubeless tires before I have sufficient faith in them to do the 40-50 mph descents I was doing with clinchers in order to avoid using the brakes and overheating the rims.

As to disks taking over - I don't believe that will ever occur. If for no other reason than rim brakes can be aerodynamically invisible whereas disks cannot be.
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  #32  
Old March 11th 19, 05:01 PM posted to rec.bicycles.tech
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Posts: 1,260
Default The death of rim brakes?

On Sunday, March 10, 2019 at 7:10:21 PM UTC-7, John B. Slocomb wrote:
On Sun, 10 Mar 2019 20:21:40 -0400, Frank Krygowski
wrote:

On 3/10/2019 5:52 PM, wrote:
On Sunday, March 10, 2019 at 8:34:24 AM UTC-5, wrote:
I keep reading see all the bikes coming out and basically all disc brakes. I cannot believe rim brakes are going to be gone but maybe I am just kidding myself. I frankly hate the disc brake look and certainly for a long time parts will be around but are these rim brakes a dead deal.

Deacon Mark

One of my issues is that I realize we will have rim brake bikes for awhile but I just hope to keep the nice looks and basic set up. If it is not broke don't fix the puppy. The one item I have never experience is the idea on a long descend you can blow a tube. In the flatlands that to me seems impossible. To blow a tube on a long descend does the speed have to be really fast like about 40mph or say at 25mph for a long time. The biggest descend I have done is about 7% grade total for about a mile and the last say 1/4 mile is got to 9%. I could easily feather the brakes to avoid heat but maybe my experience is really limited for true mountain riding. Can you just pull the brakes up pretty good to get to a speed that is comfortable. In my case this descend got me to about 43mph my top speed for sure. Had the it been longer I don't know long I could have continued before I got to damn scared.


Long, long ago I read a technical article in some bike magazine. (There
used to be real technical articles in bike magazines.) This one was
about brake energy (or really, power in the engineering sense of work
per unit time) and temperature rise during long descents.

The article explained that the braking power depended on brake force and
speed. For any given hill, you could always use the brakes to go super
slow. Brake force will be high, but speed will be low and power will be
low, leading to less temperature rise.

Alternately, you could descend very fast, braking only lightly or not at
all. Brake force will be low or zero. (There's also more aerodynamic
cooling.) This too will lead to less temperature rise.

The author claimed, using lots of calculations summarized in graphs,
that the greatest temperature rise occurred by using the brakes to keep
the speed about 30 mph or 50 kph.

Trouble is, this is exactly the speed lots of cyclists choose for long
descents. Any slower and they feel like slugs. Any faster and they get
scared.

I blew only one tire on a downhill, on the rear of our tandem, creeping
down a short ( 1/10 mile) steep grade well over 10%. We just rode the
bike to the bottom and I changed the tube. But I can see it would be a
problem if the front tire blew.


Phuket, Thailand has several extremely steep hills on the western side
of the island, steep enough that it is difficult to push a bike up
them.

Out of curiosity I did push the bike up one and coasted down the
eastern side.

Having read all the hoopalla about the rims getting hot and tires
blowing I stopped about half way down and felt the rims... they were,
perhaps, a bit warmer than ambient temperature.

But. As the east side of the hill is a series of "S" turns one can't
just coast down the mountain but must slow down every hundred yards or
so to make the next corner so my braking was a series of pretty hard
brake applications followed by, perhaps, an equal period of coasting.

I have since used that method when descending hills and an occasional
check shows that the rims do not get excessively hot.

--
Cheers,
John B.


John, it has to do with energy dispersal into the rim/tire combination. Steep isn't enough. If you're holding your brakes on to keep a low speed all the way down you don't gain enough energy due to gravitational acceleration to overheat them. But you do wear out the brake pads and rim brake area depth.
  #33  
Old March 11th 19, 05:07 PM posted to rec.bicycles.tech
[email protected]
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Posts: 1,260
Default The death of rim brakes?

On Sunday, March 10, 2019 at 11:10:49 PM UTC-7, Tosspot wrote:
On 3/11/19 1:24 AM, Frank Krygowski wrote:
On 3/10/2019 6:38 PM, wrote:
On Sunday, March 10, 2019 at 4:48:00 PM UTC+1, Sir Ridesalot wrote:
On Sunday, March 10, 2019 at 11:22:10 AM UTC-4, Frank Krygowski wrote:
On 3/10/2019 11:07 AM,
wrote:
On Sunday, March 10, 2019 at 2:34:24 PM UTC+1,
wrote:
I keep reading see all the bikes coming out and basically all disc
brakes. I cannot believe rim brakes are going to be gone but maybe
I am just kidding myself. I frankly hate the disc brake look and
certainly for a long time parts will be around but are these rim
brakes a dead deal.

Deacon Mark

Try to find a ATB without disc brakes. I think that is also gonna
happen with road bikes.

Fashion is weird and powerful.

--
- Frank Krygowski

A few years ago I nearly bought a new disc brake equipped MTB when my
buddy bought his Da Vinci disc brake equipped MTB. However, after
having seen how his bike ate disc brake pads I decide not to replace
my old MTB after all.

I wonder how the cost of replacement disc brake pads over a number of
years compares to the cost of a new rim over those same number of
years? I've never worn out an MTB rim but my buddy was going thorough
a pair of disc brake pads every week or so and that was just from
riding or paved roads or crushed limestone stone dust rail-trails. He
was NOT using the brakes all that much either.

Three bicycle shops here in town could not figure out why his bike
ate pads so fast and that includes* the shop that specializes in
cyclo-cross and MTB trails and has a cyclo-cross team.

Just weird. Rim brakes are fine for a lot of bicyclists yet it seems
that once again a choice will eventually be denied to consumers.

On top of that, if your present bicycle is equipped with racks you'll
most likely have to buy new ones that are disc brake compatible if
you do buy a new bike. Those new racks aren't that cheap either.

Cheers

That is an unusual wear of pads.


I've said this before, but if you're heading out on a long tour with a
disc brake bike, take extra pads. We hosted a guy whose pads suddenly
wore out during a tour, leaving him without brakes until he could find a
bike shop on his route.


I'm wearing out discs (every 4 years) faster than pads. What am I doing
wrong?



I wore out three sets of pads in a number of weeks and they deformed the disks that it was causing accelerated wear. Groves had been burned into the disks. Now these were from 2008 but when I bought the bike it hasn't really been used at all. Perhaps materials have been changed but on my CX bike I have had to change pads in only 300 miles or so. Though there isn't any severe marking on the disks neither have I ridden it all that hard through rather extreme off-road.
  #34  
Old March 11th 19, 06:36 PM posted to rec.bicycles.tech
Mark J.
external usenet poster
 
Posts: 570
Default The death of rim brakes?

On 3/10/2019 8:46 PM, Frank Krygowski wrote:
On 3/10/2019 10:10 PM, John B. Slocomb wrote:
On Sun, 10 Mar 2019 20:21:40 -0400, Frank Krygowski
wrote:

On 3/10/2019 5:52 PM, wrote:
On Sunday, March 10, 2019 at 8:34:24 AM UTC-5,
wrote:
I keep reading see all the bikes coming out and basically all disc
brakes. I cannot believe rim brakes are going to be gone but maybe
I am just kidding myself. I frankly hate the disc brake look and
certainly for a long time parts will be around but are these rim
brakes a dead deal.

Deacon Mark

One of my issues is that I realize we will have rim brake bikes for
awhile but I just hope to keep the nice looks and basic set up. If
it is not broke don't fix the puppy. The one item I have never
experience is the idea on a long descend you can blow a tube. In the
flatlands that to me seems impossible. To blow a tube on a long
descend does the speed have to be really fast like about 40mph or
say at 25mph for a long time. The biggest descend I have done is
about 7% grade total for about a mile and the last say 1/4 mile is
got to 9%. I could easily feather the brakes to avoid heat but maybe
my experience is really limited for true mountain riding. Can you
just pull the brakes up pretty good to get to a speed that is
comfortable. In my case this descend got me to about 43mph my top
speed for sure. Had the it been longer I don't know long I could
have continued before I got to damn scared.

Long, long ago I read a technical article in some bike magazine. (There
used to be real technical articles in bike magazines.) This one was
about brake energy (or really, power in the engineering sense of work
per unit time) and temperature rise during long descents.

The article explained that the braking power depended on brake force and
speed. For any given hill, you could always use the brakes to go super
slow. Brake force will be high, but speed will be low and power will be
low, leading to less temperature rise.

Alternately, you could descend very fast, braking only lightly or not at
all. Brake force will be low or zero. (There's also more aerodynamic
cooling.) This too will lead to less temperature rise.

The author claimed, using lots of calculations summarized in graphs,
that the greatest temperature rise occurred by using the brakes to keep
the speed about 30 mph or 50 kph.

Trouble is, this is exactly the speed lots of cyclists choose for long
descents. Any slower and they feel like slugs. Any faster and they get
scared.

I blew only one tire on a downhill, on the rear of our tandem, creeping
down a short ( 1/10 mile) steep grade well over 10%. We just rode the
bike to the bottom* and I changed the tube. But I can see it would be a
problem if the front tire blew.


Phuket, Thailand has several extremely steep hills on the western side
of the island, steep enough that it is difficult to push a bike up
them.

Out of curiosity I did push the bike up one and coasted down the
eastern side.

Having read all the hoopalla about the rims getting hot and tires
blowing I stopped about half way down and felt the rims... they were,
perhaps, a bit warmer than ambient temperature.

But. As the east side of the hill is a series of "S" turns one can't
just coast down the mountain but must slow down every hundred yards or
so to make the next corner so my braking was a series of pretty hard
brake applications followed by, perhaps, an equal period of coasting.

I have since used that method when descending hills and an occasional
check shows that the rims do not get excessively hot.


Omega and others make temperature indicator dots. They turn black and
stay black when their rated temperature is reached.
https://www.omega.com/pptst/TL-C5_LABELS.html
They're single use products.

Back when Jobst was with us, there was talk of sticking these on some
rims and doing tests, but I don't recall if anyone actually did that, or
what the results were.


Yes, there were tests, I was a test subject. It was in about 1984. I
can't remember for certain, but my guess is the test was sponsored by
Buycycling magazine. I got sent the stick-on temperature indicators.
They were rectangular and had multiple, labeled temp. "windows". When
you reached the indicated temp, the window went (permanently) dark. At
some point I'm sure you sent in results, but I really can't recall that
part.

I'll look in my shop to see if any of the rims (and stickers) are still
around, but I doubt it. In those days we were running 36 spoke rims and
25mm (mis-labeled 1-1/8) Specialized Turbos, and rear rims lasted mostly
a year or two, mostly dying of spoke-hole cracks, and sometimes of
pothole-induced flat spots. Oh to be young and greyhound thin again!

Mark J.


  #35  
Old March 11th 19, 08:30 PM posted to rec.bicycles.tech
JBeattie
external usenet poster
 
Posts: 4,304
Default The death of rim brakes?

On Monday, March 11, 2019 at 10:36:06 AM UTC-7, Mark J. wrote:
On 3/10/2019 8:46 PM, Frank Krygowski wrote:
On 3/10/2019 10:10 PM, John B. Slocomb wrote:
On Sun, 10 Mar 2019 20:21:40 -0400, Frank Krygowski
wrote:

On 3/10/2019 5:52 PM, wrote:
On Sunday, March 10, 2019 at 8:34:24 AM UTC-5,
wrote:
I keep reading see all the bikes coming out and basically all disc
brakes. I cannot believe rim brakes are going to be gone but maybe
I am just kidding myself. I frankly hate the disc brake look and
certainly for a long time parts will be around but are these rim
brakes a dead deal.

Deacon Mark

One of my issues is that I realize we will have rim brake bikes for
awhile but I just hope to keep the nice looks and basic set up. If
it is not broke don't fix the puppy. The one item I have never
experience is the idea on a long descend you can blow a tube. In the
flatlands that to me seems impossible. To blow a tube on a long
descend does the speed have to be really fast like about 40mph or
say at 25mph for a long time. The biggest descend I have done is
about 7% grade total for about a mile and the last say 1/4 mile is
got to 9%. I could easily feather the brakes to avoid heat but maybe
my experience is really limited for true mountain riding. Can you
just pull the brakes up pretty good to get to a speed that is
comfortable. In my case this descend got me to about 43mph my top
speed for sure. Had the it been longer I don't know long I could
have continued before I got to damn scared.

Long, long ago I read a technical article in some bike magazine. (There
used to be real technical articles in bike magazines.) This one was
about brake energy (or really, power in the engineering sense of work
per unit time) and temperature rise during long descents.

The article explained that the braking power depended on brake force and
speed. For any given hill, you could always use the brakes to go super
slow. Brake force will be high, but speed will be low and power will be
low, leading to less temperature rise.

Alternately, you could descend very fast, braking only lightly or not at
all. Brake force will be low or zero. (There's also more aerodynamic
cooling.) This too will lead to less temperature rise.

The author claimed, using lots of calculations summarized in graphs,
that the greatest temperature rise occurred by using the brakes to keep
the speed about 30 mph or 50 kph.

Trouble is, this is exactly the speed lots of cyclists choose for long
descents. Any slower and they feel like slugs. Any faster and they get
scared.

I blew only one tire on a downhill, on the rear of our tandem, creeping
down a short ( 1/10 mile) steep grade well over 10%. We just rode the
bike to the bottom* and I changed the tube. But I can see it would be a
problem if the front tire blew.

Phuket, Thailand has several extremely steep hills on the western side
of the island, steep enough that it is difficult to push a bike up
them.

Out of curiosity I did push the bike up one and coasted down the
eastern side.

Having read all the hoopalla about the rims getting hot and tires
blowing I stopped about half way down and felt the rims... they were,
perhaps, a bit warmer than ambient temperature.

But. As the east side of the hill is a series of "S" turns one can't
just coast down the mountain but must slow down every hundred yards or
so to make the next corner so my braking was a series of pretty hard
brake applications followed by, perhaps, an equal period of coasting.

I have since used that method when descending hills and an occasional
check shows that the rims do not get excessively hot.


Omega and others make temperature indicator dots. They turn black and
stay black when their rated temperature is reached.
https://www.omega.com/pptst/TL-C5_LABELS.html
They're single use products.

Back when Jobst was with us, there was talk of sticking these on some
rims and doing tests, but I don't recall if anyone actually did that, or
what the results were.


Yes, there were tests, I was a test subject. It was in about 1984. I
can't remember for certain, but my guess is the test was sponsored by
Buycycling magazine. I got sent the stick-on temperature indicators.
They were rectangular and had multiple, labeled temp. "windows". When
you reached the indicated temp, the window went (permanently) dark. At
some point I'm sure you sent in results, but I really can't recall that
part.

I'll look in my shop to see if any of the rims (and stickers) are still
around, but I doubt it. In those days we were running 36 spoke rims and
25mm (mis-labeled 1-1/8) Specialized Turbos, and rear rims lasted mostly
a year or two, mostly dying of spoke-hole cracks, and sometimes of
pothole-induced flat spots. Oh to be young and greyhound thin again!



I don't think the selling point for discs is that they prevent your tires from exploding. There has never been a tire-exploding epidemic from over-heating. Like Frank, I blew one tire on a tandem front descending Rocky Point on a hot day. The wet version: https://www.youtube.com/watch?v=-NPqQptjbF0 My wife was on the back yelling at me to slow down, so I complied. This was on a tandem with cantis and no drum or disk brake -- and the rims did get very hot. Discs get super hot on tandems and thus the mega giant 203mm rotors. Tandems are a special case.

Brake fade is a problem with all brakes -- and discs probably get less fade than rim brakes, so heating matters, but the likelihood of blowing a tire off the rim due to over-heating on a road single is pretty remote and not why one would or should buy discs. That's not even something I hear from zealous sales people. The usual pitch is better modulation and stopping in wet weather.

Rim heating was an issue in the tubular days because it didn't take tire-popping heat to soften tubular cement. Having squirming tubulars on a long descent was not uncommon, particularly in hot climates. It was one of the selling points of the new crop of light clinchers in the mid to late '70s. I think discs would be an easy sale to the mountain-climbing clydesdales using CF rims and tubulars.


-- Jay Beattie.
  #36  
Old March 11th 19, 08:40 PM posted to rec.bicycles.tech
Frank Krygowski[_4_]
external usenet poster
 
Posts: 7,804
Default The death of rim brakes?

On 3/11/2019 3:30 PM, jbeattie wrote:
I think discs would be an easy sale to the mountain-climbing clydesdales using CF rims and tubulars.


That's true and very reasonable.

But you're never going to save the bicycling industry with that kind of
reasonable talk!

--
- Frank Krygowski
  #37  
Old March 11th 19, 08:59 PM posted to rec.bicycles.tech
Zen Cycle
external usenet poster
 
Posts: 191
Default The death of rim brakes?

On Sunday, March 10, 2019 at 9:34:24 AM UTC-4, wrote:
I keep reading see all the bikes coming out and basically all disc brakes.. I cannot believe rim brakes are going to be gone but maybe I am just kidding myself. I frankly hate the disc brake look and certainly for a long time parts will be around but are these rim brakes a dead deal.

Deacon Mark


I wouldn't say they are dead, but I can certainly understand how one could interpret that trend. As lou mentioned, they are pretty much on life support for MTBs. Yes, brake parts are available, but you won'd find anything except for walmart special MTBs with rim brakes. I'd say you'll still see rim brakes on road bikes for some time to come, but it probably won't be long before you see some manufacturers making nothing but disc brake road bikes. As of now, very few manufacturers are making rim brake CX bikes, and cannondale has gone so far as to replace the rear brake bridge with a "rear fender mounting bridge" on their CAADX. I don't think you'll have much of a problem buying rim brake road wheels for quite a while though.
  #38  
Old March 11th 19, 09:05 PM posted to rec.bicycles.tech
Zen Cycle
external usenet poster
 
Posts: 191
Default The death of rim brakes?

On Sunday, March 10, 2019 at 8:24:18 PM UTC-4, Frank Krygowski wrote:
On 3/10/2019 6:38 PM, wrote:
On Sunday, March 10, 2019 at 4:48:00 PM UTC+1, Sir Ridesalot wrote:
On Sunday, March 10, 2019 at 11:22:10 AM UTC-4, Frank Krygowski wrote:
On 3/10/2019 11:07 AM,
wrote:
On Sunday, March 10, 2019 at 2:34:24 PM UTC+1, wrote:
I keep reading see all the bikes coming out and basically all disc brakes. I cannot believe rim brakes are going to be gone but maybe I am just kidding myself. I frankly hate the disc brake look and certainly for a long time parts will be around but are these rim brakes a dead deal.

Deacon Mark

Try to find a ATB without disc brakes. I think that is also gonna happen with road bikes.

Fashion is weird and powerful.

--
- Frank Krygowski

A few years ago I nearly bought a new disc brake equipped MTB when my buddy bought his Da Vinci disc brake equipped MTB. However, after having seen how his bike ate disc brake pads I decide not to replace my old MTB after all.

I wonder how the cost of replacement disc brake pads over a number of years compares to the cost of a new rim over those same number of years? I've never worn out an MTB rim but my buddy was going thorough a pair of disc brake pads every week or so and that was just from riding or paved roads or crushed limestone stone dust rail-trails. He was NOT using the brakes all that much either.

Three bicycle shops here in town could not figure out why his bike ate pads so fast and that includes the shop that specializes in cyclo-cross and MTB trails and has a cyclo-cross team.

Just weird. Rim brakes are fine for a lot of bicyclists yet it seems that once again a choice will eventually be denied to consumers.

On top of that, if your present bicycle is equipped with racks you'll most likely have to buy new ones that are disc brake compatible if you do buy a new bike. Those new racks aren't that cheap either.

Cheers


That is an unusual wear of pads.


I've said this before, but if you're heading out on a long tour with a
disc brake bike, take extra pads. We hosted a guy whose pads suddenly
wore out during a tour, leaving him without brakes until he could find a
bike shop on his route.


--
- Frank Krygowski


Many years ago a friend of mine ate through a new set of canti pads on a particularly wet and muddy vermont 50 - a 50 mile mountain bike race. He was quite literally metal on metal by the time he got across the line.
  #39  
Old March 11th 19, 09:12 PM posted to rec.bicycles.tech
Zen Cycle
external usenet poster
 
Posts: 191
Default The death of rim brakes?

On Monday, March 11, 2019 at 3:30:23 PM UTC-4, jbeattie wrote:
On Monday, March 11, 2019 at 10:36:06 AM UTC-7, Mark J. wrote:
On 3/10/2019 8:46 PM, Frank Krygowski wrote:
On 3/10/2019 10:10 PM, John B. Slocomb wrote:
On Sun, 10 Mar 2019 20:21:40 -0400, Frank Krygowski
wrote:

On 3/10/2019 5:52 PM, wrote:
On Sunday, March 10, 2019 at 8:34:24 AM UTC-5,
wrote:
I keep reading see all the bikes coming out and basically all disc
brakes. I cannot believe rim brakes are going to be gone but maybe
I am just kidding myself. I frankly hate the disc brake look and
certainly for a long time parts will be around but are these rim
brakes a dead deal.

Deacon Mark

One of my issues is that I realize we will have rim brake bikes for
awhile but I just hope to keep the nice looks and basic set up. If
it is not broke don't fix the puppy. The one item I have never
experience is the idea on a long descend you can blow a tube. In the
flatlands that to me seems impossible. To blow a tube on a long
descend does the speed have to be really fast like about 40mph or
say at 25mph for a long time. The biggest descend I have done is
about 7% grade total for about a mile and the last say 1/4 mile is
got to 9%. I could easily feather the brakes to avoid heat but maybe
my experience is really limited for true mountain riding. Can you
just pull the brakes up pretty good to get to a speed that is
comfortable. In my case this descend got me to about 43mph my top
speed for sure. Had the it been longer I don't know long I could
have continued before I got to damn scared.

Long, long ago I read a technical article in some bike magazine. (There
used to be real technical articles in bike magazines.) This one was
about brake energy (or really, power in the engineering sense of work
per unit time) and temperature rise during long descents.

The article explained that the braking power depended on brake force and
speed. For any given hill, you could always use the brakes to go super
slow. Brake force will be high, but speed will be low and power will be
low, leading to less temperature rise.

Alternately, you could descend very fast, braking only lightly or not at
all. Brake force will be low or zero. (There's also more aerodynamic
cooling.) This too will lead to less temperature rise.

The author claimed, using lots of calculations summarized in graphs,
that the greatest temperature rise occurred by using the brakes to keep
the speed about 30 mph or 50 kph.

Trouble is, this is exactly the speed lots of cyclists choose for long
descents. Any slower and they feel like slugs. Any faster and they get
scared.

I blew only one tire on a downhill, on the rear of our tandem, creeping
down a short ( 1/10 mile) steep grade well over 10%. We just rode the
bike to the bottom* and I changed the tube. But I can see it would be a
problem if the front tire blew.

Phuket, Thailand has several extremely steep hills on the western side
of the island, steep enough that it is difficult to push a bike up
them.

Out of curiosity I did push the bike up one and coasted down the
eastern side.

Having read all the hoopalla about the rims getting hot and tires
blowing I stopped about half way down and felt the rims... they were,
perhaps, a bit warmer than ambient temperature.

But. As the east side of the hill is a series of "S" turns one can't
just coast down the mountain but must slow down every hundred yards or
so to make the next corner so my braking was a series of pretty hard
brake applications followed by, perhaps, an equal period of coasting..

I have since used that method when descending hills and an occasional
check shows that the rims do not get excessively hot.

Omega and others make temperature indicator dots. They turn black and
stay black when their rated temperature is reached.
https://www.omega.com/pptst/TL-C5_LABELS.html
They're single use products.

Back when Jobst was with us, there was talk of sticking these on some
rims and doing tests, but I don't recall if anyone actually did that, or
what the results were.


Yes, there were tests, I was a test subject. It was in about 1984. I
can't remember for certain, but my guess is the test was sponsored by
Buycycling magazine. I got sent the stick-on temperature indicators.
They were rectangular and had multiple, labeled temp. "windows". When
you reached the indicated temp, the window went (permanently) dark. At
some point I'm sure you sent in results, but I really can't recall that
part.

I'll look in my shop to see if any of the rims (and stickers) are still
around, but I doubt it. In those days we were running 36 spoke rims and
25mm (mis-labeled 1-1/8) Specialized Turbos, and rear rims lasted mostly
a year or two, mostly dying of spoke-hole cracks, and sometimes of
pothole-induced flat spots. Oh to be young and greyhound thin again!



I don't think the selling point for discs is that they prevent your tires from exploding. There has never been a tire-exploding epidemic from over-heating. Like Frank, I blew one tire on a tandem front descending Rocky Point on a hot day. The wet version: https://www.youtube.com/watch?v=-NPqQptjbF0 My wife was on the back yelling at me to slow down, so I complied. This was on a tandem with cantis and no drum or disk brake -- and the rims did get very hot. Discs get super hot on tandems and thus the mega giant 203mm rotors. Tandems are a special case.

Brake fade is a problem with all brakes -- and discs probably get less fade than rim brakes, so heating matters, but the likelihood of blowing a tire off the rim due to over-heating on a road single is pretty remote and not why one would or should buy discs. That's not even something I hear from zealous sales people. The usual pitch is better modulation and stopping in wet weather.

Rim heating was an issue in the tubular days because it didn't take tire-popping heat to soften tubular cement. Having squirming tubulars on a long descent was not uncommon, particularly in hot climates. It was one of the selling points of the new crop of light clinchers in the mid to late '70s. I think discs would be an easy sale to the mountain-climbing clydesdales using CF rims and tubulars.


I've never blown a tire from heat, but I did get hit on the back of the thigh with a small dot of hot glue going down flagstaff road in boulder once.
  #40  
Old March 11th 19, 09:28 PM posted to rec.bicycles.tech
Sir Ridesalot
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Posts: 4,624
Default The death of rim brakes?

On Monday, March 11, 2019 at 3:40:09 PM UTC-4, Frank Krygowski wrote:
On 3/11/2019 3:30 PM, jbeattie wrote:
I think discs would be an easy sale to the mountain-climbing clydesdales using CF rims and tubulars.


That's true and very reasonable.

But you're never going to save the bicycling industry with that kind of
reasonable talk!

--
- Frank Krygowski


Remember back in the days when MTB and touring bicycles cantilevers stuck straight out from the mounting post? IIRC it was Minoura that made a rear rack with a metal hoop that fitted over the cantilever so that saddle bags wouldn't hold the cantilever against the rim. At that time a b icycle with disc brakes would have been very attractive id buyng a new bike.

I also remember reading about disc brakes that one has to be very creful when removing a wheel shortly after using the brakes as the parts can fuse together if the brake lever is accidentally squeezed.
I do see a number of MTB in Canadian Tire stores coming with disc brakes now. I wonder what quality those brake parts are?

If interested here's a link to CT NTB bikes.

https://www.canadiantire.ca/en/sport...ain-bikes.html

Cheers
 




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