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.


--
- Frank Krygowski