On 3/11/2019 12:30 PM, 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:
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.

Yup. My one front-tire blowout was on a tandem loaded with baggage, but
it was caused by young-and-stupid, not by heat. I had let the front
tire go too far and worn a hole through the casing /on top of the
tread!/ I still can't figure out how I missed the warning signs - a
front tire worn that bad should be obvious, even on a tandem. To
compound the matter, we were going down a steep hill, but fortunately on
a wide straight road. I was able to keep it upright until we came to a
stop, and I had a spare (so maybe I /had/ noticed the warning signs!)

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.

Also for some clinchers back in the day when many clincher rims didn't
have a bead "hook" - I heard a report of first-hand experience with a
blowout on a descent on a bike with, um, large riders on it, around
1975. I don't know the rim, but he was using Schwinn LeTour tires,
which were pretty nice (Japanese made, maybe by Panasonic?) except that
they fit loosely as I recall. That's just before the revolution in
widely available high-quality clinchers. He told me the tire came clean
off the rim. Dunno what injuries, if any.

-Mark J.