Blowing tube descending

In the flatlands we never worry about this stuff but still seems unreal you could blow a tire by overheating the rims.

How long does the descent need to be and braking? I have taken a mile 5-9% grade down and had to brake in places but does it mean you simply ride the brake continuously to get too much heat.

Have any here had this happen due to heat not poor install or other tire blows.

Deacon Mark

On Mon, 3 Apr 2017 17:49:50 -0700 (PDT),
wrote:
In the flatlands we never worry about this stuff but still seems
unreal you could blow a tire by overheating the rims.

How long does the descent need to be and braking? I have taken a mile
5-9% grade down and had to brake in places but does it mean you simply
ride the brake continuously to get too much heat.

Have any here had this happen due to heat not poor install or other
tire blows.

If you ride tubulars, the heat can soften the glue holding them on and
the tire can roll off the rim (not unlike using heat to soften the glue
on a guitar)

If you ride clinchers, the heat softens the rubber on the bead and it
can become slippery and slide over the edge of the rim. That allows the
tube to escape and BANG.

These events tend to happen on prolonged descents with a lot of braking
for a fairly long time (or really steep descents for a shorter time).
All of the heat caused by the friction of the pads against the rim goes
into the rim because the pads are insulators. Some riders have reported
getting pelted in the back of the legs by hot bits of brake pad, but
I've never had that happen.

Even our own Jobst had it happen in the Alps, resulting in a crash and a
broken leg, despite his advocacy to "let it roll" on the descents for
this reason.

On Monday, April 3, 2017 at 6:39:48 PM UTC-7, Tim McNamara wrote:
On Mon, 3 Apr 2017 17:49:50 -0700 (PDT),
wrote:
In the flatlands we never worry about this stuff but still seems
unreal you could blow a tire by overheating the rims.

How long does the descent need to be and braking? I have taken a mile
5-9% grade down and had to brake in places but does it mean you simply
ride the brake continuously to get too much heat.

Have any here had this happen due to heat not poor install or other
tire blows.

If you ride tubulars, the heat can soften the glue holding them on and
the tire can roll off the rim (not unlike using heat to soften the glue
on a guitar)

If you ride clinchers, the heat softens the rubber on the bead and it
can become slippery and slide over the edge of the rim. That allows the
tube to escape and BANG.

These events tend to happen on prolonged descents with a lot of braking
for a fairly long time (or really steep descents for a shorter time).
All of the heat caused by the friction of the pads against the rim goes
into the rim because the pads are insulators. Some riders have reported
getting pelted in the back of the legs by hot bits of brake pad, but
I've never had that happen.

Even our own Jobst had it happen in the Alps, resulting in a crash and a
broken leg, despite his advocacy to "let it roll" on the descents for
this reason.

From Mark Hickey himself:
https://groups.google.com/forum/#!searchin/rec.bicycles.tech/jobst$20brandt$20descending$20blow$20clincher$20of f$20rim$20hicks%7Csort:relevance/rec.bicycles.tech/c-7gyqVVeMM/FD8yzVYRIR8J

On 4/3/2017 8:49 PM, wrote:
In the flatlands we never worry about this stuff but still seems unreal you could blow a tire by overheating the rims.

How long does the descent need to be and braking? I have taken a mile 5-9% grade down and had to brake in places but does it mean you simply ride the brake continuously to get too much heat.

Have any here had this happen due to heat not poor install or other tire blows.

After it's happened, I suppose it's not possible to tell if it was due
to a poor install or not.

I've had several blowouts. The first was when our tandem was brand new,
sitting inside the house. I'd put its first set of tires on and heard
the loud explosion about an hour later. I assume that was bad
installation, although it still surprises me. Why would it take so long
to creep loose?

Maybe ten years later the tandem blew a back tire on one very short (1/4
mile?) very steep (15% grade?) hill. We were descending slowly due to
the stop sign at the bottom. Both of those tandem blowouts were with
old Weinmann rims which were not the modern "hook bead" design. Hook
beads are much better, I think.

Once on a 1992 tour in Ireland, we rode a very rough towpath trail for a
few miles, then stopped for a snack in a town square. After about ten
minutes, my daughter's front tire blew as the bike was just sitting
parked. I think that was with a non-hooked-bead rim, too. I wondered
if the rocky trail had somehow knocked her tire askew.

I remember when one fellow club member, sort of a novice rider, blew a
tire just after a steep descent of about a half mile. His bike was
pretty new, about 2010 issue, I think. I'm sure it had modern hook bead
rims. I can't say whether he had botched the tire installation or not.


--
- Frank Krygowski

On Mon, 3 Apr 2017 17:49:50 -0700 (PDT), wrote:

In the flatlands we never worry about this stuff but still seems unreal you could blow a tire by overheating the rims.

How long does the descent need to be and braking? I have taken a mile 5-9% grade down and had to brake in places but does it mean you simply ride the brake continuously to get too much heat.

Have any here had this happen due to heat not poor install or other tire blows.

Deacon Mark

Jobst Brandt wrote rather extensively about wheel/tire overheating and
in one of his dissertations mentions lowering tire pressure to prevent
blow outs. He also mentioned that "can't touch it" hot for more than
1 minute was sort of the danger line. He also mentions that as
descending speed increases that air drag increases and tire/rim
cooling is improved due to greater air flow.
--
Cheers,

John B.

On 4/3/2017 11:35 PM, John B. wrote:
On Mon, 3 Apr 2017 17:49:50 -0700 (PDT), wrote:

In the flatlands we never worry about this stuff but still seems unreal you could blow a tire by overheating the rims.

How long does the descent need to be and braking? I have taken a mile 5-9% grade down and had to brake in places but does it mean you simply ride the brake continuously to get too much heat.

Have any here had this happen due to heat not poor install or other tire blows.

Deacon Mark

Jobst Brandt wrote rather extensively about wheel/tire overheating and
in one of his dissertations mentions lowering tire pressure to prevent
blow outs. He also mentioned that "can't touch it" hot for more than
1 minute was sort of the danger line. He also mentions that as
descending speed increases that air drag increases and tire/rim
cooling is improved due to greater air flow.

I once saw a technical article that evaluated energy (or actually,
power) input to the rim vs. speed, for a range of hill steepness. Power
can be computed as force times velocity; and that power is directly
related to the heat the rim has to dissipate.

See, if you descend a hill slowly, there's a lot of braking force but
not much velociy, so braking power is low. Rim temperatures stay low.

If you descend that same hill at a high speed, you're not applying as
much brake force, since aerodynamic drag is doing a lot more. Rim
temperatures again stay low. But it takes guts to let it roll and not
hit the brakes.

According to the article, most riders run out of guts at speeds higher
than about 30 mph. And 30 mph happens to be the speed at which braking
power is highest for most riders and most hills. In other words, most
riders descend at the speed that generates the most rim heating.


--
- Frank Krygowski

On 04-04-17 02:49, wrote:
In the flatlands we never worry about this stuff but still seems unreal you could blow a tire by overheating the rims.

How long does the descent need to be and braking? I have taken a mile 5-9% grade down and had to brake in places but does it mean you simply ride the brake continuously to get too much heat.

Have any here had this happen due to heat not poor install or other tire blows.

Deacon Mark


Years ago I had such a blowout on a descent with lots of switchbacks. I
let the bike coast on the straight stretches and braked hard for the
switchbacks. The result is shown he https://flic.kr/p/9XmmWn .
Fortunately I could still stop safely.

I now try for intermittent braking all the way down, so generally going
slower and hoping that short stretches of coasting will let the rims
cool a bit. I'm not sure whether this is really better, but at least I
haven't had any more such flats. And my new mountain bike has disc brakes.

Ned

On Mon, 3 Apr 2017 23:51:18 -0400, Frank Krygowski
wrote:

On 4/3/2017 11:35 PM, John B. wrote:
On Mon, 3 Apr 2017 17:49:50 -0700 (PDT), wrote:

In the flatlands we never worry about this stuff but still seems unreal you could blow a tire by overheating the rims.

How long does the descent need to be and braking? I have taken a mile 5-9% grade down and had to brake in places but does it mean you simply ride the brake continuously to get too much heat.

Have any here had this happen due to heat not poor install or other tire blows.

Deacon Mark

Jobst Brandt wrote rather extensively about wheel/tire overheating and
in one of his dissertations mentions lowering tire pressure to prevent
blow outs. He also mentioned that "can't touch it" hot for more than
1 minute was sort of the danger line. He also mentions that as
descending speed increases that air drag increases and tire/rim
cooling is improved due to greater air flow.

I once saw a technical article that evaluated energy (or actually,
power) input to the rim vs. speed, for a range of hill steepness. Power
can be computed as force times velocity; and that power is directly
related to the heat the rim has to dissipate.

See, if you descend a hill slowly, there's a lot of braking force but
not much velociy, so braking power is low. Rim temperatures stay low.

If you descend that same hill at a high speed, you're not applying as
much brake force, since aerodynamic drag is doing a lot more. Rim
temperatures again stay low. But it takes guts to let it roll and not
hit the brakes.

According to the article, most riders run out of guts at speeds higher
than about 30 mph. And 30 mph happens to be the speed at which braking
power is highest for most riders and most hills. In other words, most
riders descend at the speed that generates the most rim heating.

I had never though of that way but it is certainly true. But too, I've
never had any problems with rim over heating, probably because I don't
ride in hills much :-)

When we lived in Jakarta I had a lovely "Sunday" route from S. Jakarta
to Bogor and back. a 50 km climb, as I remember one or two gears lower
than level ground. The return was 50 Km of downhill. Wheeee :-)
--
Cheers,

John B.

On Monday, April 3, 2017 at 8:51:21 PM UTC-7, Frank Krygowski wrote:
On 4/3/2017 11:35 PM, John B. wrote:
On Mon, 3 Apr 2017 17:49:50 -0700 (PDT), wrote:

In the flatlands we never worry about this stuff but still seems unreal you could blow a tire by overheating the rims.

How long does the descent need to be and braking? I have taken a mile 5-9% grade down and had to brake in places but does it mean you simply ride the brake continuously to get too much heat.

Have any here had this happen due to heat not poor install or other tire blows.

Deacon Mark

Jobst Brandt wrote rather extensively about wheel/tire overheating and
in one of his dissertations mentions lowering tire pressure to prevent
blow outs. He also mentioned that "can't touch it" hot for more than
1 minute was sort of the danger line. He also mentions that as
descending speed increases that air drag increases and tire/rim
cooling is improved due to greater air flow.

I once saw a technical article that evaluated energy (or actually,
power) input to the rim vs. speed, for a range of hill steepness. Power
can be computed as force times velocity; and that power is directly
related to the heat the rim has to dissipate.

See, if you descend a hill slowly, there's a lot of braking force but
not much velociy, so braking power is low. Rim temperatures stay low.

If you descend that same hill at a high speed, you're not applying as
much brake force, since aerodynamic drag is doing a lot more. Rim
temperatures again stay low. But it takes guts to let it roll and not
hit the brakes.

According to the article, most riders run out of guts at speeds higher
than about 30 mph. And 30 mph happens to be the speed at which braking
power is highest for most riders and most hills. In other words, most
riders descend at the speed that generates the most rim heating.

I've never had a blow-out (kaboom event), although I did have a flat on a tandem. Leonard Zinn chalks-up kaboom events to bad tube installation. http://www.velonews.com/2010/01/bike...low-out_103005

Who knows. The only real problem I had was riding sew-ups on long descents in California heat. I've done tons of descending on a single bike with clinchers and never had a problem.

And a lot of descending is not even about guts (well, not a lack of reasonable guts). There are steep, twisting descents where you can't reasonably let the bike run. These descents are common in lots of places, and yet there is a pretty low incidence of tires blowing off, AFAIK. This bolsters Zinn's bad-installation theory.

-- Jay Beattie.

On Monday, April 3, 2017 at 8:49:53 PM UTC-4, wrote:
In the flatlands we never worry about this stuff but still seems unreal you could blow a tire by overheating the rims.

How long does the descent need to be and braking? I have taken a mile 5-9% grade down and had to brake in places but does it mean you simply ride the brake continuously to get too much heat.

Have any here had this happen due to heat not poor install or other tire blows.

My rear tire blew on a descent into Conway, Wales, in 1972. I could not identify a cause, it may have been overheating, but this seems unlikely on Raleigh Lenton Sports 10-speed with 26x1&3/8ths tires on Sturmey-Archer steel rims and Sturmey-Archer caliper brakes. The tube blew out of the tire and literally broke the bead, which came free of the carcass. The tubes wrapped around the freewheel and I landed in a bed of nettles. I had to borrow me mate's bike, cycle into Conway, find an open shop, by a "tyre" and tube, and cycle back up the hill. Blew the hell out of the afternoon.
--
Andrew Chaplin
SIT MIHI GLADIUS SICUT SANCTO MARTINO