Blowing tube descending

[deaco...@gmail.com]

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

[Tim McNamara]

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.

[Doug Landau]

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

[Frank Krygowski]

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

[John B.]

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.

[Frank Krygowski]

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

[Ned Mantei]

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 here: 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

[John B.]

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.

[jbeattie]

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/bikes-and-tech/technical-faq/technical-faq-avoiding-that-frightening-blow-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.

[ab.ch...@rogers.com]

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

[cycl...@gmail.com]

We have a lot of hills in the San Francisco bay area and I can't remember ever getting a flat from riding the brakes including one mile long 18% grade so I think that your blowout was a fluke from either a pinch during installation which made a weak spot in the tube or a manufacturing error. I have found these in the cheap tubes from Performance Bicycle. You can inflate the tire and a half hour later you can have it explode. Or you can come out the next day for a ride and the tire will be flat.

Continental tubes don't do this but they are expensive.

[cycl...@gmail.com]

At Bikekit Pro the Continental tubes for a 23 mm tire are $9 apiece. Though at that price maybe they just give you the drive to be extra careful when mounting.

[Andrew Chaplin]

cycl...@gmail.com wrote in
news:50c19bb3-a7a9-40a3...@googlegroups.com:

They're CAD 7.99 plus tax here, which seems odd, since Canadians generally
get hosed when it comes to bicycle part prices.

--
Andrew Chaplin
SIT MIHI GLADIUS SICUT SANCTO MARTINO

(If you're going to e-mail me, you'll have to get "yourfinger." out.)

[Roger Merriman]

myself no, I grew up in area with both short and very steep and longer
shallower climbs though I'm more MTB than roadie.

longest decent i've done is just shy of 22 miles I've done it few times
now, not thus far had problems with the rim warming much.

I'm sure some can get into trouble one only has to go on
charity/sportives etc to see that riding ablity covers quite a range!

Roger Merriman

[retrog...@gmail.com]

I beg to disagree. On one of my favorite rides near Placerville, CA, going southeast on Buck's Bar Road, you descend 670 feet to the Cosumnes River in less than a mile. On a hot day, that will heat up my Mavic Open Sport rims so the heat is conducted up the metal valve stem and the tube fails at its base. It always happens just as you start the ascent from the Cosumnes gorge to the town of Somerset, so it is rather discouraging. Therefore I've made it a habit of stopping halfway down the descent at a Cosumnes River overlook to let my rims cool.

[Duane]

On 19/04/2017 9:43 PM, retrog...@gmail.com wrote:
> I beg to disagree. On one of my favorite rides near Placerville, CA, going southeast on Buck's Bar Road, you descend 670 feet to the Cosumnes River in less than a mile. On a hot day, that will heat up my Mavic Open Sport rims so the heat is conducted up the metal valve stem and the tube fails at its base. It always happens just as you start the ascent from the Cosumnes gorge to the town of Somerset, so it is rather discouraging. Therefore I've made it a habit of stopping halfway down the descent at a Cosumnes River overlook to let my rims cool.
>

Disagree with what? Maybe copy a bit of what you're replying to...

I think you mean about blowing tubes with hot rims. I've done some
rides in New Hampshire with long descents and though I haven't lost a
tube, a friend did. In my case I could smell the rubber burning on the
pads but was able to let off on straights long enough to cool the rims
though it was a bit hairy. I expect out west the descents are probably
longer.

[retrog...@gmail.com]

Duane wrote: Disagree with what? Maybe copy a bit of what you're replying to...

Sorry, Duane, but I thought there was a clear consensus in the foregoing posts that blowouts from rim heat due to descending don't really happen anymore.

[cycl...@gmail.com]

On Thursday, April 20, 2017 at 6:16:10 AM UTC-7, retrog...@gmail.com wrote:
> Duane wrote: Disagree with what? Maybe copy a bit of what you're replying to...
>
> Sorry, Duane, but I thought there was a clear consensus in the foregoing posts that blowouts from rim heat due to descending don't really happen anymore.

Can you suggest why blowing out a tube would be worse than pushing a worn-out disk pad out the side of the actuator and ending up with no brakes at all?

Disks seem to be the great fix but after my using them they have a lot of weaknesses. They are generally too strong and far too easy to lock a wheel, especially off-road. The pads are far too shallow and wear out very rapidly. Talking about ceramic pads is a bit funny to me since instead of wearing the pad you then wear the disk. In any case you can rapidly lose the full length that the actuator will move.

A disk brake is all about leverage. So the total movement of the pad is very slight so that the implied lever arm can be long. So it doesn't take much wear anywhere in the system to lose total brakes.

There are limits to everything. If you are blowing tubes because of overheating rims you are going too fast. Or you are braking too much.

I can't say I'm an expert off-road but I can get along. I've had my share of crashes and as a rule they have been so damn scary that I've always had time to situate my body so that I don't land on my head. That's a hell of a lot more than I can say about road bikes where you are generally going so fast and so close to the ground that there's no time to think and head injuries are fairly common. So as I get older I am taking more and more of an upright posture not because I have trouble getting down on the drops but because it gives me more options in a crash.

I've actually seen MTB riders step off of a bike in a crash without actually falling off at pretty high speeds. Don't try this at home.

[jbeattie]

On Thursday, April 20, 2017 at 6:40:01 AM UTC-7, cycl...@gmail.com wrote:
> On Thursday, April 20, 2017 at 6:16:10 AM UTC-7, retrog...@gmail.com wrote:
> > Duane wrote: Disagree with what? Maybe copy a bit of what you're replying to...
> >
> > Sorry, Duane, but I thought there was a clear consensus in the foregoing posts that blowouts from rim heat due to descending don't really happen anymore.
>
> Can you suggest why blowing out a tube would be worse than pushing a worn-out disk pad out the side of the actuator and ending up with no brakes at all?
>
> Disks seem to be the great fix but after my using them they have a lot of weaknesses. They are generally too strong and far too easy to lock a wheel, especially off-road. The pads are far too shallow and wear out very rapidly. Talking about ceramic pads is a bit funny to me since instead of wearing the pad you then wear the disk. In any case you can rapidly lose the full length that the actuator will move.
>
> A disk brake is all about leverage. So the total movement of the pad is very slight so that the implied lever arm can be long. So it doesn't take much wear anywhere in the system to lose total brakes.
>
> There are limits to everything. If you are blowing tubes because of overheating rims you are going too fast. Or you are braking too much.

I guess I haven't had any problems with discs that would disqualify them from use. I have had problems with rims over-heating -- although only on a tandem or with sew-ups. I was flying down Page Mill on a hot summer day 40 years ago with squirming sew-ups, and I was so worried about braking that when a squirrel ran out in front of me, I just ran over it.

Anyway, if you're on a long, steep, twisting descent, probably the only thing you can do is stop every so often to let your rims cool and maybe even your discs. Well, you could avoid the descent, but what fun is that.


For Retrogrouch: be happy you're not coming up the other side of that climb. It works out to an average 12%.

-- Jay Beattie

[cycl...@gmail.com]

A couple of years ago when the Tour of California was doing several stages in the area I was flying down Page Mill with a couple of friends and coming up was what looked like the Stanford group with perhaps 50 in the group FLYING up and taking up the entire lane.

I don't remember any of the climbs in that area being particularly troublesome. On one of them I was with a large group and the front half disappeared and a city crew stopped my group. They were cutting a tree down and it took about a half hour. You should have heard the other group when we got to the top. They thought we had forgotten how to climb.

[Duane]

On 20/04/2017 9:16 AM, retrog...@gmail.com wrote:
> Duane wrote: Disagree with what? Maybe copy a bit of what you're replying to...
>
> Sorry, Duane, but I thought there was a clear consensus in the foregoing posts that blowouts from rim heat due to descending don't really happen anymore.
>

No problem. Just that threads around here tend to wander and I don't
keep old posts.

If that was the consensus, then I agree with you that it can still
happen. Although I also know that if you can let the brakes go for a
bit the fast descent cools the rims as well.

I don't have disk brakes on my bike but I can see why some people do.
Jay rides a lot in the rain in a very hilly area for example...

[retrog...@gmail.com]

Duane wrote: "If you are blowing tubes because of overheating rims you are going too fast. Or you are braking too much."

Yes, I probably brake a lot and descend slower than a lot of other riders. Part of that is because I'm an old guy, but you know what? I haven't fallen off the bike in a long time!

Jay wrote "For Retrogrouch: be happy you're not coming up the other side of that climb. It works out to an average 12%."

Yes, I have done that climb a number of times. When I was younger I could do it without stopping, but now I really hate it because I have to get off the dam*ed bike and rest at least once. I don't like to have to do that! People tell me I should get a lower gear, but I dunno. My low is 35 inches, and I think that the day that I am too weak to push that gear will probably be the day I quit riding.

[Duane]

Thanks for the quote but I didn't say:

"If you are blowing tubes because of overheating rims you are going too
fast. Or you are braking too much."

I can't really parse that. The people that I've seen blowing tubes
because of overheating it was generally caused by them wanting to not go
too fast for conditions.

The situation that I described when my rims were overheating, I had a
choice to brake enough to slow in the curves, go off the mountain or
stop and walk. I was able to manage without walking or blowing a tube
but the smell of the rubber burning scared the hell out of me. <g>

[Frank Krygowski]

On 4/20/2017 10:15 AM, jbeattie wrote:
> I have had problems with rims over-heating -- although only on a tandem or with sew-ups. I was flying down Page Mill on a hot summer day 40 years ago with squirming sew-ups, and I was so worried about braking that when a squirrel ran out in front of me, I just ran over it.

PETA agents will be pounding on your door soon.

I'm proud to say that no animals were harmed during my two bike rides
yesterday.

--
- Frank Krygowski

[Frank Krygowski]

Again, according to one technical article from long ago, for a lot of
grades, maximum rim temperature occurs when you try to hold the speed to
about 30 mph. Descending slower inputs energy into the system at a
slower rate. Descending faster allows aerodynamic drag to take some of
the load.

Unfortunately, 30 mph is about the speed a lot of riders choose for fast
downhills.


--
- Frank Krygowski

[John B Slocomb]

What I've always done on hills that were either super steep or had
corners that limited safe speeds was to brake as hard as I could to
near walking speed and then release the brakes until the speed seemed
excessive and then brake again. The theory was to get the bike slowed
down and then allow the rims to cool during the non-braking phase.

I have no idea whether this is effective other then to say that I
never had a tire explode :-)

[Joy Beeson]

On Thu, 20 Apr 2017 08:45:27 -0700 (PDT), retrog...@gmail.com
wrote:

> My low is 35 inches, an=
> d I think that the day that I am too weak to push that gear will probably b=

> e the day I quit riding.

When I had very low gears put on my first real bike, I said to the
mechanic, "I'll be back to get higher gears after when I've built up
some muscle." He answered "No, you will climb steeper hills."

And I'm still riding those gears. But if I make a habit of riding on
150 W, which has a very steep dip with a divided highway in the
valley, I may ask the Trailhouse whether they can install a bigger
inside cog -- I know that I'm already using the smallest-possible
inner chainwheel.

On the other hand, just after I cross US 30, there's a convenient
driveway where I cam pull off and change into walking shoes, and it's
only two miles from there to city streets where I'd want walking shoes
anyway. And all downhill, once I've walked to the top.

Meanwhile, I'm walking down every staircase I can, and if nobody is
looking, I'll walk up backward.

I've learned a new trick for climbing hills when seventy-six: when I
see a hill I'm not sure I can climb, I sit down at the top of the
previous hill and rest for five minutes by the clock. Then I pedal as
fast as I can coming down, and find the climb fairly easy.

--
joy beeson at comcast dot net
http://wlweather.net/PAGESEW/
The above message is a Usenet post.
I don't recall having given anyone permission to use it on a Web site.

[cycl...@gmail.com]

I think that you got those quotes a little mis-ascribed. That was me. And I do not think that going too slow is a problem. Going too fast and then trying to slow up often is. If you ride more slowly there is a lot less energy going into the brakes and hence the rim.

As for climbing - it's just the F-ing weather. Once the sun comes out and we can ride often enough the fitness will come back. I had to stop three times going up Palomares last time. I NEVER stop on Palomares. Even coming up the steep side I am dying over the last 100 feet but I don't have to stop.

And I feel like crap all the time now because I can't ride for one reason or another - mostly weather related but I'm getting cataract surgery now as well. Despite the doctor's advice as soon as there was a clear day I did a nice easy 25 miles.

[cycl...@gmail.com]

I've always done this as well on steep hills with dangerous turns in them.

[cycl...@gmail.com]

When you look at a climb it is almost always far more daunting in prospect than in reality.

[Sir Ridesalot]

On Friday, April 21, 2017 at 10:23:43 AM UTC-4, cycl...@gmail.com wrote:
Snipped

>And I do not think that going too slow is a problem. Going too fast and then trying to slow up often is. If you ride more slowly there is a lot less energy going into the brakes and hence the rim.
>

Snipped

The problem is that in order to go slow on a lot of long descents a fair number of people ride the brakes constantly and that's what heats up the rims enough to cause a tire to blow or in the case of a tubular to roll off the rim.

Going fast, braking hard, going fast and so on allows the rim to cool between applications of the brake.

Cheers

[Duane]

Well that was the part that I didn't get. The advice to ride more
slowly on a long descent in order to not burn up your brakes. What
would be the other technique, aside from braking, to ride more slowly on
a long descent? Parachute? Get off and walk?

You're right about not riding the brakes but when you have curves
involved it's more difficult. I've never blown a tube like that though
so it's not impossible. Just more difficult.

[Frank Krygowski]

On 4/21/2017 11:19 AM, Duane wrote:
>
>
> Well that was the part that I didn't get. The advice to ride more
> slowly on a long descent in order to not burn up your brakes. What
> would be the other technique, aside from braking, to ride more slowly on
> a long descent? Parachute? Get off and walk?

Using the brakes to ride descents more slowly does reduce brake
temperatures. Think of a limiting case: applying brakes hard enough to
descend a hill at 3 mph. The temperature rise won't be great, because
the rate of energy input is low.

More detail: On a given slope, if aero drag is small enough to neglect,
the brake force needed to maintain constant speed is the same whether
the descending speed is 3 mph or 30 mph. That's simple physics.

But the power that must be dissipated by the brake system is that
braking force times the speed; so 30 mph instead of 3 mph puts ten times
as much power (that is, energy per unit time) into the brake system.

In that case, temperatures of rims and brake blocks, or discs and pads,
will rise until heat loss rate equals input power. Higher temperature
differentials are needed to reject heat faster. So equilibrium
temperature is higher for higher constant descending speeds - that is,
until you start getting significant help from aerodynamic drag.


--
- Frank Krygowski

[Ned Mantei]

I think that the timing of rolling down vs. braking may need to be
better defined. For disc brakes a local bike parts company suggests 2
second bursts of braking and 2 seconds of rolling, which might also be
appropriate for rim brakes. Some 10 years ago I was rolling down about
500 meters on a road with 10 switchbacks or at least sharp turns. I was
letting the bike roll on the straighter stretches and then braking hard
for the turns (with rim brakes). To again link to a photo that I already
referred to earlier in this thread, the tube on the front wheel didn't
like this at all: https://flic.kr/p/9XmmWn . Fortunately the tire stayed
on the rim, and I was able to stop safely. Since then I have been much
more cautious.

Ned

[cycl...@gmail.com]

It's all a math problem. If you go slow enough although you're dragging your brakes, too little energy is going into the brakes to burn them or the rims enough to blow a tube.

Faster (20+) on a long descent and you can overheat everything.

Going very fast and braking for the turns also reveals less energy into the rims (high energy short duration). It also increases the cooling air over the rim.

So blowing tubes is from not going slow enough.

[retrog...@gmail.com]

It doesn't seem to me that the discussion is taking into account the fact that the bike's kinetic energy (to be dissipated by the brakes as heat) is proportional to its velocity squared. So it is better to keep your velocity as low as possible, right?

[AMuzi]

On 4/23/2017 3:48 PM, retrog...@gmail.com wrote:
> It doesn't seem to me that the discussion is taking into account the fact that the bike's kinetic energy (to be dissipated by the brakes as heat) is proportional to its velocity squared. So it is better to keep your velocity as low as possible, right?
>

How much fun could that possibly be?


--
Andrew Muzi
<www.yellowjersey.org/>
Open every day since 1 April, 1971

[Frank Krygowski]

On 4/23/2017 4:48 PM, retrog...@gmail.com wrote:
> It doesn't seem to me that the discussion is taking into account the fact that the bike's kinetic energy (to be dissipated by the brakes as heat) is proportional to its velocity squared. So it is better to keep your velocity as low as possible, right?

Keeping your velocity low is one way to prevent blowouts from
overheating brakes & rims. Letting your velocity get very high is
another, assuming the road allows that. At high speeds, the aero drag
does a lot of the braking for you. If you're gutsy enough, you may not
need to use the brakes at all.

--
- Frank Krygowski

[OSHA]

A long time ago one of the technical mags (Cycling Science? Bike
Tech?) had an article where the author did a bunch of calculations to
characterize heat generated while braking and then found the maximum
to be about 1/2 the free decent velocity. (So, if you descend a hill
at 30 kph without any braking, maximum heat will be generated when
holding the bike to 15 kph).

Sadly, I don't recall the actual math.

[John B Slocomb]

Didn't Brandt participate in some brake/temperature tests? I seem to
remember mention of it but I never read any results.

[cycl...@gmail.com]

I believe you will find that it's a bit more complicated than that. I will have to think about this but presently am in an argument about quantum physics.

[Frank Krygowski]

IIRC, he was tinkering away on that project about the time he had his
final crash. I don't think it got far enough to have noteworthy results.


--
- Frank Krygowski