Hard braking down hill blowouts

On Mar 28, 11:59*am, Hank wrote:
On Mar 28, 9:30 am, Jay Beattie wrote:





On Mar 28, 8:26 am, Marz wrote:

On Mar 28, 3:49 am, Ben C wrote:

On 2008-03-28, Ben Kaufman wrote:

Is it normal to have blow-outs on a road bike from prolonged hard
braking going about one mile down *a *steep hill *or should superior
wheels and tires be able to deal with the generated heat? *I have an
old panasonic but keep the tires and tubes up to date (PerfomanceBike
GT2 Kevlar, rated at 105 lbs, 26TPI, *which are not the best in the
world but *a heck of a lot better than what my LBS sold me. It is a
27 inch rim and I could not find any better quality tires). *But is it
the tire/wheel quality at issue? *I have been thinking about getting a
new bike rather than trying to *upgrade this one for a number of
reasons (I don't think it's even possible to switch to the current
wheel size) but *the blow-outs are my biggest justification of
expenditure to my wife.

Some math I did earlier:

http://groups.google.co.uk/group/uk....1d32532f671264

It's probably all wrong off course, but my tentative conclusion from it
is that the rims act as heat sinks-- they can soak up quite a lot of
energy, enough for most purposes, but they can't really cope with
sustained braking.

Disks on the other hand have much less heat capacity (because they're
smaller) and probably work hotter, so I reckon they might get up to
temperature quite quickly and then dissipate more because of the bigger
temperature difference with the surrounding air. This would mean they
should be better for continuous braking. In any case they won't make the
tyres pop off.

Disk brakes have their own problems with heat and can 'fade' (fail) on
long downhill sections.

From hayes...

"Brake Fluid Fade - This type of fade occurs when the brake fluid
inside a hydraulic caliper boils. *An important characteristic of
brake fluid is that it is incompressible. *When a brake fluid boils,
gas is formed within the system that is compressible and any lever
stroke available goes toward compressing the gas instead of generating
brake power. *Interestingly enough, when a fluid is under pressure, it
is very difficult for the fluid to boil. *If a brake system is under
pressure, the fluid temperature can rise above the boiling temperature
without the fluid actually boiling. *Once the pressure is released,
the fluid will instantly boil and fade will occur."

A common practice for long downhill sections when using disk brakes is
to brake hard and release as opposed to constant braking to control
speed. The idea being, that when you release you allow the disk to
cool slighty.

I've experienced disk brake fade more often than rim brake blow outs
and that the disk brake fade occurs quicker during a descent than a
rim brake blow out. But, the offroad trails I ride are on average alot
steeper than the roads I ride and also require alot more braking.

I think that is an important point -- road versus trail. *I have done
long road descents on my mechanical disk equiped cross bike without
any brake fade.

Well, yeah - if it's mechanical, the fluid definitely won't boil!- Hide quoted text -

My cables boil! I was thinking of friction material fade. I totally
glossed over the brake fluid boiling issue. It would seem to me that
you could divert brake fluid heat in to a radiant loop to power a
steam generator for the ride up the other side of the hill. Carl can
probably find a filed patent for that. -- Jay Beattie.

Ben Kaufman wrote:
Is it normal to have blow-outs on a road bike from prolonged hard braking going
about one mile down a steep hill or should superior wheels and tires be able
to deal with the generated heat?

It's normal. Pump your brakes rather than having them on all the time,
and stop occasionally to let them cool. That said, it does vary with rim
and tires. It's not the air in the tube expanding because of the heat
that causes the blow out, it's the rim getting too hot.

Are your rims straight side or hook edge? What kind of bead does the GT2
tire have (steel or kevlar)? Sheldon's shop sells some 27" steel bead
tires. See "http://www.sheldonbrown.com/harris/tires/630.html"

Also, for a good and amusing tutorial by Sheldon about folding steel
bead tires, see "http://www.sheldonbrown.com/video/tire-folding.html".
Remember, red is the only color that works, LOL.

On tandems, there was (or is) often a drum brake to use as a drag break
when descending steep hills. A disc brake doesn't work well as a drag
brake, as the rotor will warp and the pad will quickly be worn down.

I have an old panasonic but keep the tires and
tubes up to date (PerfomanceBike GT2 Kevlar, rated at 105 lbs, 26TPI, which are
not the best in the world but a heck of a lot better than what my LBS sold me.
It is a 27 inch rim and I could not find any better quality tires). But is it
the tire/wheel quality at issue? I have been thinking about getting a new bike
rather than trying to upgrade this one for a number of reasons (I don't think
it's even possible to switch to the current wheel size) but the blow-outs are
my biggest justification of expenditure to my wife.

It's a good justification. Get a road bike with disc brakes. It will
eliminate the blow outs, but if you ride with the brakes constantly on
you'll go through a lot of pads and rotors.

Jay Beattie wrote:
On Mar 28, 8:26 am, Marz wrote:

I've experienced disk brake fade more often than rim brake blow outs
and that the disk brake fade occurs quicker during a descent than a
rim brake blow out. But, the offroad trails I ride are on average alot
steeper than the roads I ride and also require alot more braking.

I think that is an important point -- road versus trail. I have done
long road descents on my mechanical disk equiped cross bike without
any brake fade. In fact, in the rain, the disks are far better than
my rim brakes. There is a local 14 mile descent that I did in the
rain/snow on my cross bike with good stopping all the way to the
bottom -- which was a good thing because my hands were frozen, and I
couldn't generate much force on my levers. -- Jay Beattie.

Yeah, the problem with disk brake fade is more common with hydraulic
disk brakes than mechanical disk brakes. Always use non-hydraulic disk
brakes if retro-fitting, and look for mechanical disk brakes on new
bicycles as well.

Jay Beattie wrote:

My cables boil! I was thinking of friction material fade. I totally
glossed over the brake fluid boiling issue. It would seem to me that
you could divert brake fluid heat in to a radiant loop to power a
steam generator for the ride up the other side of the hill.

I use the steam to power a generator that operates by lights.

On Fri, 28 Mar 2008 12:15:25 -0700 (PDT), Jay Beattie
wrote:

My cables boil! I was thinking of friction material fade. I totally
glossed over the brake fluid boiling issue. It would seem to me that
you could divert brake fluid heat in to a radiant loop to power a
steam generator for the ride up the other side of the hill. Carl can
probably find a filed patent for that. -- Jay Beattie.

Dear Jay,

Alas, re-generative braking systems are notoriously inefficient, so
early inventors concentrated on worthier steam-powered bicycles:

http://www.dself.dsl.pipex.com/MUSEU.../steambike.htm

The Michaux steam velocipede is the epitome of elegance and good
looks, but the Roper was far more efficient.

Details on the Roper, whose inventor died while riding it:
http://motorcyclemuseum.org/classics/bike.asp?id=3

Movie with exciting sound track of a Roper replica chugging along:
http://www.lindsaybks.com/gallery/Jo...e/Jorgbike.mov

Cheers,

Carl Fogel

In article
,
Marz wrote:

A common practice for long downhill sections when using disk brakes is
to brake hard and release as opposed to constant braking to control
speed. The idea being, that when you release you allow the disk to
cool slighty.

Yes. The idea is to heat the disc quickly and very
hot. The convective cooling to the air is faster at
higher temperature. The heat transfer to the hub and
brake assemblies is reduced because the disc can cool
to a lower temperature before it is heated again, and
the brake assembly can also cool.

--
Michael Press

Marz wrote:
On Mar 28, 9:03�am, jim beam wrote:
wrote:
Ben C? wrote:
Disks on the other hand have much less heat capacity
Nor do they exchange heat with the tyre.
Indeed. �I wonder if they ever melt the grease in the hub though.
Most bicycle disks are mounted on support spiders so flimsy that heat
conduction to the bearings is insignificant.
"flimsy"??? �is that stanford parlance for "stainless [disk] steel is a
poor conductor"? �or is it presumptive nonsense from someone that
doesn't know what they're talking about?

Disks are very flimsy and are not constructed to resist side to side
forces. They're only 'stiff' in the direction of the rotating wheel.
And not all disks are contructed with stainless steel spiders (see
Hope).

stiffness has absolutely nothing to do with thermal conductivity. or
surface thermal transfer to air.



For example you could poor water on a hot rim to cool it, but the same
action on a disk may (and has for me) warp the bloody thing.

laters,

Marz

Ben C wrote:
On 2008-03-28, Marz wrote:
On Mar 28, 3:49 am, Ben C wrote:
On 2008-03-28, Ben Kaufman wrote:
[...]
Disk brakes have their own problems with heat and can 'fade' (fail) on
long downhill sections.

From hayes...

"Brake Fluid Fade - This type of fade occurs when the brake fluid
inside a hydraulic caliper boils. An important characteristic of
brake fluid is that it is incompressible. When a brake fluid boils,
gas is formed within the system that is compressible and any lever
stroke available goes toward compressing the gas instead of generating
brake power. Interestingly enough, when a fluid is under pressure, it
is very difficult for the fluid to boil. If a brake system is under
pressure, the fluid temperature can rise above the boiling temperature
without the fluid actually boiling. Once the pressure is released,
the fluid will instantly boil and fade will occur."

A common practice for long downhill sections when using disk brakes is
to brake hard and release as opposed to constant braking to control
speed. The idea being, that when you release you allow the disk to
cool slighty.

I've experienced disk brake fade more often than rim brake blow outs
and that the disk brake fade occurs quicker during a descent than a
rim brake blow out. But, the offroad trails I ride are on average alot
steeper than the roads I ride and also require alot more braking.

I have heard of fluid fade affecting bicycle brakes before. It is
shocking in my opinion because that's the easiest kind of fade to fix--
you just need brake fluid that doesn't boil, which exists. There's no
tradeoff or anything, it's a win-win no-brainer. Cars haven't suffered
from fluid fade for years with modern decent brake fluid.

I mentioned this before and someone said it's because bicycle brakes use
crappy brake fluid because it doesn't strip the paint. My advice: use
proper car brake fluid in your bike brakes but pour it in carefully and
don't spill it.

or if you do, wash it off immediately with water. wash, never wipe.

On Fri, 28 Mar 2008 12:29:10 -0400, wrote:

On Thu, 27 Mar 2008 22:06:48 -0400, Ben Kaufman
wrote:

Is it normal to have blow-outs on a road bike from prolonged hard braking going
about one mile down a steep hill or should superior wheels and tires be able
to deal with the generated heat? I have an old panasonic but keep the tires and
tubes up to date (PerfomanceBike GT2 Kevlar, rated at 105 lbs, 26TPI, which are
not the best in the world but a heck of a lot better than what my LBS sold me.
It is a 27 inch rim and I could not find any better quality tires). But is it
the tire/wheel quality at issue? I have been thinking about getting a new bike
rather than trying to upgrade this one for a number of reasons (I don't think
it's even possible to switch to the current wheel size) but the blow-outs are
my biggest justification of expenditure to my wife.

Actual blow outs or is the tire moving on the rim and tearing the stem?

Just asking because the latter is more common but the former more often blamed.

No, the tire stayed on the rim. I heard the bang but at first could not tell
which tire had blown - fortunately, I was going under 10mph at the time. The
location of the failure on the tube was about 1/3 of the way around from the
stem and was a 2 inch appearing "slit." In other blowouts I have felt a tell
tale "thump thump" before it blew, and usually in those the tire is taken off
the rim, which makes the tube replacement process that much faster :-)

Ben

On Fri, 28 Mar 2008 12:47:50 -0700, SMS wrote:

Ben Kaufman wrote:
Is it normal to have blow-outs on a road bike from prolonged hard braking going
about one mile down a steep hill or should superior wheels and tires be able
to deal with the generated heat?

It's normal. Pump your brakes rather than having them on all the time,
and stop occasionally to let them cool. That said, it does vary with rim
and tires. It's not the air in the tube expanding because of the heat
that causes the blow out, it's the rim getting too hot.

Are your rims straight side or hook edge? What kind of bead does the GT2
tire have (steel or kevlar)? Sheldon's shop sells some 27" steel bead
tires. See "http://www.sheldonbrown.com/harris/tires/630.html"

Wow, I see they do still have some name brand 27" tires. Thanks.

My rims are straight. The tire has a wire bead, I just checked the specs.
When I get them from performance they were "folded" but they spring back when
unleashed. The tires that my LBS put on were terrible. I think they were Kenda
brand and they would unseat and blow without provocation.


Also, for a good and amusing tutorial by Sheldon about folding steel
bead tires, see "http://www.sheldonbrown.com/video/tire-folding.html".
Remember, red is the only color that works, LOL.

On tandems, there was (or is) often a drum brake to use as a drag break
when descending steep hills. A disc brake doesn't work well as a drag
brake, as the rotor will warp and the pad will quickly be worn down.

I have an old panasonic but keep the tires and
tubes up to date (PerfomanceBike GT2 Kevlar, rated at 105 lbs, 26TPI, which are
not the best in the world but a heck of a lot better than what my LBS sold me.
It is a 27 inch rim and I could not find any better quality tires). But is it
the tire/wheel quality at issue? I have been thinking about getting a new bike
rather than trying to upgrade this one for a number of reasons (I don't think
it's even possible to switch to the current wheel size) but the blow-outs are
my biggest justification of expenditure to my wife.

It's a good justification. Get a road bike with disc brakes. It will
eliminate the blow outs, but if you ride with the brakes constantly on
you'll go through a lot of pads and rotors.

I didn't know they made road bikes with disk brakes, I was thinking of something
like a Giant OCR C3..hmm I will have to look around some more. It is only this
one steep hill that gives me problems because of the hazards that I must keep
speed down, and of course I tend to keep it braking even harder for fear of
going too fast if I do have a blow out. My assumption, based upon the square of
velocity for kinetic energy is that it would generate less heat if I kept the
speed down to 10mph rather than 20mph (i would be going close to 50 mph without
braking).

Ben