Drum-Brake Reliable for Long, Steep Descents?

[Elisa Francesca]

Quoting myself in another thread:

<<I'm looking around now at some upmarket bikes for when I grow up. I will be needing a comfort or
utility style bike that can be ridden in a skirt, carry lots of shopping, and tackle very steep
hills (i.e. it should have a fairy gear and rock-hard brakes).>>

The bike by Giant that I was looking at over the weekend had a V-brake on the front wheel and a
drum-brake on the back wheel. The salesman told me this was for greater reliability in rainy
weather. However, I checked up what John Forrester had to say about this in EFFECTIVE CYCLING.
Although I find his prose really hard to understand, I dimly intuited that he thinks any kind of
brake on the hub, including a drum brake, will fail over more than 750 yard descents because it
cannot evacuate heat sufficiently. I gather he recommends side-pull rim-brakes for this kind of
application. Also he is strongly against unequal configurations on the front and back wheels.

My descent goes on for almost 1.5 km and is _seriously_ steep. So much so that I have not been able
to trust the V-brakes of my cheap-and-cheerful supermarket bike - I walk the bike over this passage
of the trip, both going uphill (because the lowest gear is no low enough) and downhill because I
cannot trust those flimsy brakes with my considerable poundage (I weigh over 200 lb alas). So this
section alone takes up 35% of my travel time although it is only 15% of my distance.

Does this group have opinions on the subject of brakes on steep descents? Is the reliability of the
brakes an important factor in the overall price of a bike? I mean is the cheapness of my current
bike (140 Euros, as opposed to 800 Euros for the Giant) likely to correlate with flimsy brakes, or
is the price of reliable brakes fairly constant over all price ranges? And should I be avoiding drum
brakes like the plague?

Many thanks,

Elisa francesca Roselli Ile de France

 

[Alex Rodriguez]

check into bikes with disc brakes front and rear. They are pretty common nowadays. Then you won't
have to walk down the hill and you won't have to worry about overheating your brakes/rims.
-----------------
Alex __O _-\<,_ (_)/ (_)

 

[Pete]

"Elisa Francesca Roselli" <[email protected]> wrote in message
news:[email protected]...
> Quoting myself in another thread:
>
> <<I'm looking around now at some upmarket bikes for when I grow up. I will be needing a comfort or
> utility style bike that can be ridden in a skirt, carry lots of shopping, and tackle very steep
> hills (i.e. it should have a fairy gear and rock-hard brakes).>>
>
> The bike by Giant that I was looking at over the weekend had a V-brake on the front wheel and a
> drum-brake on the back wheel. The salesman told me this was for greater reliability in rainy
> weather.

Possibly better water protection, but also possibly marketing speak.

> However, I checked up what John Forrester had to say about this in EFFECTIVE CYCLING. Although I
> find his prose really hard to understand, I dimly intuited that he thinks any kind of brake on the
> hub, including a drum brake, will fail over more than 750 yard descents because it cannot evacuate
> heat sufficiently.

Possibly.

> I gather he recommends side-pull rim-brakes for this kind of application. Also he is strongly
> against unequal configurations on the front and back wheels.

Not necessarily bad. After all, you use the front and back completely different. It's just a matter
of getting used to the differences.

> My descent goes on for almost 1.5 km and is _seriously_ steep. So much so that I have not been
> able to trust the V-brakes of my cheap-and-cheerful supermarket bike - I walk the bike over this
> passage of the trip, both going uphill (because the lowest gear is no low enough) and downhill
> because I cannot trust those flimsy brakes with my considerable poundage (I weigh over 200 lb
> alas). So this section alone takes up 35% of my travel time although it is only 15% of my
> distance.

Please tell us your rims are not chrome plated steel, but instead they are made of an alloy (not a
polished surface).

> Does this group have opinions on the subject of brakes on steep descents? Is the reliability of
> the brakes an important factor in the overall price of a bike?

Yes, most assuredly. Inexpensive brakes (drum, V, canti, disc) quite often are built from not too
great materials. And have a lot of flex. And poor quality pads. Squeeze all you want, and you'll
never achieve full braking.

> I mean is the cheapness of my current bike (140 Euros, as opposed to 800 Euros for the Giant)
> likely to correlate with flimsy brakes,

You don't have to spend 800, but 140 may be a bit low.

> or is the price of reliable brakes fairly constant over all price ranges?

No. Brake levers, arms, and pads all come into play.

> And should I be avoiding drum brakes like the plague?

Not necessarily. Especially drum on the rear, because you do not use the rear as hard as the front.
You DO use the front brake more, don't you?

Pete

 

[ireman_1]

My cruiser has drum brakes on it and they are NOT meant to provide either great or constant braking. They are good brakes for mellow riding or well, cruisers and commuters that are not working on fitness or interval times basically. They work fine in the rain, but not much better than a decent set of v-brakes. The only "cool" thing about them is they provide for clean lines on your rig and are not the norm. You can buy great v-brakes (shimano XT) for not much more than $100 (US) if you shop around on the net. Not that I live in Europe, but from reading some posts around and watching what's available, you should be able to get something with good v-brakes for 800 euro and be every bit capable of the hill you mention. Good luck and keep shopping. It sounds like the shop you went to wasn't working very hard for you and that IS their job. Take care.

K.

Originally posted by Elisa Francesca
Quoting myself in another thread:

<<I'm looking around now at some upmarket bikes for when I grow up. I will be needing a comfort or
utility style bike that can be ridden in a skirt, carry lots of shopping, and tackle very steep
hills (i.e. it should have a fairy gear and rock-hard brakes).>>

The bike by Giant that I was looking at over the weekend had a V-brake on the front wheel and a
drum-brake on the back wheel. The salesman told me this was for greater reliability in rainy
weather. However, I checked up what John Forrester had to say about this in EFFECTIVE CYCLING.
Although I find his prose really hard to understand, I dimly intuited that he thinks any kind of
brake on the hub, including a drum brake, will fail over more than 750 yard descents because it
cannot evacuate heat sufficiently. I gather he recommends side-pull rim-brakes for this kind of
application. Also he is strongly against unequal configurations on the front and back wheels.

My descent goes on for almost 1.5 km and is _seriously_ steep. So much so that I have not been able
to trust the V-brakes of my cheap-and-cheerful supermarket bike - I walk the bike over this passage
of the trip, both going uphill (because the lowest gear is no low enough) and downhill because I
cannot trust those flimsy brakes with my considerable poundage (I weigh over 200 lb alas). So this
section alone takes up 35% of my travel time although it is only 15% of my distance.

Does this group have opinions on the subject of brakes on steep descents? Is the reliability of the
brakes an important factor in the overall price of a bike? I mean is the cheapness of my current
bike (140 Euros, as opposed to 800 Euros for the Giant) likely to correlate with flimsy brakes, or
is the price of reliable brakes fairly constant over all price ranges? And should I be avoiding drum
brakes like the plague?

Many thanks,

Elisa francesca Roselli Ile de France

 

[Matt J]

Elisa Francesca Roselli asked:
> Although I find his prose really hard to understand, I dimly intuited that he thinks any kind of
> brake on the hub, including a drum brake, will fail over more than 750 yard descents because it
> cannot evacuate heat sufficiently. I gather he recommends side-pull rim-brakes for this kind of
> application. Also he is strongly against unequal configurations on the front and back wheels.
When he implies that any brake on the hub is dangerous for large descents, does he mean only brakes
in the hub (ie drum/drag brakes), or disc brakes too? As far as heat dissipation goes, I believe a
disc brake (one which grabs a steel disc that is bolted to the hub), especially one with an 8" rotor
diameter, will work much better than a rim brake. Additionally, these brakes "fade" less than rim
brakes, and don't affet the tire at all. On a really long/steep descent with rim brakes, it's
possible to blow off tires due to the extreme heat generated from braking.

> I cannot trust those flimsy brakes with my considerable poundage (I weigh over 200 lb alas). So
> this section alone takes up 35% of my travel time although it is only 15% of my distance.
Chances are that your brakes are fine - even very cheap V-Brakes (aka linear pull brakes) work
considerably well, given that they are adjusted properly (that they are tight enough so your lever
doesn't bottom out, and that the pads come in full contact with the rims.)

> I mean is the cheapness of my current bike (140 Euros, as opposed to 800 Euros for the Giant)
> likely to correlate with flimsy brakes, or is the price of reliable brakes fairly constant over
> all price ranges? And should I be avoiding drum brakes like the plague?
Don't think you need to avoid drum brakes like the plague. Rim brakes should be fine for the
situations you describe - especially if they're V-brakes. Even if they're the older "cantilever"
style, as long as they're adjusted properly, they will stop you just fine. If you don't feel
comfortable with rim brakes, consider disc brakes (especially look at the Avid mechanical model).
They have a better "feel" to them, though I doubt they're necessary. For more info, check out
http://sheldonbrown.com/brakes/index.html

Bonne chance! Matt

 

[Elisa Francesca]

Pete wrote:

> Not necessarily bad. After all, you use the front and back completely different. It's just a
> matter of getting used to the differences.

I'm not sure I do use them so differently? When I want to stop, I slam them both on.

> Please tell us your rims are not chrome plated steel, but instead they are made of an alloy (not a
> polished surface).

I have no idea what they are. They are a medium-shiny grey metal. In wet weather the brakes sing
like Wagnerian Valkyries.

> . Inexpensive brakes (drum, V, canti, disc) quite often are built from not too great materials.
> And have a lot of flex. And poor quality pads. Squeeze all you want, and you'll never achieve
> full braking.

I've had the brakes adjusted once already, and have tightened the cable once, but I'm never really
happy with them. I've had the bike for about a year now. I don't know how many kms it's supposed to
deliver before I have to get the pads changed or whatever. There are 314 kms on the computer but I
only installed that about half-way through and it has been reinitialized at least once so that's an
"at least".

> You don't have to spend 800, but 140 may be a bit low.

Well, 800 was the price of the whole bike, which was a nice one with all sorts of attractive
features. This was the brake configuration it came with. Only it was thinking of itself as a comfort
city bike and not one whose daily vocation just happens to include a monster hill. My problem is
that my needs intersect two different and sometimes contradictory idioms of bike. On the one hand,
I'm a sedate middle-aged fat lady who will be using it to cart groceries, on the other the daily
trip to work could soon involve stints fit for a BMX.

> Especially drum on the rear, because you do not use the rear as hard as the front. You DO use the
> front brake more, don't you?

No, I think I use the back brake more - at least it's the one that wears out faster. When braking, I
tend to pull on both brakes about equally, but I don't like the pitchover feeling on the front
brake. Also, the front brake is actioned by the left-hand lever, and the back brake by the
right-hand lever. This means that the back-brake is the one I use whenever I am walking the bike,
since I prefer to walk it on my right side, with my right hand on the handlebars and my left hand
often under the seat. In Contintental Europe that also is the configuration for walking on the left
side of the road, contrary to oncoming traffic. So when I walk it downhill as I described, it's on
the back brake almost all the time.

Elisa Francesca Roselli Ile de France

 

[Brunswick_kate]

Originally posted by Elisa Francesca
You DO use the
> front brake more, don't you?

No, I think I use the back brake more - at least it's the one that wears out faster. When braking, I
tend to pull on both brakes about equally, but I don't like the pitchover feeling on the front
brake. Also, the front brake is actioned by the left-hand lever, and the back brake by the
right-hand lever. This means that the back-brake is the one I use whenever I am walking the bike,
since I prefer to walk it on my right side, with my right hand on the handlebars and my left hand
often under the seat. In Contintental Europe that also is the configuration for walking on the left
side of the road, contrary to oncoming traffic. So when I walk it downhill as I described, it's on
the back brake almost all the time.

Elisa Francesca Roselli Ile de France

Elisa....consider learning a good braking technique for using your front brakes. I converted this summer after reading the Sheldon Brown article

http://www.sheldonbrown.com/brakturn.html and found it made a world of difference. Once you've got it down pat, there is no "flippy factor", which is a good thing. I'm an experienced flipper having bashed myself once 3 times running by using a bad braking techique on a bike with reversed brake cables. The secret is the part about pushing yourself back as you brake. It becomes second nature after a while.

 

[Hunrobe]

>[email protected]

wrote in part:

>I checked up what John Forrester had to say about this in EFFECTIVE CYCLING. Although I find his
>prose really hard to understand, I dimly intuited that he thinks any kind of brake on the hub,
>including a drum brake, will fail over more than 750 yard descents because it cannot evacuate heat
>sufficiently. I gather he recommends side-pull rim-brakes for this kind of application. Also he is
>strongly against unequal configurations on the front and back wheels.
>
>My descent goes on for almost 1.5 km and is _seriously_ steep.

I don't know if they are still operating but for several years there was a bicycle tour company in
Hawaii that offered a "Bike The Crater" package at Mount Haleakala. (Forgive me if I've butchered
that name spelling.) As I recall, that ride is/was a 20+ mile descent with more than a few
"seriously steep" sections. All the bikes they used were equipped with front disc/rear drum brake
combinations.

Regards, Bob Hunt

 

[Jobst Brandt]

Elisa Roselli writes:

> I checked up what John Forester had to say about this in DEFECTIVE CYCLING. Although I find his
> prose really hard to understand, I dimly intuited that he thinks any kind of brake on the hub,
> including a drum brake, will fail over more than 750 yard descents because it cannot evacuate heat
> sufficiently. I gather he recommends side-pull rim-brakes for this kind of application. Also he is
> strongly against unequal configurations on the front and back wheels.

That is a dangerous proposition if you intend to descend mountain roads that require much braking.
Blowing tires off rims is a common ill of tandems. It even occurs on singles if initial inflation
pressure is high. By all means get a hub brake for the rear wheel. Your bicycle shop, if they tour
on tandems, will know which is best.

> My descent goes on for almost 1.5 km and is _seriously_ steep.

> I don't know if they are still operating but for several years there was a bicycle tour company in
> Hawaii that offered a "Bike The Crater" package at Mount Haleakala. I recall, that ride is/was a
> 20+ mile descent with more than a few "seriously steep" sections. All the bikes they used were
> equipped with front disc/rear drum brake combinations.

That is because even a poor hub brake cannot cause a tire blow-off. There is method to that proposal
and it should be heeded. I have been involved in tandem tire blow-off litigation and they involved
injuries. I have blown a tire on my single as have a few of my riding companions, let alone the ones
the bicycle shop can tell about.

Jobst Brandt [email protected]

 

[Paul Hamilton]

There is one tour company in Hawaii that uses Worksman bikes for long mountain descents. These are
very heavy bikes that have front and rear drums. They seem to hold up fine, even under these
conditions.

My bike has front and rear drums, and I appreciate the fact that they work well in the wet, don't
mess up my clothing with black aluminum dust, and require little maintenance. They do have drawbacks
-- one must squeeze harder to get a given amount of braking, and they are heavier. If you detest
doing maintenance and use your bike as a daily commuter/errand runner, they can be ideal.

Paul

 

[Risto Varanka]

I'll throw in my .02 eurocents, not worth much more than that...

Elisa Francesca Roselli <[email protected]> wrote:

: on the front wheel and a drum-brake on the back wheel. The salesman told me this was for greater
: reliability in rainy weather. However, I checked up what John Forrester had to say about this in
: EFFECTIVE CYCLING.

Some research doesn't hurt, hehe

: Although I find his prose really hard to understand, I dimly intuited that he thinks any kind of
: brake on the hub, including a drum brake, will fail over more than 750 yard descents because it
: cannot evacuate heat sufficiently. I gather he recommends side-pull rim-brakes for this kind of
: application. Also he is strongly against unequal configurations on the front and back wheels.

My understanding is that any conventional (rim, disc, drum, etc) braking system has an issue with
heat on long, steep, fast descents. It's not really the type of brake but whether it was designed
for demanding descending applications. Disc brakes are not immune, we had a thread about this in
rec.bicycles.tech in the last few months. As comes to disc brakes, a 200 mm rotor vs a 160 mm one
makes a huge difference. (For us mathematical people, it appears as if the area of the rotor would
almost double.)

You could approach this problem like any engineering one. How steep is the descent and how fast do
you go? The difference between 30 km/h and 70 km/h can be quite significant - although at 70 km/h
you'd get a huge braking effect from aerodynamic drag. Consider the most extreme descending scenario
you intend to ever
do. This will establish how much potential energy is converted into kinetic energy and how much your
braking system needs to convert to thermal energy.

Next you obtain the specs for various braking systems, eg. different kinds of conventional and
heavy-duty brakes, and compare that to your requirements. Well, exact figures are hardly available
so you just do an educated guesstimate and then add a huge margin just to be safe

One cheap system could be a duplicate rear brake, eg. a rim brake and a drum brake on the rear
wheel. You could control the rim brake with a friction lever, so you'd just put it on in the
beginning of the descent, and it would drag just a bit for the complete descent, and in the end
you'd take it off.

: My descent goes on for almost 1.5 km and is _seriously_ steep. So much so that I have not been
: able to trust the V-brakes of my cheap-and-cheerful supermarket bike - I walk the bike over this
: passage of the trip, both going uphill (because the lowest gear is no low enough) and downhill
: because I cannot trust those flimsy brakes with my considerable poundage (I weigh over 200 lb
: alas). So this section alone takes up 35% of my travel time although it is only 15% of my
: distance.

Aha, body weight is a factor as well. (Consider what makes tandems different...)

You probably don't need to walk downhill. If you descend very slowly and use both brakes, there is
no overheating problem. Also, consider that you have two independent braking systems. AFAIK if you
keep both in good shape, the simultaneous failure of both should be extremely rare. Even if both
failed at once, some emergency measures could be taken... though I think any really reasonable
cyclist would just make sure that both of them NEVER fail at the same time. If one of them ever
failed, I'd *definitely* walk the bike down any real hill.

Well that's my .02 on somebody else's descent

--
Risto Varanka | http://www.helsinki.fi/~rvaranka/hpv/hpv.html varis at no spam please iki fi

 

[Bb]

Have you checked out any tandems? Drum brakes aka "drag brakes" are a common option. Set the drum
for a chosen amount of braking and forget it on the descent. Use the hand brakes as usual while
descending. bb

<[email protected]> wrote in message
news:[email protected]...
> I'll throw in my .02 eurocents, not worth much more than that... huge margin just to be
> safe
>
> One cheap system could be a duplicate rear brake, eg. a rim brake and a drum brake on the rear
> wheel. You could control the rim brake with a friction lever, so you'd just put it on in the
> beginning of the descent, and it would drag just a bit for the complete descent, and in the end
> you'd take it off.
> --
> Risto Varanka | http://www.helsinki.fi/~rvaranka/hpv/hpv.html varis at no spam please iki fi

 

[Jobst Brandt]

Risto Varanka writes:

> One cheap system could be a duplicate rear brake, eg. a rim brake and a drum brake on the rear
> wheel. You could control the rim brake with a friction lever, so you'd just put it on in the
> beginning of the descent, and it would drag just a bit for the complete descent, and in the end
> you'd take it off.

Dual rear brakes has been the standard for touring tandems used in the mountains. The hub brake does
the long term speed control while the rim brakes are used to slow down for curves and to supplement
the hub brake if the gradient is steep.

> : My descent goes on for almost 1.5 km and is _seriously_ steep. So
> much : so that I have not been able to trust the V-brakes of my : cheap-and-cheerful supermarket
> bike - I walk the bike over this passage : of the trip, both going uphill (because the lowest gear
> is no low : enough) and downhill because I cannot trust those flimsy brakes with my : considerable
> poundage (I weigh over 200 lb alas). So this section alone : takes up 35% of my travel time
> although it is only 15% of my distance.

It's rim heating that you must watch. The French used to offer insulating rim strips made of a cloth
mesh hose filled with kapok. At the time I saw them offered, I didn't realize why one should use
them but found out later when most of us switched to clinchers from tubulars.

> Aha, body weight is a factor as well. (Consider what makes tandems different...)

> You probably don't need to walk downhill. If you descend very slowly and use both brakes, there is
> no overheating problem.

Not so. At low speeds there is little cooling and much heat buildup. The only time I blew a tire off
the rim was while waiting for a friend on a descent as I crept downhill on the rear brake. I have
never had a problem on that grade because I usually only brake entering hairpin turns, of which
there were many.

> Also, consider that you have two independent braking systems. AFAIK if you keep both in good
> shape, the simultaneous failure of both should be extremely rare. Even if both failed at once,
> some emergency measures could be taken... though I think any really reasonable cyclist would just
> make sure that both of them NEVER fail at the same time. If one of them ever failed, I'd
> *definitely* walk the bike down any real hill.

> Well that's my .02 on somebody else's descent

I think you are hypothesizing rather than working from experience. The real reason for stopping is
if the primary front brake, rim or drum failed. Without a front brake, hard braking is gone on a
single. Descending fast uses primarily the front brake, the rear one being largely ineffective in
any hard braking because it skids so easily. Therefore, the front brake is the most important one to
keep in failsafe maintenance because one cannot afford a front brake failure in fast descending.

http://draco.acs.uci.edu/rbfaq/FAQ/9.15.html

Jobst Brandt [email protected]

 

[Elisa Francesca]

[email protected] wrote:

> You could approach this problem like any engineering one. How steep is the descent and how fast do
> you go? The difference between 30 km/h and 70 km/h can be quite significant - although at 70 km/h
> you'd get a huge braking effect from aerodynamic drag. Consider the most extreme descending
> scenario you intend to ever
> do. This will establish how much potential energy is converted into kinetic energy and how much
> your braking system needs to convert to thermal energy.
>

Good grief, you're blinding me with science. I don't think I'm up to this calculation or it's
application in practical terms. So I go to the shop and ask for so many calories of thermal energy
on my brake system? Somehow I don't think it would pass at my LBS.

> Aha, body weight is a factor as well. (Consider what makes tandems different...)
>

But tandems usually have drum brakes, don't they?

>
> You probably don't need to walk downhill. If you descend very slowly and use both brakes, there is
> no overheating problem.

Now, here's something else I don't understand. I would have thought that the _slower_ I went on the
descent, the _more_ I would have to apply the brakes, and the more friction and heat they would
generate. My notion of brake efficiency is not based on going fast but on going slow: _preventing_
gravity from shooting my mass down that hill way faster than I can control the bike! My maximum
speed to date is 34 kph and I would absolutely _not_ wish to attain this speed on the descent,
indeed, I don't want to do it at more than about 10 kph. In addition to steep, the descent is also
very windey and leaf-strewn, and if I took the curves at speed I would certainly skid.

> Also, consider that you have two independent braking systems. AFAIK if you keep both in good
> shape, the simultaneous failure of both should be extremely rare.

That's a thought. However, I would expect the pitchover effect of a front brake to be accentuated if
I'm already tilting sharply downwards, which is why I'm diffident of relying on a front brake in
this situation.

Elisa Francesca Roselli Ile de France

 

[Elisa Francesca]

[email protected] wrote:

> That is a dangerous proposition if you intend to descend mountain roads that require much braking.
> Blowing tires off rims is a common ill of tandems. It even occurs on singles if initial inflation
> pressure is high. By all means get a hub brake for the rear wheel. Your bicycle shop, if they tour
> on tandems, will know which is best.

I don't understand, what is dangerous, rim or hub brakes? You say that a rim brake can heat the
wheel to the point of blowing off the tyres? But I thought tandems always had hub brakes.

EFR

 

[Elisa Francesca]

At the Paris Cycle Fair, the highest specified bike I saw in the category that interests me
(Cannondale Street 800 Women's) had hydraulic disk brakes by Shimano. These brakes were an important
component in its hefty price tag (nearly 1300 Euros). I was told they are the highest performing
brakes on the market today.

I am interested in a Nexus gear-shifter of the type that can be shifted when you are at a
standstill. This shifter is available for 3, 4 and 7 speeds. But from what I understand (through a
glass darkly, as the Shimano brochure is written in Parseltongue ....) this kind of shifter
_requires_ a hub-brake on the rear wheel. It can be paired with a drum brake (as on the Giant
Melbourne which is also on my list of candidates), a disk brake or a back-pedalling system. Of
these, the most expensive is the hydraulic disk brake.

So is this luxury brake the one to rely on for long steep descents? What are the reasons for its
high price?

Elisa Francesca Roselli Ile de France

 

[David Kerber]

In article <[email protected]>,
[email protected] says...
>
>
> [email protected] wrote:
>
> > You could approach this problem like any engineering one. How steep is the descent and how fast
> > do you go? The difference between 30 km/h and 70 km/h can be quite significant - although at 70
> > km/h you'd get a huge braking effect from aerodynamic drag. Consider the most extreme descending
> > scenario you intend to ever
> > do. This will establish how much potential energy is converted into kinetic energy and how much
> > your braking system needs to convert to thermal energy.
> >
>
> Good grief, you're blinding me with science. I don't think I'm up to this calculation or it's
> application in practical terms. So I go to the shop and ask for so many calories of thermal energy
> on my brake system? Somehow I don't think it would pass at my LBS.
>
> > Aha, body weight is a factor as well. (Consider what makes tandems different...)
> >
>
> But tandems usually have drum brakes, don't they?
>
> >
> > You probably don't need to walk downhill. If you descend very slowly and use both brakes, there
> > is no overheating problem.
>
> Now, here's something else I don't understand. I would have thought that the _slower_ I went on
> the descent, the _more_ I would have to apply the brakes, and the more friction and heat they
> would generate. My notion of brake efficiency is

It depends on how fast you are going. If you are holding the brakes hard enough to only go 1 or 2
kph, they won't get very hot because there is lots of time to dissipate heat, and if you are going
30+ not using the brakes they obviously won't get hot. The max heat generation is somewhere between
these two extremes.

> not based on going fast but on going slow: _preventing_ gravity from shooting my mass down that
> hill way faster than I can control the bike! My maximum speed to date is 34 kph and I would
> absolutely _not_ wish to attain this speed on the descent, indeed, I don't want to do it at more
> than about 10 kph. In addition to steep, the descent is also very windey and leaf-strewn, and if I
> took the curves at speed I would certainly skid.
>
> > Also, consider that you have two independent braking systems. AFAIK if you keep both in good
> > shape, the simultaneous failure of both should be extremely rare.
>
> That's a thought. However, I would expect the pitchover effect of a front brake to be accentuated
> if I'm already tilting sharply downwards, which is why I'm diffident of relying on a front brake
> in this situation.

Few hills are actually steep enough for this to be a significant factor in how easy it is to pitch
your bike over the front wheel, even though it might feel like it.

--
Dave Kerber Fight spam: remove the ns_ from the return address before replying!

REAL programmers write self-modifying code.

 

[Risto Varanka]

David Kerber <ns_dkerber@ns_ids.net> wrote:

: It depends on how fast you are going. If you are holding the brakes hard enough to only go 1 or 2
: kph, they won't get very hot because there is lots of time to dissipate heat, and if you are going
: 30+ not using the brakes they obviously won't get hot. The max heat generation is somewhere
: between these two extremes.

I thought we were talking the extreme where you have to do constant and significant braking just to
keep from going faster than the 30 km/h.

If you go faster, you lose altitude at a greater rate, ie. you convert potential energy to kinetic
at a greater rate. To me this would appear to mean that you need to apply the brakes more, in order
to control the resulting acceleration.

--
Risto Varanka | http://www.helsinki.fi/~rvaranka/hpv/hpv.html varis at no spam please iki fi

 

[Jobst Brandt]

Elisa Francesca Roselli writes:

>> That is a dangerous proposition if you intend to descend mountain roads that require much
>> braking. Blowing tires off rims is a common ill of tandems. It even occurs on singles if initial
>> inflation pressure is high. By all means get a hub brake for the rear wheel. Your bicycle shop,
>> if they tour on tandems, will know which is best.

> I don't understand, what is dangerous, rim or hub brakes? You say that a rim brake can heat the
> wheel to the point of blowing off the tyres? But I thought tandems always had hub brakes.

They don't!

Jobst Brandt [email protected]

 

[David Kerber]

In article <[email protected]>,
[email protected] says...
> David Kerber <ns_dkerber@ns_ids.net> wrote:
>
> : It depends on how fast you are going. If you are holding the brakes hard enough to only go 1 or
> : 2 kph, they won't get very hot because there is lots of time to dissipate heat, and if you are
> : going 30+ not using the brakes they obviously won't get hot. The max heat generation is
> : somewhere between these two extremes.
>
> I thought we were talking the extreme where you have to do constant and significant braking just
> to keep from going faster than the 30 km/h.
>
> If you go faster, you lose altitude at a greater rate, ie. you convert potential energy to kinetic
> at a greater rate. To me this would appear to mean that you need to apply the brakes more, in
> order to control the resulting acceleration.

If you have to apply the brakes relatively hard just to keep below 30, then yes, you definitely have
to worry about heat buildup. Also, I was thinking of 30+ mph, not kph. That's just a difference in
degree, not kind, though.

However, the point that going VERY slowly won't overheat your brakes still applies. Your hand will
likely give out first.

--
Dave Kerber Fight spam: remove the ns_ from the return address before replying!

REAL programmers write self-modifying code.