Brakes

On 12/7/2015 9:39 PM, John B. wrote:
On Tue, 8 Dec 2015 11:59:02 +1000, James
wrote:

On 08/12/15 11:28, Frank Krygowski wrote:
On 12/7/2015 8:03 PM, John B. wrote:

I am presently assembling the new (old) bike and find that I need
"special" brakes for it as it is old enough to have ~55mm brakes and
the ones that were on the bike when I bought the bike are in very poor
condition.

In looking for replacement brakes I find quite a number that will work
and am wondering whether there is really a difference between single
and double pivot caliper brakes, as I have found some Dia-Comp single
pivot brakes that are in almost new condition and fit the period in
which the bike was made.

Dual pivot brakes will probably have a significantly higher mechanical
advantage. With single pivot brakes, you'll have to squeeze harder for
the same deceleration. OTOH, they'll provide more lateral clearance
when open, so less chance of rubbing if your wheel's a bit out of true,
providing they're well centered.

There's this: http://sheldonbrown.com/brandt/brakes.html
and this: http://sheldonbrown.com/calipers.html



Significantly higher? I'm not sure how significant.

Exactly. If I'm doing 60 KPH down Big Mountain Hill will the dual
pivot brake actually stop me quicker then the single pivot. A lot
quicker?

Frankly I notice considerable difference in braking due to brake pad
material but less between, say, cantilever and caliper.
--

Cheers,

John B.


And there's the difference between new pads and old hard
dried pads with chunks of gravel and rim in them...

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

On 12/7/2015 10:35 PM, John B. wrote:
On Mon, 7 Dec 2015 20:28:40 -0500, Frank Krygowski wrote:


Dual pivot brakes will probably have a significantly higher mechanical
advantage. With single pivot brakes, you'll have to squeeze harder for
the same deceleration. OTOH, they'll provide more lateral clearance
when open, so less chance of rubbing if your wheel's a bit out of true,
providing they're well centered.

There's this: http://sheldonbrown.com/brandt/brakes.html
and this: http://sheldonbrown.com/calipers.html

But, is the higher mechanical advantage significant, in the sense that
one type actually stops better, or faster, then the other. Or perhaps
"is one safer then the other?" to appease those with broken straddle
cables :-)

I don't think the higher mechanical advantage causes faster stops. With
decent brake blocks, either brake type delivers stops that are fast
enough to throw you over the bars, which is the practical limit. You
just have to squeeze a bit harder with single pivot brakes.

I'll note, though, that there's a compounding effect that's not widely
recognized. If the cable tension at the brake is less by (say) 30%, the
force at the lever is reduced an even greater amount. This is because
friction is always present around every bend in the cable, which sort of
amplifies any difference. T1/T2 = e^(mu*theta)
http://www.answers.com/Q/How_to_find..._around_circle

Personally, I prefer brakes that require a bit more hand pressure. I
still remember the power brakes on my dad's 1959 Pontiac. It seemed you
could lock the four wheels with a light touch - not very controllable.

In one cycling class I taught, a not-very-bright beginner showed up with
the bike her boyfriend had just lent to her. It had dual pivot brakes,
and she definitely was not used to the lower hand force. On her first
excursion across the parking lot, she locked up the front wheel and went
over the bars.

Perhaps because of those sorts of incidents, Shimano has put brake
limiting spring devices into the front brake cables of some comfort
bikes with V-brakes. Seems a bit weird to build a super-strong brake,
then sort of cripple it, but I guess there are reasons.

--
- Frank Krygowski

On Monday, December 7, 2015 at 8:41:28 PM UTC-8, Sir Ridesalot wrote:
On Monday, December 7, 2015 at 11:13:02 PM UTC-5, jbeattie wrote:
On Monday, December 7, 2015 at 5:03:34 PM UTC-8, John B. wrote:
I am presently assembling the new (old) bike and find that I need
"special" brakes for it as it is old enough to have ~55mm brakes and
the ones that were on the bike when I bought the bike are in very poor
condition.

In looking for replacement brakes I find quite a number that will work
and am wondering whether there is really a difference between single
and double pivot caliper brakes, as I have found some Dia-Comp single
pivot brakes that are in almost new condition and fit the period in
which the bike was made.

comments?
--
cheers,

John B.

I much prefer the light feel of dual pivots. Any quality brake will stop your bike -- except Modolo Kronos or Delta-ish type brakes.

-- Jay Beattie.

My Dura Ace AX barke calipers do an excellent job of stopping the bicycle they're on and that even with the rather small brake blocks they use.

Cheers

Different design than Delta or Kronos. The Kronos had tiny calipers, too. http://www.classicrendezvous.com/Ita...olo_Kronos.htm I think the Shimano brakes were more mechanically sound.

-- Jay Beattie.

Frank Krygowski wrote:

:Personally, I prefer brakes that require a bit more hand pressure. I
:still remember the power brakes on my dad's 1959 Pontiac. It seemed you
:could lock the four wheels with a light touch - not very controllable.

Probably had drum brakes. Drums have shoes that, in one direction,
tend to pull themselves into the drums, reducing the force needed to
apply them. With power brakes, it's very easy to apply too much
intial force and lock a wheel.

--
sig 48

On 08/12/15 18:42, Frank Krygowski wrote:

snip

Perhaps because of those sorts of incidents, Shimano has put brake
limiting spring devices into the front brake cables of some comfort
bikes with V-brakes. Seems a bit weird to build a super-strong brake,
then sort of cripple it, but I guess there are reasons.

These are the work of Stan. If you don't want to go over the
handlebars, use less fingers or more sense.

On 12/8/2015 10:46 AM, David Scheidt wrote:
Frank Krygowski wrote:

:Personally, I prefer brakes that require a bit more hand pressure. I
:still remember the power brakes on my dad's 1959 Pontiac. It seemed you
:could lock the four wheels with a light touch - not very controllable.

Probably had drum brakes. Drums have shoes that, in one direction,
tend to pull themselves into the drums, reducing the force needed to
apply them. With power brakes, it's very easy to apply too much
intial force and lock a wheel.

Yes, early power brakes were all drum brakes. They were really touchy.

Nowadays, the only drum brakes on new cars are the parking brakes,
though there may be some low end vehicles that still do front discs and
rear drums.

On 12/8/2015 11:16 AM, Tosspot wrote:
On 08/12/15 18:42, Frank Krygowski wrote:

snip

Perhaps because of those sorts of incidents, Shimano has put brake
limiting spring devices into the front brake cables of some comfort
bikes with V-brakes. Seems a bit weird to build a super-strong brake,
then sort of cripple it, but I guess there are reasons.

These are the work of Stan. If you don't want to go over the
handlebars, use less fingers or more sense.

Who is Stan?

But it makes sense to prevent cyclist from serious injuries by reducing
the likelihood of locking up a wheel and being thrown over the handlebars.

On Tuesday, December 8, 2015 at 11:34:09 AM UTC-8, sms wrote:
On 12/8/2015 11:16 AM, Tosspot wrote:
On 08/12/15 18:42, Frank Krygowski wrote:

snip

Perhaps because of those sorts of incidents, Shimano has put brake
limiting spring devices into the front brake cables of some comfort
bikes with V-brakes. Seems a bit weird to build a super-strong brake,
then sort of cripple it, but I guess there are reasons.

These are the work of Stan. If you don't want to go over the
handlebars, use less fingers or more sense.

Who is Stan?

But it makes sense to prevent cyclist from serious injuries by reducing
the likelihood of locking up a wheel and being thrown over the handlebars.

Unfortunately bicycle rim brakes tend to get dirty and wet and then work like ****

On 12/8/2015 12:19 PM, Doug Landau wrote:
On Tuesday, December 8, 2015 at 11:34:09 AM UTC-8, sms wrote:
On 12/8/2015 11:16 AM, Tosspot wrote:
On 08/12/15 18:42, Frank Krygowski wrote:

snip

Perhaps because of those sorts of incidents, Shimano has put brake
limiting spring devices into the front brake cables of some comfort
bikes with V-brakes. Seems a bit weird to build a super-strong brake,
then sort of cripple it, but I guess there are reasons.

These are the work of Stan. If you don't want to go over the
handlebars, use less fingers or more sense.

Who is Stan?

But it makes sense to prevent cyclist from serious injuries by reducing
the likelihood of locking up a wheel and being thrown over the handlebars.

Unfortunately bicycle rim brakes tend to get dirty and wet and then work like ****

A lot of riders, and I know one personally, are so used to rim brakes
that "work like ****" that when they are provided with a bicycle with
powerful, effective, brakes, are injured when they lock up the front
wheel. It makes sense for Shimano to take steps to prevent this sort of
thing.

But it makes sense to prevent cyclist from serious injuries by reducing
the likelihood of locking up a wheel and being thrown over the handlebars.

Unfortunately bicycle rim brakes tend to get dirty and wet and then work like ****

A lot of riders, and I know one personally, are so used to rim brakes
that "work like ****" that when they are provided with a bicycle with
powerful, effective, brakes, are injured when they lock up the front
wheel. It makes sense for Shimano to take steps to prevent this sort of
thing.

I know this will draw a volley of "not me!" responses, but I imagine that most cyclists must be used to them working like ****, because how well they work goes off so quickly.

When I clean my bike, I clean the rims with soap+water followed by rubbing alcohol, clean the pads with rubbing alcohol, and then hit the brake pads lightly with sandpaper to remove the glaze and expose a fresh surface. They work like new after that ... nice and grabby ... but not for long. The grabbiness is gone very quickly and I don't notice how much weaker they are until I clean the bike again a week or two later.

I think it makes more sense for shimano to provide a brake that works when wet and dirty as wet happens and dirty is their usual condition, across most cyclists. Their first responsibility is to provide something usable, and the range of how well they work from freshly cleaned to dirty in the rain downhill is so wide that if calibrated to work in the latter condition, they will be subject to the "too scrong" criticism in the former.