Brake question

Robin Hubert said:

What my be the source of different braking power on two bikes? One bike
has Dura Ace single pivot short reach brakes with Tektro cartridge
pads/stock inserts, squeezed by Ergo levers. On this bike I can fairly
easily raise the rear wheel.

The other has Suntour Superbe single pivot, long reach, same pads,
Shimano R600 brake levers. I have to squeeze the heck out of the levers
on this bike to haul it down adequately.

The bike with the long reach brakes has a rim (Sun CR18) that is 22.5mm
wide, while the other (Mavic CXP30) has a 19.6mm rim width. Neither
rim is hard anodized. The machined grooves on the Mavic rim are long
gone, and the Sun rim has a brushed finish with less than 500 miles.

Thanks for your thoughts.

Robin Hubert

Dear Robin,

Could it be the leverage of long versus short reach arms?

Carl Fogel

Robin Hubert asked:

Quoted message said:

What my be the source of different braking power on two bikes? One bike
has Dura Ace single pivot short reach brakes with Tektro cartridge
pads/stock inserts, squeezed by Ergo levers. On this bike I can fairly
easily raise the rear wheel.

The other has Suntour Superbe single pivot, long reach, same pads,
Shimano R600 brake levers. I have to squeeze the heck out of the levers
on this bike to haul it down adequately.

A single pivot brake caliper is a simple lever, basically the same as a
pair of pliers with a bend in the middle.

The mechanical advantage is determined by the ratio of two distances:

•A. The shortest distance from the pivot axis to the cable.

•B. The distance from the pivot axis to the brake shoe/rim (i.e., the
reach.)

Well designed sidepulls should increase distance "A" for models with
longer reach. Unfortunately this doesn't always happen.

My guess is that your calipers have similar "A" distances, but the
longer reach on the Sun Tour calipers reduces the mechanical advantage.

Note that the "B" dimension will vary according to where you need to set
the brake shoe in its mounting slot. Thus the same caliper will have
higher mechanical advantage if the shoe is set near the top of the slot
than it does with the shoe at the bottom.

That's why bikes that have been converted from 630 mm (27"😉 wheels to
622 mm (700C) often lose some braking power.

Sheldon "Leverage" Brown
+--------------------------------------------------+
| Whoever you vote for, the government gets in. |
| John Jones--Oysterband |
+--------------------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

Robin Hubert said:

What my be the source of different braking power on two bikes? One
bike has Dura Ace single pivot short reach brakes with Tektro
cartridge pads/stock inserts, squeezed by Ergo levers. On this bike
I can fairly easily raise the rear wheel.

The other has Suntour Superbe single pivot, long reach, same pads,
Shimano R600 brake levers. I have to squeeze the heck out of the
levers on this bike to haul it down adequately.

The bike with the long reach brakes has a rim (Sun CR18) that is
22.5mm wide, while the other (Mavic CXP30) has a 19.6mm rim width.
Neither rim is hard anodized. The machined grooves on the Mavic rim
are long gone, and the Sun rim has a brushed finish with less than
500 miles.

There are so many factors in braking that's it's hard to pin a problem
down. Braking surface is one factor, but the size, shape and weight of
the bike is a bigger one, I think, especially if the riding positions are
different as well.

~PB

Robin Hubert said:

What my be the source of different braking power on two bikes? One bike
has Dura Ace single pivot short reach brakes with Tektro cartridge
pads/stock inserts, squeezed by Ergo levers. On this bike I can fairly
easily raise the rear wheel.

The other has Suntour Superbe single pivot, long reach, same pads,
Shimano R600 brake levers. I have to squeeze the heck out of the levers
on this bike to haul it down adequately.

The bike with the long reach brakes has a rim (Sun CR18) that is 22.5mm
wide, while the other (Mavic CXP30) has a 19.6mm rim width. Neither
rim is hard anodized. The machined grooves on the Mavic rim are long
gone, and the Sun rim has a brushed finish with less than 500 miles.

It's a bad match of lever and caliper; V-brake levers and cantilever
brakes are another example that feels firm but requires unreasonable
hand force to stop.

Your R600 levers are designed for dual-pivot brakes wiuth a high
mechanical advantage (halfway to V brakes) and the Superbe brakes don't
have this.

Robin Hubert said:

What my be the source of different braking power on two bikes? One
bike has Dura Ace single pivot short reach brakes with Tektro
cartridge pads/stock inserts, squeezed by Ergo levers. On this bike
I can fairly easily raise the rear wheel.

Quoted message said:

The other has SunTour Superbe single pivot, long reach, same pads,
Shimano R600 brake levers. I have to squeeze the heck out of the
levers on this bike to haul it down adequately.

Quoted message said:

The bike with the long reach brakes has a rim (Sun CR18) that is
22.5mm wide, while the other (Mavic CXP30) has a 19.6mm rim width.
Neither rim is hard anodized. The machined grooves on the Mavic rim
are long gone, and the Sun rim has a brushed finish with less than
500 miles.

Nearly all single pivot brakes have a mechanical advantage (ME) of 1:1
while nearly all hand levers have a ratio of 4:1. When complaints of
too high demands on rider's grip were addressed it became apparent
that the poor centering of single pivot brakes would not allow
increasing the ME because that required reducing pad clearance. Pad
clearance taken up by a higher ME caliper would use up the lever
stroke before giving significant braking.

To improve brake centering the dual pivot brake was introduced (it had
been around for a while anyway) to increase ME which, as far as I can
measure in the bicycle shop is about 5.6:1. I think that is where the
difference in your braking lies.

The higher ME of dual pivot brakes does not come without its demerits.
If the QR is inadvertently left open after inserting a wheel, the
brake has practically no effect, certainly far less than a single
pivot brake whose QR is left open... and the brake pad from the offset
pivot climbs into the tire as it wears, requiring brake adjustment to
prevent cutting the casing. This second effect is only a problem for
people who ride many steep mountain roads, especially when not using
Kool Stop salmon pads that wear less than half as fast as most major
brands.

It is for this reason that Campagnolo re-introduced a single pivot
rear brake that can run with larger pad clearance to not drag when
climbing out of the saddle, the impetus for this design change.

http://www.sheldonbrown.com/brandt/brakes.html

Jobst Brandt
[email hidden]

Robin Hubert said:

Quoted message said:

What my be the source of different braking power on two bikes? One
bike has Dura Ace single pivot short reach brakes with Tektro
cartridge pads/stock inserts, squeezed by Ergo levers. On this bike I
can fairly easily raise the rear wheel.

The other has Suntour Superbe single pivot, long reach, same pads,
Shimano R600 brake levers. I have to squeeze the heck out of the
levers on this bike to haul it down adequately.

The bike with the long reach brakes has a rim (Sun CR18) that is
22.5mm wide, while the other (Mavic CXP30) has a 19.6mm rim width.
Neither rim is hard anodized. The machined grooves on the Mavic rim
are long gone, and the Sun rim has a brushed finish with less than 500
miles.

I answered this in a previous posting.

A usually reliable source replied with a popular error:

Quoted message said:

It's a bad match of lever and caliper; V-brake levers and cantilever
brakes are another example that feels firm but requires unreasonable
hand force to stop.

Your R600 levers are designed for dual-pivot brakes wiuth a high
mechanical advantage (halfway to V brakes) and the Superbe brakes don't
have this.

That's false.

The R600 levers have essentially the same mechanical advantage as the
Ergos, all "aero" type levers have pretty much the same mechanical
advantage, with the exception of a couple of Dia Compe models.

"Aero" brake levers actually have slightly _higher_ mechanical advantage
than the old-fashioned levers that had the cables exiting the top of the
hood. That's one of the reasons they're superior to the old type.

Far from being a mismatch, installing modern "aero" brake levers is one
of the best ways to upgrade older brake systems.

Sheldon "Myths Die Hard" Brown
+--------------------------------------------+
| All the world's a stage and most of us |
| are desperately unrehearsed. |
| --Sean O'Casey |
+--------------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

Robin Hubert said:

What my be the source of different braking power on two bikes? One bike
has Dura Ace single pivot short reach brakes with Tektro cartridge
pads/stock inserts, squeezed by Ergo levers. On this bike I can fairly
easily raise the rear wheel.

The other has Suntour Superbe single pivot, long reach, same pads,
Shimano R600 brake levers. I have to squeeze the heck out of the levers
on this bike to haul it down adequately.

The bike with the long reach brakes has a rim (Sun CR18) that is 22.5mm
wide, while the other (Mavic CXP30) has a 19.6mm rim width. Neither
rim is hard anodized. The machined grooves on the Mavic rim are long
gone, and the Sun rim has a brushed finish with less than 500 miles.

I'm pretty sure you have roughly identical leverage at the
lever and from the wire/casing inputs to the brake pivots
but you're moving either 35mm from the pivot to the pad or
58mm which _should_ be different!

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

Quoted message said:

Robin Hubert said:

What my be the source of different braking power on two bikes? One
bike has Dura Ace single pivot short reach brakes with Tektro

^^^^^^^^^^^^^^^^^^^^^^^^

Quoted message said:

Quoted message said:

cartridge pads/stock inserts, squeezed by Ergo levers. On this bike
I can fairly easily raise the rear wheel.

Quoted message said:

The other has SunTour Superbe single pivot, long reach, same pads,

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Quoted message said:

Quoted message said:

Shimano R600 brake levers. I have to squeeze the heck out of the
levers on this bike to haul it down adequately.

Quoted message said:

The bike with the long reach brakes has a rim (Sun CR18) that is
22.5mm wide, while the other (Mavic CXP30) has a 19.6mm rim width.
Neither rim is hard anodized. The machined grooves on the Mavic rim
are long gone, and the Sun rim has a brushed finish with less than
500 miles.

Nearly all single pivot brakes have a mechanical advantage (ME) of 1:1
while nearly all hand levers have a ratio of 4:1. When complaints of
too high demands on rider's grip were addressed it became apparent
that the poor centering of single pivot brakes would not allow
increasing the ME because that required reducing pad clearance. Pad
clearance taken up by a higher ME caliper would use up the lever
stroke before giving significant braking.

To improve brake centering the dual pivot brake was introduced (it had
been around for a while anyway) to increase ME which, as far as I can
measure in the bicycle shop is about 5.6:1. I think that is where the
difference in your braking lies.

The higher ME of dual pivot brakes does not come without its demerits.
If the QR is inadvertently left open after inserting a wheel, the
brake has practically no effect, certainly far less than a single
pivot brake whose QR is left open... and the brake pad from the offset
pivot climbs into the tire as it wears, requiring brake adjustment to
prevent cutting the casing. This second effect is only a problem for
people who ride many steep mountain roads, especially when not using
Kool Stop salmon pads that wear less than half as fast as most major
brands.

It is for this reason that Campagnolo re-introduced a single pivot
rear brake that can run with larger pad clearance to not drag when
climbing out of the saddle, the impetus for this design change.

http://www.sheldonbrown.com/brandt/brakes.html

Jobst Brandt
[email hidden]

Dear Jobst,

The original post says that both brakes are single pivot.

Isn't it more likely that the different mechanical advantage
of the short and the long reach arms explains the difference
in how hard he has to squeeze?

Carl Fogel

Quoted message said:

Quoted message said:

Robin Hubert said:

What my be the source of different braking power on two bikes? One
bike has Dura Ace single pivot short reach brakes with Tektro

^^^^^^^^^^^^^^^^^^^^^^^^

Quoted message said:

Quoted message said:

cartridge pads/stock inserts, squeezed by Ergo levers. On this bike
I can fairly easily raise the rear wheel.

Quoted message said:

The other has SunTour Superbe single pivot, long reach, same pads,

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Quoted message said:

Quoted message said:

Shimano R600 brake levers. I have to squeeze the heck out of the
levers on this bike to haul it down adequately.

Quoted message said:

The bike with the long reach brakes has a rim (Sun CR18) that is
22.5mm wide, while the other (Mavic CXP30) has a 19.6mm rim width.
Neither rim is hard anodized. The machined grooves on the Mavic rim
are long gone, and the Sun rim has a brushed finish with less than
500 miles.

Nearly all single pivot brakes have a mechanical advantage (ME) of 1:1
while nearly all hand levers have a ratio of 4:1. When complaints of
too high demands on rider's grip were addressed it became apparent
that the poor centering of single pivot brakes would not allow
increasing the ME because that required reducing pad clearance. Pad
clearance taken up by a higher ME caliper would use up the lever
stroke before giving significant braking.

To improve brake centering the dual pivot brake was introduced (it had
been around for a while anyway) to increase ME which, as far as I can
measure in the bicycle shop is about 5.6:1. I think that is where the
difference in your braking lies.

The higher ME of dual pivot brakes does not come without its demerits.
If the QR is inadvertently left open after inserting a wheel, the
brake has practically no effect, certainly far less than a single
pivot brake whose QR is left open... and the brake pad from the offset
pivot climbs into the tire as it wears, requiring brake adjustment to
prevent cutting the casing. This second effect is only a problem for
people who ride many steep mountain roads, especially when not using
Kool Stop salmon pads that wear less than half as fast as most major
brands.

It is for this reason that Campagnolo re-introduced a single pivot
rear brake that can run with larger pad clearance to not drag when
climbing out of the saddle, the impetus for this design change.

http://www.sheldonbrown.com/brandt/brakes.html

Jobst Brandt
[email hidden]

Dear Jobst,

The original post says that both brakes are single pivot.

Isn't it more likely that the different mechanical advantage
of the short and the long reach arms explains the difference
in how hard he has to squeeze?

Carl Fogel

The difference happens to be 4-5mm. FWIW, both levers are supposedly
designed to work with dual pivot brakes.

Robin Hubert

Jobst Brandt said:

The higher ME of dual pivot brakes does not come without its demerits.

Quoted message said:

If the QR is inadvertently left open after inserting a wheel, the
brake has practically no effect, certainly far less than a single
pivot brake whose QR is left open... (snip)

Not since 1991 (per link below) with Campagnolo:

<http://www.branfordbike.com/brake/brk04.html>

Safer both because the brakes always work full force, QR's open or
closed, and no hands off bars (near spinning wheels) needed to operate
these on the fly. --TP

Robin Hubert said:

Quoted message said:

Quoted message said:

Robin Hubert writes:

>What my be the source of different braking power on two bikes? One
>bike has Dura Ace single pivot short reach brakes with Tektro

^^^^^^^^^^^^^^^^^^^^^^^^

Quoted message said:

>cartridge pads/stock inserts, squeezed by Ergo levers. On this bike
>I can fairly easily raise the rear wheel.

>The other has SunTour Superbe single pivot, long reach, same pads,

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Quoted message said:

>Shimano R600 brake levers. I have to squeeze the heck out of the
>levers on this bike to haul it down adequately.

>The bike with the long reach brakes has a rim (Sun CR18) that is
>22.5mm wide, while the other (Mavic CXP30) has a 19.6mm rim width.
>Neither rim is hard anodized. The machined grooves on the Mavic rim
>are long gone, and the Sun rim has a brushed finish with less than
>500 miles.

Nearly all single pivot brakes have a mechanical advantage (ME) of 1:1
while nearly all hand levers have a ratio of 4:1. When complaints of
too high demands on rider's grip were addressed it became apparent
that the poor centering of single pivot brakes would not allow
increasing the ME because that required reducing pad clearance. Pad
clearance taken up by a higher ME caliper would use up the lever
stroke before giving significant braking.

To improve brake centering the dual pivot brake was introduced (it had
been around for a while anyway) to increase ME which, as far as I can
measure in the bicycle shop is about 5.6:1. I think that is where the
difference in your braking lies.

The higher ME of dual pivot brakes does not come without its demerits.
If the QR is inadvertently left open after inserting a wheel, the
brake has practically no effect, certainly far less than a single
pivot brake whose QR is left open... and the brake pad from the offset
pivot climbs into the tire as it wears, requiring brake adjustment to
prevent cutting the casing. This second effect is only a problem for
people who ride many steep mountain roads, especially when not using
Kool Stop salmon pads that wear less than half as fast as most major
brands.

It is for this reason that Campagnolo re-introduced a single pivot
rear brake that can run with larger pad clearance to not drag when
climbing out of the saddle, the impetus for this design change.

http://www.sheldonbrown.com/brandt/brakes.html

Jobst Brandt
[email hidden]

Dear Jobst,

The original post says that both brakes are single pivot.

Isn't it more likely that the different mechanical advantage
of the short and the long reach arms explains the difference
in how hard he has to squeeze?

Carl Fogel

The difference happens to be 4-5mm. FWIW, both levers are supposedly
designed to work with dual pivot brakes.

Robin Hubert

Dear Robin,

Can you measure the arms in a few dimensions?

That is, what are the distances from the middle of the brake
pad to the pivot and from the pivot to where the cable
action is applied?

With those, we could work out the actual mechanical
advantage--the difference alone at one point isn't enough.

Long reach pad to pivot: xx mm
Long reach pivot to cable: xx mm

Short reach pad to pivot: xx mm
Short reach pivot to cable: xx mm

The leverage may not be the culprit, but you seem to be
saying that everything is about the same except that one
rear brake is a short reach and the other is a long reach.

Carl Fogel

Quoted message said:

Robin Hubert said:

Quoted message said:

On Sun, 27 Feb 2005 22:41:49 GMT,
[email hidden] wrote:

>Robin Hubert writes:
>
>
>
>>What my be the source of different braking power on two bikes? One
>>bike has Dura Ace single pivot short reach brakes with Tektro

^^^^^^^^^^^^^^^^^^^^^^^^

>>cartridge pads/stock inserts, squeezed by Ergo levers. On this bike
>>I can fairly easily raise the rear wheel.
>
>>The other has SunTour Superbe single pivot, long reach, same pads,

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

>>Shimano R600 brake levers. I have to squeeze the heck out of the
>>levers on this bike to haul it down adequately.
>
>>The bike with the long reach brakes has a rim (Sun CR18) that is
>>22.5mm wide, while the other (Mavic CXP30) has a 19.6mm rim width.
>>Neither rim is hard anodized. The machined grooves on the Mavic rim
>>are long gone, and the Sun rim has a brushed finish with less than
>>500 miles.
>
>Nearly all single pivot brakes have a mechanical advantage (ME) of 1:1
>while nearly all hand levers have a ratio of 4:1. When complaints of
>too high demands on rider's grip were addressed it became apparent
>that the poor centering of single pivot brakes would not allow
>increasing the ME because that required reducing pad clearance. Pad
>clearance taken up by a higher ME caliper would use up the lever
>stroke before giving significant braking.
>
>To improve brake centering the dual pivot brake was introduced (it had
>been around for a while anyway) to increase ME which, as far as I can
>measure in the bicycle shop is about 5.6:1. I think that is where the
>difference in your braking lies.
>
>The higher ME of dual pivot brakes does not come without its demerits.
>If the QR is inadvertently left open after inserting a wheel, the
>brake has practically no effect, certainly far less than a single
>pivot brake whose QR is left open... and the brake pad from the offset
>pivot climbs into the tire as it wears, requiring brake adjustment to
>prevent cutting the casing. This second effect is only a problem for
>people who ride many steep mountain roads, especially when not using
>Kool Stop salmon pads that wear less than half as fast as most major
>brands.
>
>It is for this reason that Campagnolo re-introduced a single pivot
>rear brake that can run with larger pad clearance to not drag when
>climbing out of the saddle, the impetus for this design change.
>
>http://www.sheldonbrown.com/brandt/brakes.html
>
>Jobst Brandt
>[email hidden]

Dear Jobst,

The original post says that both brakes are single pivot.

Isn't it more likely that the different mechanical advantage
of the short and the long reach arms explains the difference
in how hard he has to squeeze?

Carl Fogel

The difference happens to be 4-5mm. FWIW, both levers are supposedly
designed to work with dual pivot brakes.

Robin Hubert

Dear Robin,

Can you measure the arms in a few dimensions?

That is, what are the distances from the middle of the brake
pad to the pivot and from the pivot to where the cable
action is applied?

With those, we could work out the actual mechanical
advantage--the difference alone at one point isn't enough.

Long reach pad to pivot: xx mm
Long reach pivot to cable: xx mm

Short reach pad to pivot: xx mm
Short reach pivot to cable: xx mm

The leverage may not be the culprit, but you seem to be
saying that everything is about the same except that one
rear brake is a short reach and the other is a long reach.

Carl Fogel

Hi Carl,

These are measurments from the pads.
74/53mm for the long reach, and 80/49mm for the short reach. I reckon
the pivot to cable (which I take to mean the top of the arm at the bbl
adjuster) can be exrapolated from the above to 21mm and 31mm
respectively (I hesitate to run downstairs again).

Is this the information you're looking for?

Thanks,
Robin Hubert

Robin Hubert wrote:
Carl Fogel asked:

Quoted message said:

Quoted message said:

Dear Robin,

Can you measure the arms in a few dimensions?

That is, what are the distances from the middle of the brake
pad to the pivot and from the pivot to where the cable
action is applied?

With those, we could work out the actual mechanical
advantage--the difference alone at one point isn't enough.

Long reach pad to pivot: xx mm
Long reach pivot to cable: xx mm

Short reach pad to pivot: xx mm
Short reach pivot to cable: xx mm

The leverage may not be the culprit, but you seem to be
saying that everything is about the same except that one
rear brake is a short reach and the other is a long reach.

Robin Hubert replied:

Quoted message said:

Hi Carl,

These are measurments from the pads.
74/53mm for the long reach, and 80/49mm for the short reach.

The range of adjustability of the pads is not relevant. What counts is
the actual reach to the pad when it is adjusted to to reach the rim in
your particular installation.

See: http://sheldonbrown.com/reach

Quoted message said:

I reckon
the pivot to cable (which I take to mean the top of the arm at the bbl
adjuster) can be exrapolated from the above to 21mm and 31mm
respectively (I hesitate to run downstairs again).

Is this the information you're looking for?

No, the pivot to cable measurement is a center-to-center measurement
from the pivot to the closest part of the cable. Imagine a
perpendicular line from the cable where it runs between the "Y" arm and
the "C" arm, to the pivot point. This is the relevant measurement.

Ideally, this should be measured with the brake applied so that the pads
are contacting the rim.

Sheldon "Measurements" Brown
+-------------------------------------------------+
| One measurement is worth 50 expert opinions |
| --Howard Sutherland |
+-------------------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

Quoted message said:

I wrote:

Quoted message said:

Quoted message said:

It's a bad match of lever and caliper; V-brake levers and cantilever
brakes are another example that feels firm but requires unreasonable
hand force to stop.

Your R600 levers are designed for dual-pivot brakes wiuth a high
mechanical advantage (halfway to V brakes) and the Superbe brakes
don't have this.

The illustrious CaptBike said:

That's false.

The R600 levers have essentially the same mechanical advantage as the
Ergos, all "aero" type levers have pretty much the same mechanical
advantage, with the exception of a couple of Dia Compe models.

"Aero" brake levers actually have slightly _higher_ mechanical advantage
than the old-fashioned levers that had the cables exiting the top of the
hood. That's one of the reasons they're superior to the old type.

Far from being a mismatch, installing modern "aero" brake levers is one
of the best ways to upgrade older brake systems.

Quoted message said:

I admit that I have no experience of the Superbe brakes. However, I've
used a 1980s Weinmann single-pivot brakeset which was so weak that (with
maximum hand strength) I couldn't stop the bike rolling away on a 1:4
hill, although people commented on how beautifully firm the brakes
"felt". The calipers were standard reach; the rear pads had to be right
at the bottom of the arms to reach the rim. I tried different pads but
it didn't help the braking.

Those calipers went in the bin a long time ago, but I kept the levers as
spares. When I got my track bike last year I used the RH lever to
operate a front 105 dual-pivot brake. It didn't feel appreciably
different to the same brake worked by a Shimano SLR lever, which I have
on my racing bike, and there was plenty of stopping power. Empirically
at least, the caliper makes a big difference.

Incidentally I've now upgraded to a Dia-Compe 188 lever on the fixed
bike, mainly because I kept catching my elbow on the proudly non-aero
brake cable when getting on and off tri-bars.

Robin Hubert said:

Quoted message said:

On Mon, 28 Feb 2005 01:19:31 GMT, Robin Hubert

[snip]

Quoted message said:

Quoted message said:

Dear Robin,

Can you measure the arms in a few dimensions?

That is, what are the distances from the middle of the brake
pad to the pivot and from the pivot to where the cable
action is applied?

With those, we could work out the actual mechanical
advantage--the difference alone at one point isn't enough.

Long reach pad to pivot: xx mm
Long reach pivot to cable: xx mm

Short reach pad to pivot: xx mm
Short reach pivot to cable: xx mm

The leverage may not be the culprit, but you seem to be
saying that everything is about the same except that one
rear brake is a short reach and the other is a long reach.

Carl Fogel

Hi Carl,

These are measurments from the pads.
74/53mm for the long reach, and 80/49mm for the short reach. I reckon
the pivot to cable (which I take to mean the top of the arm at the bbl
adjuster) can be exrapolated from the above to 21mm and 31mm
respectively (I hesitate to run downstairs again).

Is this the information you're looking for?

Thanks,
Robin Hubert

Dear Robin,

That's getting closer, but not quite what's needed.
Sheldon's reply is a pretty good explanation, and here's an
etch-a-sketch diagram:

cable attaches
C

Sheldon Brown said:

-snip- the pivot to cable measurement is a center-to-center measurement
from the pivot to the closest part of the cable. Imagine a
perpendicular line from the cable where it runs between the "Y" arm and
the "C" arm, to the pivot point. This is the relevant measurement.

Ideally, this should be measured with the brake applied so that the pads
are contacting the rim.

I thought we established that yesterday.
??

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

Robin Hubert said:

Quoted message said:

Hi Carl,

These are measurments from the pads.
74/53mm for the long reach, and 80/49mm for the short reach. I reckon
the pivot to cable (which I take to mean the top of the arm at the bbl
adjuster) can be exrapolated from the above to 21mm and 31mm
respectively (I hesitate to run downstairs again).

Is this the information you're looking for?

Nope.

Carl Fogel replied:

Quoted message said:

Dear Robin,

That's getting closer, but not quite what's needed.
Sheldon's reply is a pretty good explanation, and here's an
etch-a-sketch diagram:

cable attaches
C
.
. brake arm pivot
P .
x .
x .
x |
x |
x |
B | <--brake pad on slotted arm
|
|

The distance from where the cable enters the upper arm C to
the brake arm pivot P is one distance.

No, that is NOT the relevant distance, you want to measure the SHORTEST
distance from the cable to the pivot, W-P in the revised ascii:

Quoted message said:

C
.
. brake arm pivot
W P .
x .
x .
x |
x |
x |
B | <--brake pad on slotted arm
|
|

Quoted message said:

If it's 100 mm from the cable to the pivot

I don't think there are any sidepulls that are that far from cable to pivot

Quoted message said:

and only 50 mm
from the pivot to the brake pad, the ratio of movement is a
feeble 2 to 1.

I took a quick and dirty photo of the 105 single pivot brake on my
Bianchi Brava. Tough with only two hands, so there's some parallax
error, but that one measures about 45 mm.

See: http://sheldonbrown.com/images/cable-distance.jpg

Sheldon "Moment Arm, Not Diagonal Arm" Brown
+-----------------------------------------------------------+
| Oh freddled gruntbuggly |
| thy micturations are to me |
| As plurdled gabbleblotchits on a lurgid bee. |
| Groop I implore thee, my foonting turlingdromes. |
| And hooptiously drangle me with crinkly bind-lewurdles, |
| Or I will rend thee in the gobberwarts with my |
| blurglecruncheon, see if I don't! |
| -- Prostetnic Vogon Jeltz |
+-----------------------------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

On Mon, 28 Feb 2005 19:55:16 -0500, Sheldon Brown
<[email hidden]> wrote:

[snip]

Quoted message said:

Carl Fogel replied:

[snip]

Quoted message said:

Quoted message said:

If it's 100 mm from the cable to the pivot

I don't think there are any sidepulls that are that far from cable to pivot

Quoted message said:

and only 50 mm
from the pivot to the brake pad, the ratio of movement is a
feeble 2 to 1.

[snip]

Dear Sheldon,

I doubt it, too--the figures of 100 mm and 50 mm were chosen
for ease of calculation and as corroborative detail,
intended to give artistic verisimilitude to an otherwise
bald and unconvincing narrative.

Carl Fogel

In article <[email hidden]>, [email hidden]
says...

Quoted message said:

Robin Hubert said:

Quoted message said:

On Mon, 28 Feb 2005 01:19:31 GMT, Robin Hubert

[snip]

Quoted message said:

Quoted message said:

Dear Robin,

Can you measure the arms in a few dimensions?

That is, what are the distances from the middle of the brake
pad to the pivot and from the pivot to where the cable
action is applied?

With those, we could work out the actual mechanical
advantage--the difference alone at one point isn't enough.

Long reach pad to pivot: xx mm
Long reach pivot to cable: xx mm

Short reach pad to pivot: xx mm
Short reach pivot to cable: xx mm

The leverage may not be the culprit, but you seem to be
saying that everything is about the same except that one
rear brake is a short reach and the other is a long reach.

Carl Fogel

Hi Carl,

These are measurments from the pads.
74/53mm for the long reach, and 80/49mm for the short reach. I reckon
the pivot to cable (which I take to mean the top of the arm at the bbl
adjuster) can be exrapolated from the above to 21mm and 31mm
respectively (I hesitate to run downstairs again).

Is this the information you're looking for?

Thanks,
Robin Hubert

Dear Robin,

That's getting closer, but not quite what's needed.
Sheldon's reply is a pretty good explanation, and here's an
etch-a-sketch diagram:

cable attaches
C
.
. brake arm pivot
P .
x .
x .
x |
x |
x |
B | <--brake pad on slotted arm
|
|

On a Shimano 105 I measured C to P as 52mm, P to B as 52mm. Also Cable to P as
44mm per Sheldon. All measurements +/- 1mm.