Brake Cable Routing = Which way is best for performance?

John B. wrote:
On Fri, 21 Feb 2014 16:08:41 +1100, James
wrote:

On 21/02/14 15:32, Joe Riel wrote:
James writes:

On 20/02/14 17:06, Joe Riel wrote:

The modern
brake routing has a smaller total curvature than the old, swoopy, over
the bar routing.


Really? How do you measure that?

ISTM the old had about a 180 degree total curve. Vertical up from the
caliper to vertical down at the lever.

There isn't much different in the front brake, though the modern
routing is shorter, which helps, but probably is not significant.
The routing to the back is definitely better, it eliminates almost
90 degrees of bend.

Really? How do you figure? I get;

180 + 90 + 70 for old

Up from the lever through 180 degrees, then bend toward the back of the
bike with 90 degrees and through another 70 or so to get to the back
caliper.

90 + 90 + 90 + 70 for new

Out from the lever and through 90 degrees around the bend in the bars,
then through 90 degrees to point almost straight down and through
another 90 to point toward the back of the bike, and another 70 to the
caliper as before.

Seems identical!

Additionally I believe you will have to make some allowance for radius
of bend. At least it appears self evident that a large diameter bend,
say from the top of the brake lever to the first cable guide on the
top tube will have less frictional losses then a small radius bend,
say from an aero brake lever around the bend of the handlebar.


Theoretically no, practically only a bit. If the brake cable itself was
perfectly "floppy", it shouldn't matter, as the reduced friction per unit
length should be equally compensated by the increased length over which
that frictional force would act.

On Friday, February 21, 2014 4:13:42 AM UTC-8, John B. wrote:
On Fri, 21 Feb 2014 16:08:41 +1100, James

wrote:



On 21/02/14 15:32, Joe Riel wrote:

James writes:



On 20/02/14 17:06, Joe Riel wrote:



The modern

brake routing has a smaller total curvature than the old, swoopy, over

the bar routing.





Really? How do you measure that?



ISTM the old had about a 180 degree total curve. Vertical up from the

caliper to vertical down at the lever.



There isn't much different in the front brake, though the modern

routing is shorter, which helps, but probably is not significant.

The routing to the back is definitely better, it eliminates almost

90 degrees of bend.



Really? How do you figure? I get;



180 + 90 + 70 for old



Up from the lever through 180 degrees, then bend toward the back of the

bike with 90 degrees and through another 70 or so to get to the back

caliper.



90 + 90 + 90 + 70 for new



Out from the lever and through 90 degrees around the bend in the bars,

then through 90 degrees to point almost straight down and through

another 90 to point toward the back of the bike, and another 70 to the

caliper as before.



Seems identical!



Additionally I believe you will have to make some allowance for radius

of bend. At least it appears self evident that a large diameter bend,

say from the top of the brake lever to the first cable guide on the

top tube will have less frictional losses then a small radius bend,

say from an aero brake lever around the bend of the handlebar.

In either case, friction losses with modern lined cable are probably negligible in a practical sense, regardless of routing. With dual pivot calipers and spring loaded levers, I use less hand strength to break now than I did in the non-aero days, even though the cables are taking fairly hard angles, particularly those that run through the bars.

-- Jay Beattie.

On Friday, February 21, 2014 10:22:43 AM UTC-5, jbeattie wrote:

In either case, friction losses with modern lined cable are probably negligible in a practical sense, regardless of routing. With dual pivot calipers and spring loaded levers, I use less hand strength to break now than I did in the non-aero days, even though the cables are taking fairly hard angles, particularly those that run through the bars.

.... which really makes me wonder why some want hydraulic rim brakes.
http://www.sram.com/news-articles/sr...se-immediately

- Frank Krygowski

James writes:

On 21/02/14 15:32, Joe Riel wrote:
James writes:

On 20/02/14 17:06, Joe Riel wrote:

The modern
brake routing has a smaller total curvature than the old, swoopy, over
the bar routing.


Really? How do you measure that?

ISTM the old had about a 180 degree total curve. Vertical up from the
caliper to vertical down at the lever.

There isn't much different in the front brake, though the modern
routing is shorter, which helps, but probably is not significant.
The routing to the back is definitely better, it eliminates almost
90 degrees of bend.

Really? How do you figure? I get;

180 + 90 + 70 for old

Up from the lever through 180 degrees, then bend toward the back of the
bike with 90 degrees and through another 70 or so to get to the back
caliper.

90 + 90 + 90 + 70 for new

Out from the lever and through 90 degrees around the bend in the bars,
then through 90 degrees to point almost straight down and through
another 90 to point toward the back of the bike, and another 70 to the
caliper as before.

On all three bikes here, the routing from the lever is 90 to make
the first bend, then 90 degrees to the top tube. The transition
from bars to the top tube is angled, so it doesn't require two
90 degree bends, one will do.

--
Joe Riel

John B. writes:

On Fri, 21 Feb 2014 16:08:41 +1100, James
wrote:

On 21/02/14 15:32, Joe Riel wrote:
James writes:

On 20/02/14 17:06, Joe Riel wrote:

The modern
brake routing has a smaller total curvature than the old, swoopy, over
the bar routing.


Really? How do you measure that?

ISTM the old had about a 180 degree total curve. Vertical up from the
caliper to vertical down at the lever.

There isn't much different in the front brake, though the modern
routing is shorter, which helps, but probably is not significant.
The routing to the back is definitely better, it eliminates almost
90 degrees of bend.

Really? How do you figure? I get;

180 + 90 + 70 for old

Up from the lever through 180 degrees, then bend toward the back of the
bike with 90 degrees and through another 70 or so to get to the back
caliper.

90 + 90 + 90 + 70 for new

Out from the lever and through 90 degrees around the bend in the bars,
then through 90 degrees to point almost straight down and through
another 90 to point toward the back of the bike, and another 70 to the
caliper as before.

Seems identical!

Additionally I believe you will have to make some allowance for radius
of bend. At least it appears self evident that a large diameter bend,
say from the top of the brake lever to the first cable guide on the
top tube will have less frictional losses then a small radius bend,
say from an aero brake lever around the bend of the handlebar.

I've measured the losses with significantly different radii and could
detect no change. Admittedly the measurements weren't the most precise,
but seemed adequate. I wrapped brake cable around forms of different
sizes, applying a weight to one end and measuring the force required to
lift it. For really sharp bends there will be an issue. I don't recall
the rule of thumb; probably somewhere around 5-10 cable diameters.

--
Joe Riel

jbeattie writes:

On Friday, February 21, 2014 4:13:42 AM UTC-8, John B. wrote:
On Fri, 21 Feb 2014 16:08:41 +1100, James

wrote:



On 21/02/14 15:32, Joe Riel wrote:

James writes:



On 20/02/14 17:06, Joe Riel wrote:



The modern

brake routing has a smaller total curvature than the old, swoopy, over

the bar routing.





Really? How do you measure that?



ISTM the old had about a 180 degree total curve. Vertical up from the

caliper to vertical down at the lever.



There isn't much different in the front brake, though the modern

routing is shorter, which helps, but probably is not significant.

The routing to the back is definitely better, it eliminates almost

90 degrees of bend.



Really? How do you figure? I get;



180 + 90 + 70 for old



Up from the lever through 180 degrees, then bend toward the back of the

bike with 90 degrees and through another 70 or so to get to the back

caliper.



90 + 90 + 90 + 70 for new



Out from the lever and through 90 degrees around the bend in the bars,

then through 90 degrees to point almost straight down and through

another 90 to point toward the back of the bike, and another 70 to the

caliper as before.



Seems identical!



Additionally I believe you will have to make some allowance for radius

of bend. At least it appears self evident that a large diameter bend,

say from the top of the brake lever to the first cable guide on the

top tube will have less frictional losses then a small radius bend,

say from an aero brake lever around the bend of the handlebar.

In either case, friction losses with modern lined cable are probably negligible in a practical sense, regardless of routing. With dual pivot calipers and spring loaded levers, I use less hand strength to break now than I did in the non-aero days, even though the cables are taking fairly hard angles, particularly those that run through the bars.

-- Jay Beattie.

I wouldn't say they are negligible. Mountain bike levers have reduced
cable losses because they eliminate more than 90 degrees of bend in the
cable routing; I suspect it's one of the reasons they usually feel
better.

--
Joe Riel

On Friday, February 21, 2014 10:46:41 AM UTC-5, JoeRiel wrote:

I've measured the losses with significantly different radii and could
detect no change. Admittedly the measurements weren't the most precise,
but seemed adequate. I wrapped brake cable around forms of different
sizes, applying a weight to one end and measuring the force required to
lift it. For really sharp bends there will be an issue. I don't recall
the rule of thumb; probably somewhere around 5-10 cable diameters.

IIRC, the theoretical formula is T1/T2 = e^(f*theta). The T terms are high side and low side tensions. f is friction coefficient and e is the base of natural logs. The equation contains no radius term.

In some cases, simple theoretical equations need modification to properly predict real-world behavior, but I don't think this is one of them, at least for any reasonable radius.

- Frank Krygowski

On Fri, 21 Feb 2014 13:46:54 GMT, Ralph Barone
wrote:

John B. wrote:
On Fri, 21 Feb 2014 16:08:41 +1100, James
wrote:

On 21/02/14 15:32, Joe Riel wrote:
James writes:

On 20/02/14 17:06, Joe Riel wrote:

The modern
brake routing has a smaller total curvature than the old, swoopy, over
the bar routing.


Really? How do you measure that?

ISTM the old had about a 180 degree total curve. Vertical up from the
caliper to vertical down at the lever.

There isn't much different in the front brake, though the modern
routing is shorter, which helps, but probably is not significant.
The routing to the back is definitely better, it eliminates almost
90 degrees of bend.

Really? How do you figure? I get;

180 + 90 + 70 for old

Up from the lever through 180 degrees, then bend toward the back of the
bike with 90 degrees and through another 70 or so to get to the back
caliper.

90 + 90 + 90 + 70 for new

Out from the lever and through 90 degrees around the bend in the bars,
then through 90 degrees to point almost straight down and through
another 90 to point toward the back of the bike, and another 70 to the
caliper as before.

Seems identical!

Additionally I believe you will have to make some allowance for radius
of bend. At least it appears self evident that a large diameter bend,
say from the top of the brake lever to the first cable guide on the
top tube will have less frictional losses then a small radius bend,
say from an aero brake lever around the bend of the handlebar.


Theoretically no, practically only a bit. If the brake cable itself was
perfectly "floppy", it shouldn't matter, as the reduced friction per unit
length should be equally compensated by the increased length over which
that frictional force would act.

I'm not too sure how effective "theoretically" is. If you were to
coil your brake cable in a loop with, say an inner diameter of 1/4
inch would the friction losses be the same as for the cable coiled in
a 2 foot circle?
--
Cheers,

John B.

On Fri, 21 Feb 2014 07:26:30 -0800 (PST), Frank Krygowski
wrote:

On Friday, February 21, 2014 10:22:43 AM UTC-5, jbeattie wrote:

In either case, friction losses with modern lined cable are probably negligible in a practical sense, regardless of routing. With dual pivot calipers and spring loaded levers, I use less hand strength to break now than I did in the non-aero days, even though the cables are taking fairly hard angles, particularly those that run through the bars.

... which really makes me wonder why some want hydraulic rim brakes.
http://www.sram.com/news-articles/sr...se-immediately

- Frank Krygowski

It is "progress"; being "modern"; they are "wonderful". Or to quote a
best selling English author, "Oh-My-God..... that-is-sooo-cool".

If you don't watch out Frank, the next thing you'll be decrying
plastic bicycles :-)
--
Cheers,

John B.

routing

http://goo.gl/PZgd4e