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#31
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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. |
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#32
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Brake Cable Routing = Which way is best for performance?
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. |
#33
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Brake Cable Routing = Which way is best for performance?
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 |
#34
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Brake Cable Routing = Which way is best for performance?
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 |
#35
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Brake Cable Routing = Which way is best for performance?
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 |
#36
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Brake Cable Routing = Which way is best for performance?
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 |
#37
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Brake Cable Routing = Which way is best for performance?
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 |
#38
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Brake Cable Routing = Which way is best for performance?
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. |
#39
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Brake Cable Routing = Which way is best for performance?
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. |
#40
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Brake Cable Routing = Which way is best for performance?
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