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Old 05-25-2013, 05:17 PM   #16
robtg
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It's all about modulating the brake, hard to do accuratley while blowing up the rubber lines like balloons.
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Old 05-25-2013, 05:36 PM   #17
supershaft
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Originally Posted by robtg View Post
it's all about modulating the brake, hard to do accuratley while blowing up the rubber lines like balloons.
+1
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Old 05-26-2013, 01:45 PM   #18
190e
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Originally Posted by Plaka View Post
and when the rubber lines expand under pressure...um...then what happens? Is there less pressure?
If a rubber line expanded, pressure would be the same but feel would change due to more lever movement.

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Originally Posted by Plaka View Post
Have you ever tried measuring that expansion...like with a micrometer? You know, just put it on the outside of the line, squeeze hard and check the diameter.
I've done it recently with digital calipers and detected no expansion. Maybe not as accurate as a micrometer but sensitivity is half a thou and any expansion readily observed. I saw none, even when squeezing the lever hard as I could. Only measured at one point along the length of the hose so perhaps not a definitive test.
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Old 05-26-2013, 02:46 PM   #19
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Originally Posted by photomd View Post
I had mine made at a local hydrolic line shop. It was about $30 for the only hose on my Airhead. Both my other bikes have lines I made from these Magnum Kits from MG Cycle: Very easy kit to use.
I was going to suggest the very same thing, but saw that you had beat me to it. I just used these on my 850T3, and was beyond happy with the whole thing. It is really nice to be able to make the line exactly the length you want, and figure it out while you do it. The price is low too.
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Old 05-26-2013, 02:59 PM   #20
supershaft
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Quote:
Originally Posted by 190e View Post
If a rubber line expanded, pressure would be the same but feel would change due to more lever movement.



I've done it recently with digital calipers and detected no expansion. Maybe not as accurate as a micrometer but sensitivity is half a thou and any expansion readily observed. I saw none, even when squeezing the lever hard as I could. Only measured at one point along the length of the hose so perhaps not a definitive test.
The brake lever only moves so far. If the brake line swells, that energy is expanding the brake line and not moving the caliper piston. You can't have both things happening at once. It's one or the other at every increment of the brake lever. As far as the brake lever movement is concerned, you have the piston moving more if the line swells less all the way down until the lever bottoms out on the throttle grip. If that isn't better brakes I don't know what is. How much do the rubber lines swell? I never felt the need to measure it since I can feel it without a doubt and then some through the lever. I don't care how much the lines swell. The difference felt through the lever is night and day. That's all the proof I need.
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Old 05-26-2013, 03:45 PM   #21
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Originally Posted by 190e View Post
If a rubber line expanded, pressure would be the same but feel would change due to more lever movement.



I've done it recently with digital calipers and detected no expansion. Maybe not as accurate as a micrometer but sensitivity is half a thou and any expansion readily observed. I saw none, even when squeezing the lever hard as I could. Only measured at one point along the length of the hose so perhaps not a definitive test.
If pressure is the same then braking force is the same.

I blew a line recently and I have an old factory line patched onto my MC to test it. I'll check for expansion with a Digimic. and then cut it open and peek inside. I got a feeling there is a pretty hard line under that rubber.


Think we've been taken for a ride all these years? Or maybe other lines expand, not the superior BMW ones?

I know a little bit about sensory psychology somehow. Look up "expectation matrix" (if memory serves). it's the thing that creates certain sensory illusions---like when you are sitting at a light in the car and the car next to you rolls forward and you think it is yourself rolling backward---and brake hard!.
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Old 05-26-2013, 04:47 PM   #22
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Measured expansion about .025" (rounded) under very heavy two handed pressure. This is an old stock line, MC to splitter, deadheaded at the splitter. Haven't gotten to cutting it open, rushed on other projects at the moment. May not. It does expand.



Note: pic is my neighbor modeling. For the measurements he did the squeezing and I measured the line, at several points avoiding the rub tubing.
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Old 05-26-2013, 05:42 PM   #23
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^Thanks for doing the research, very interesting. That said, I didn't need any numbers to know that braided lines work better. There is no comparison in feel.
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Old 05-26-2013, 06:21 PM   #24
supershaft
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^Thanks for doing the research, very interesting. That said, I didn't need any numbers to know that braided lines work better. There is no comparison in feel.
Exactly. You can experience reality or you can read snobum. The two are very often at odds and this is one of those times.

If pressure is the same then braking in the same. That statement is forgetting the brake lever. At any point in the brake lever's travel, if the brake line has not swelled, there is more pressure and better braking than if it has swelled. It is as simple as that.

Better braking is better braking. No one that has actually used steel braided lines has been fooled for all these years. People reading snobum? And believing all of it? That's were being fooled comes into play.
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Old 05-26-2013, 06:26 PM   #25
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it's all about modulating the brake, hard to do accuratley while blowing up the rubber lines like balloons.

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Old 05-26-2013, 06:35 PM   #26
supershaft
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+1 . . . again.
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Old 05-26-2013, 06:54 PM   #27
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I made the switch from OEM to SS braided and yes, the "feel" is noticeably harder with the SS. With the adrenaline pump of a near collision, I've locked both the front disk and rear drum on my 38 year old /6. There's no doubt in my own mind that when it comes to emergency braking, it's more about the adrenaline than it is about the rubber v. SS front brake line. That's a long winded way of saying I think either one gets the job done.
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Old 05-26-2013, 08:15 PM   #28
batoutoflahonda
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In reply to sourcing. I went down to my local hose shop and for 40 bucks I was out the door in less time than it took to pay for it. Take the line with you.
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Old 05-27-2013, 01:46 AM   #29
190e
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I don't think anyone is arguing that new braided lines can give a firmer feel or that old rubber lines can swell under pressure but in the majority of cases it's an old vs new senario so the improvement is no surprise and would have been achieved at least to some extent with new rubber lines. I've just nipped out to the garage again and tested my rubber lines. Still can't measure even half a thou change using one handed firm pressure on the lever. There must be something different about the lines when Plaka is measuring 25 thou and I can't measure half a thou. Maybe I need stronger hands as they are many times older than the rubber.

I'm not daft enough to suggest that rubber lines are the thing to have but I do want to dispel the myth that all rubber lines blow up like a balloon under typical working pressure. That has to be nonsense or BMW wouldn't have fitted them in the first place.

Here's a link to a comparative test on rubber vs braided which appears to show that old rubber lines do swell more than new rubber. Braided is better still. Mind they admit to using over double the pressure that would be experienced while braking and that might be many times the pressure I'm exerting. Anyone know what pressure our systems achieve in practice ?

http://www.autospeed.com/cms/article...e-Lines&A=2679

190e screwed with this post 05-27-2013 at 01:54 AM
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Old 05-27-2013, 08:29 AM   #30
Plaka
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Originally Posted by 190e View Post
I don't think anyone is arguing that new braided lines can give a firmer feel or that old rubber lines can swell under pressure but in the majority of cases it's an old vs new senario so the improvement is no surprise and would have been achieved at least to some extent with new rubber lines. I've just nipped out to the garage again and tested my rubber lines. Still can't measure even half a thou change using one handed firm pressure on the lever. There must be something different about the lines when Plaka is measuring 25 thou and I can't measure half a thou. Maybe I need stronger hands as they are many times older than the rubber.

I'm not daft enough to suggest that rubber lines are the thing to have but I do want to dispel the myth that all rubber lines blow up like a balloon under typical working pressure. That has to be nonsense or BMW wouldn't have fitted them in the first place.

Here's a link to a comparative test on rubber vs braided which appears to show that old rubber lines do swell more than new rubber. Braided is better still. Mind they admit to using over double the pressure that would be experienced while braking and that might be many times the pressure I'm exerting. Anyone know what pressure our systems achieve in practice ?

http://www.autospeed.com/cms/article...e-Lines&A=2679
I was looking for worst case so I had Dusting crunch the lever with both hands. And then I'm using a digital micrometer, not a caliper, which is reading to .0001". Then I rounded up sort of to simulate the lines on a hot day in the sun.

However, a "hard" feel is not necessarily a better feel. It depends on what one prefers. The softer feel can be more sensitive. People think if the lever feels real hard the braking must be better. Nope . Even if there is some air in the system giving a soft lever, pressure is pressure is pressure. That is the only thing that matters for a given setup. (that is, given pads and rotor, etc.)

However there are a bunch of ergonomic factors. The hand has the most strength with the wrist strait. So rotating the entire brake assembly on the bar to put the plane the lever travels in in line with the arm is good. Also the fingers have the most strength at mid extension. here the harder feel helps because there is less lever travel and the levers can be set closer to the bar if you have a smaller hand. This may require an adjustable or modified lever. The size of the handgrip used also figures.

All of this of course is about getting better braking from the marginal (in modern terms) systems on the older airheads. My K100RS had two finger front brakes, all I could want, and that was a heavy, fast bike.

I have no idea what the system pressure is. The trick to computing it is to find the force on the MC piston. That in turn is a function of the force applied to the lever working through the leverage of the lever pivot. The force applied to the MC piston times the surface area of the end of the piston (Pi x MC bore, squared) is the operating pressure. You could measure at the caliper end if you can find the force the pads are exerting. Same formula using the caliper piston diameter.
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