Brake lines - twin lines or h ?

[Gix]

When getting new braided lines, I have always gone for the twin, separate lines option as in my mind and it has always been told to me that twin lines was the optimum set up.

I see more and more race or track bikes with aftermarket braided hoses with the 'h' set up, in fact, it seems to be the norm. Am I missing something or am I stuck in the nineties?

Which is best and why?

[Damnthistinleg]

1 minute ago, Gix said:

When getting new braided lines, I have always gone for the twin, separate lines option as in my mind and it has always been told to me that twin lines was the optimum set up.

I see more and more race or track bikes with aftermarket braided hoses with the 'h' set up, in fact, it seems to be the norm. Am I missing something or am I stuck in the nineties?

Which is best and why?

Twin lines every time for me but a splitter on the bottom yoke is okay at a pinch.

Incidentally, I thought the 'h' setup was a scrutineering fail on a race bike. It certainly used to be.

 

[jaycee]

8 minutes ago, Damnthistinleg said:

 

Incidentally, I thought the 'h' setup was a scrutineering fail on a race bike. It certainly used to be.

 

What is the reason for this? I was told that if one line fails, the second line is still there, but that would only work if there was some sort of rupture valve to keep pressure in the system.

Edited June 13 by jaycee

[Damnthistinleg]

7 minutes ago, jaycee said:

What is the reason for this? I was told that if one line fails, the second line is still there, but that would only work if there was some sort of rupture valve to keep pressure in the system.

It's more about the possibility of the hoop getting caught up with the tyre if the mudguard breaks.

That's how I remember it, anyways.

[hawkati]

1 hour ago, Damnthistinleg said:

It's more about the possibility of the hoop getting caught up with the tyre if the mudguard breaks.

That's how I remember it, anyways.

Very much this - I remember a bike crashing at Oulton Park for this reason. They'd used plastic numberplate bolts on the mudguard ffs...

Separate twin hoses for me, for this reason. 

[nampus]

I would always go twin lines or decent splitter at the bottom yoke. 

The single line to a caliper then loop to the opposite caliper just looks shit. 

And for reasons mentioned previously of course. 

Twin lines might be easier to bleed, the hoop over the wheel looks like a great place for an air bubble. 

Edited June 14 by nampus

[David W]

Last few bikes I’ve done I went with a line to caliper and then a line over the mudguard. I get that it’s banned in racing in case a mudguard comes off and then the brake line decides to throw itself into a wheel bit I made the grownup calculation that statistically there’s a thousand things will probably kill me before that happens. Meteorite strike and being targeted by a rogue Reaper Drone probably higher on the list 😂

Main reason for doing it that way is it makes the packaging at the handlebar much neater especially because I was using Brembo master cylinders and pressure banjo switches.

[2moto]

Splitter at bottom yoke on everything I've done. Passes race regs and convenient to route. Having two banjos at the master is often too bulky. I use Venhill powerhose stuff exclusively. 

[David W]

8 hours ago, jaycee said:

What is the reason for this? I was told that if one line fails, the second line is still there,

You’d be surprised how many people still regurgitate that nonsense.

[426hemi]

I’ve always run twin lines but I had pcr make me h lines for the pb blade as the ones on it were slightly long and didn’t sit neatly.

[dab33]

H set up on both of mine, so long as it use the bottom yoke to cross between the fork legs all good for technical inspection. 

It's more expensive to buy, but a nice tidy installation when it's done well.

Edited June 14 by dab33

[2639]

The h pattern was outlawed on the grounds of safety. However it was nothing to do with mudguards. People continually failed to allow for outward travel of an unloaded fork at installation. Thus hard acceleration was introducing spring pressure and wheel travel inertia against the brake line joints and unions. Which caused a pattern of failures.

I suppose now, when few people make thier own lines things might be different. Way back when we were all skint, the cheapest way into braided kines was Goodrich build a line and a roll of braided you cut to suit. And if you was really posh... new olives!

Dictating the split has to be above the lower edge of the bottom yoke is only really because its clear to communicate to the hard of thinking.

In the.age of modern easy datalogging... if anyones bored.... pressure transducers on either banjo bolt please. Pressure should be uniform accross the system, but always wondered if the real world introduced delays or variance somehow. Maybe real time infrared cameras tracing heat of the pads???

Yours sincerely

Someone who needs to get out more.

[Superdunc]

There is no pressure variance in the system.

The set up out lawed for racing is the loop between caliper over the mudguard as per most standard road bikes.  Suspension travel has no effect on the loop. 

[David W]

The whole concept of hydraulics is pressure is the same everywhere. OK there might be a microsecond difference as the pressure spreads through the system or rubber hoses swelling a tiny bit but that’s it.

Making lines that are shorter than your fully extended suspension just proves you can’t legislate against idiocy 😂

[jaycee]

55 minutes ago, Superdunc said:

There is no pressure variance in the system.

 

 

31 minutes ago, David W said:

The whole concept of hydraulics is pressure is the same everywhere.  

Thank you!

[2639]

I know pressure is uniform accross the system. In the classroom at least. Justvthat several things taught in a classroom are 'starters' to ensure a student grasps the fundamental. Whole weighty textbooks await the interested and determined.

I merely speculate it might not be as black and white as that in a real application. I can feel the difference in bore size of a brake line. I can feel some give in rubber brake lines, and actually quite like the sensation and the, possibly percieved ease of brake modulation. I strongly suspect I have ben able to recognise a difference in brake fluid brand when back to back riding. Im aware there is likely disbelief at that, but I dont write fantasy here or anywhere else.

I dont think we should dismiss small or detail changes on a time basis. If I break down the number of operations I make when riding and the difference between a good lap and a bad. Were looking at vatriance well under tenths per operation for everything. Hundredths, definately. So why not milliseconds? 

Finally us humans are funny creatures. Ive said the reason for the ruling was incorrectly installed lines pulling taught lead to a pattern of brake failure. Two posts later Dunc says suspension travel has no effect on the loop. This isnt a dig Dunc. Its an observation on our collective language and communication. We both have significant experience, perhaps so much to forget the apprentice errors.

But it remains that something as simple as not having fouled brake lines has resulted in mandatory ruling (for the environment where owner maintenance and self made parts are commonplace, racing).

And would anyone else, understanding how rules books are almost always reactive, wonder what happened. You'd suspect theres a dozen or so, big scares/ heavily injured/dead incidents. The first couple will have been 'a one of them', news wouldnt have travelled so far. Possibly, eventually, the fatal happened proximate to a technically aware, conscientious communicative man and a slow chain of event rumbled to fruition. It'll have taken some time though. 

But a few decades later, the real reason remains clouded in hearsay and we still cant write an unambiguous posts on the subject.

Anyway.... more fixing and less internet.

[Gobert]

@ZXRRDave I thought the "h" line set up was ok as long as the crossing line was above a certain point as per @dab33 's post?

[dab33]

1 hour ago, Gobert said:

@ZXRRDave I thought the "h" line set up was ok as long as the crossing line was above a certain point as per @dab33 's post?

My CBR has past technical inspection twice this year with NL endurance, and @ZXRRDavedid the inspection at round 1.

[Gobert]

Just now, dab33 said:

My CBR has past technical inspection twice this year with NL endurance, and @ZXRRDavedid the inspection at round 1.

so there we go....

[Superdunc]

8 hours ago, 2639 said:

I know pressure is uniform accross the system. In the classroom at least. Justvthat several things taught in a classroom are 'starters' to ensure a student grasps the fundamental. Whole weighty textbooks await the interested and determined.

I merely speculate it might not be as black and white as that in a real application. I can feel the difference in bore size of a brake line. I can feel some give in rubber brake lines, and actually quite like the sensation and the, possibly percieved ease of brake modulation. I strongly suspect I have ben able to recognise a difference in brake fluid brand when back to back riding. Im aware there is likely disbelief at that, but I dont write fantasy here or anywhere else.

I dont think we should dismiss small or detail changes on a time basis. If I break down the number of operations I make when riding and the difference between a good lap and a bad. Were looking at vatriance well under tenths per operation for everything. Hundredths, definately. So why not milliseconds? 

Finally us humans are funny creatures. Ive said the reason for the ruling was incorrectly installed lines pulling taught lead to a pattern of brake failure. Two posts later Dunc says suspension travel has no effect on the loop. This isnt a dig Dunc. Its an observation on our collective language and communication. We both have significant experience, perhaps so much to forget the apprentice errors.

But it remains that something as simple as not having fouled brake lines has resulted in mandatory ruling (for the environment where owner maintenance and self made parts are commonplace, racing).

And would anyone else, understanding how rules books are almost always reactive, wonder what happened. You'd suspect theres a dozen or so, big scares/ heavily injured/dead incidents. The first couple will have been 'a one of them', news wouldnt have travelled so far. Possibly, eventually, the fatal happened proximate to a technically aware, conscientious communicative man and a slow chain of event rumbled to fruition. It'll have taken some time though. 

But a few decades later, the real reason remains clouded in hearsay and we still cant write an unambiguous posts on the subject.

Anyway.... more fixing and less internet.

I like to stick to first principles, there is no variance in pressure in a barke system.

The observations about feel are relavent. Smaller bore braided lines are generally stiffer and gave less hysteresis, so give a more positive feel at the lever, and more of the energy applued at the lever is converted into braking pressure. F1 and top end sports cars have just a few centimeters of flexible hose in the whole brake system, literally the bare minimum so they get the maximun feel and efficiency.

On a bike this isnt as critical as we have effort to spare with the grip avalable, but feel is even more critclal.

I suspect its the fact that the 'h' line set-up uses less overall house length so less flex in the lines, and you get a more consistent feel, is what has made it the more usual choice these days.

[ZXRRDave]

H section line is the norm in the bsb paddock, the preference is for a single banjo at the master cylinder as apparently they are less prone to damage when knocked and ess prone to damaging the master cylinder in turn.

No join in the line or crosspiece of hose may sit under the bottom edge of the lower yoke, when I needed to leverage the BMW's regs (as bmw and the series organiser were keen to use the standard item that uses a junction join bolted under the yoke) Stuart Higgs and Paul King both referred to the death of a rider at a Brands wsb round who had hit a lost kneeslider at surtees that ripped his mudguard off and severed the brake lines at the join below the yoke. This resulted in him reaching Hawthorns with no brakes, which caused the fatality. 

No join below the yokes is the reg, single line from the master cylinder is the team's ideal solution. It also makes plumbing in a pressure sensor easier, as they run a line down to a T piece, then a line down to the caliper and across to the other fork leg, where a second t piece goes down to the caliper and has a pressure sensor attached to the top.

[Superdunc]

5 minutes ago, ZXRRDave said:

H section line is the norm in the bsb paddock, the preference is for a single banjo at the master cylinder as apparently they are less prone to damage when knocked and ess prone to damaging the master cylinder in turn.

No join in the line or crosspiece of hose may sit under the bottom edge of the lower yoke, when I needed to leverage the BMW's regs (as bmw and the series organiser were keen to use the standard item that uses a junction join bolted under the yoke) Stuart Higgs and Paul King both referred to the death of a rider at a Brands wsb round who had hit a lost kneeslider at surtees that ripped his mudguard off and severed the brake lines at the join below the yoke. This resulted in him reaching Hawthorns with no brakes, which caused the fatality. 

No join below the yokes is the reg, single line from the master cylinder is the team's ideal solution. It also makes plumbing in a pressure sensor easier, as they run a line down to a T piece, then a line down to the caliper and across to the other fork leg, where a second t piece goes down to the caliper and has a pressure sensor attached to the top.

Do the run a bleed nipple on the brake pressure sensor?

[ZXRRDave]

5 minutes ago, Superdunc said:

Do the run a bleed nipple on the brake pressure sensor?

Not that I've seen, I think they use a fairly strong vacuum bleeding rig though.