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How Brake System Plumbing Affects Brake "Feel"

How Brake System Plumbing Affects Brake "Feel"

How Brake System Plumbing Affects Brake "Feel"

(OP)
Hi all,

First post. My question is regarding an attempt to discover why changes to brake system plumbing change the way the brakes "feel" to the vehicle operator.

More specifically, I'm concerned only about changes to the flexible hoses in terms of material and/or internal diameter. An example could be replacing rubber brake hoses with hoses made from stainless steel braided PTFE, but I would also like to explore replacing larger diameter braided stainless hoses with smaller inside diameter hoses.

My core question is, "Why exactly do these changes change the feel of a brake system?"

Would you agree that the change from rubber to braided stainless changes system feel because of the reduction in hose expansion? That alone?

Then regarding the change from larger ID braided stainless hoses to smaller, is the change in system feel in that case also due to a reduction in expansion? Some other aspect, such as the reduction in fluid volume, or the smaller fluid pathway?

If all of these effects have an impact on system feel, is there a rank order to them in terms of their impact?

I'd further like to discuss whether, given a fixed plumbing spec, can feel be changed via restriction of fluid flow through addition of an orifice of some kind.

Thanks!

Chris

RE: How Brake System Plumbing Affects Brake "Feel"

The "rule of thumb" in racing has been to use the smaller dia braided SS AN/PTFE hoses for flexible connections.  It is so ingrained in our modern race culture as to be thought of as a "given"!
Now, since I have spent almost all of my adult life building and racing various cars and bikes...I will disagree with most of what is posted on the race car sites.  What brake hoses/pipes are best for any single application, vis a vis "feel" will vary ... A LOT.
For some vintage iron, the OEM type hoses often suffice and no advantage can be felt with AN hardware...For modern cars, the "feel" with AN hoses over OEM is pretty subjective.  Not much change from my point of view.

The real reason I choose braided hose over OEM is more availability/cost and, I have the ability to fab any application as needed---No parts chasing.  Maintenance and longevity are much the same, but cost of custom "rubber" piping can be enormous.  I only choose to use it where authenticity is paramount, such as my 23 T tub 50's era track roadster (OEM style front hoses ~$79).

Bottom line...Purely racing applications...Braided SS
High performance street...Either braided SS or performance grade OEM pieces.  Any "change" in feel is usually attributable to replacing "old" parts with "new" and not from "rubber" to "braided".

Feel is subjective.  If that's your primary concern you may or may not see a change.  If you want it to "look" racery, go for the shiny stuff.

Rod

RE: How Brake System Plumbing Affects Brake "Feel"

(OP)
Thanks Rod,

Would you agree that the ideal design for brake plumbing would be 100% solid tubing, but since we need to accommodate suspension travel and steering movement, the next best thing is a hose with as little expansion as possible?

Regarding old to new vs rubber to braided, what if both were new (rubber and braided)? If there then was a change in feel, would it be attributed to the change in expansion spec or something else? Then what if you swapped the still new stainless hoses out with stainless of a smaller ID and had a change in feel again? Would it be attributed to the reduction in expansion? The smaller ID allowing less volume of fluid in the system? The smaller channel for the fluid to move through?

And finally, all other things remaining equal, would there be any merit to having the ability to insert and change the size of a fluid "restrictor" inline in the brake system, in terms of adapting feel to preference?

Thanks,

Chris

RE: How Brake System Plumbing Affects Brake "Feel"

what would be the goal of the restrictor?  to make it hard to get the pedal down quickly, but give the same force once the pedal is down?

RE: How Brake System Plumbing Affects Brake "Feel"

(OP)
The restrictor would be used to modify the feel of the pedal. I wouldn't want to say make it hard to move the pedal, but rather to change the way the pedal feels via changing the size of the restriction.

Chris

RE: How Brake System Plumbing Affects Brake "Feel"

A restrictor small enough to be effective would be dangerous in a brake system.

My Camaro's hydraulic clutch has a restrictor to limit the drivetrain shock damage you can cause by sidestepping the pedal, but that's a different application.

 

Mike Halloran
Pembroke Pines, FL, USA

RE: How Brake System Plumbing Affects Brake "Feel"

You can build a very simple model of the hydraulic circuit, and you need to know the stiffness of your calliper/pad setup and then you can use it to create a budget of compliance in the system.
 

Cheers

Greg Locock

I rarely exceed 1.79 x 10^12 furlongs per fortnight

RE: How Brake System Plumbing Affects Brake "Feel"

(OP)
So, to parse out a portion of one of my above posts:

Is the ideal design for brake plumbing 100% solid tubing?

Since we need to accommodate suspension travel and steering movement, the next best thing is using hose with as little expansion as possible?

Once we have that in place, have we done all we can do as far as optimizing the plumbing or is adding a restrictor to the mix a value-add prospect?

Chris

RE: How Brake System Plumbing Affects Brake "Feel"

Do not add a restrictor.

Cheers

Greg Locock

I rarely exceed 1.79 x 10^12 furlongs per fortnight

RE: How Brake System Plumbing Affects Brake "Feel"

(OP)
Fair enough.

Do you think, then, that any change in the feel of a brake system caused by a change to the flexible hoses is specifically and only because of differences in the expansion characteristics of those hoses?

Chris

RE: How Brake System Plumbing Affects Brake "Feel"

(OP)
What if it's just a fractional restrictor? Say the lines have an ID of 3.2mm and the restrictor has an ID of 3.0mm?

Chris

RE: How Brake System Plumbing Affects Brake "Feel"

(OP)
Sorry to keep bringing the restrictor up. Just exploring an idea...

Chris

RE: How Brake System Plumbing Affects Brake "Feel"

Chris, forget the restrictor idea, period!

All steel is probably the best as far as line expansion goes. I doubt that such a system could be made viable.  Even if it could, I seriously doubt you could tell the difference in everyday use.

Let's get another idea out of the way while we are at it.  The modern OEM brake hoses and piping do not "expand" any more or less than the AN -03 PTFE stuff that I use...At least to any degree that you can feel under you foot. OEM lines are still "braided" material simply coated with a "rubber" outer for resistance to weather---Something that AN braided SS is not ANY better at than OEM.  In racing, the brakes are attended too after each race.  Treat OEM stuff the same way and they will be just as effective as AN hardware.  Like I said, safety, expansion, wear resistance/longevity are NOT why I use AN hardware---Cost, availability and, custom applications are!

No OEM puts substandard braking systems on new cars, at least none that I know of.  It would be suicide.

Rod

 

RE: How Brake System Plumbing Affects Brake "Feel"

(OP)
The application I'm focused on is motorcycles. My gut guess would be that the type of hose makes more difference on a motorcycle because it composes the bulk of if not 100% of the plumbing. Contrast that to a car, where the flexible portion of plumbing is a small percentage.

That said, you can put a bike with OE rubber lines next to a bike with SS lines and feel a distinct difference at the lever between the two.

My effort here was to try to get to the bottom of what about the lines creates that difference in feel. If not expansion, what?

The specs I have for SS hose shows an "elongation" allowance of +2%. I'm going to quasi-equate that to expansion specs.

Does anyone have comparable specs for OE rubber lines, or comparison specs? Maybe I should visit the Eaton website...

Chris

RE: How Brake System Plumbing Affects Brake "Feel"

Isn't "feel" a kinda subjective criteria?

RE: How Brake System Plumbing Affects Brake "Feel"

well, it'll sure change the "feel" if you stop the fluid getting to the calipers and/or back out... they'll start to feel less like functional brakes.

RE: How Brake System Plumbing Affects Brake "Feel"

It is really VERY straightforward, to the point that a detailed explanation is really quite insulting to a real engineer.

The restriction only limits fluid flow rate vs pedal force. Restricting flow makes the pedal feel heavy or slow to apply the brakes.

Once the pad hits the disc and starts to clamp the restriction will have no influence as the pressure equalises in the system.

The clamping process after contact has much less travel than take up of clearance, so the restriction has little influence as it only impacts on flow rate, not pressure at equilibrium.

Off the top of my head, the things that effect feel once a pad is being clamped are:-
Compliance in the lines.
Compliance in the callipers.
Compressibility of the fluid.
Co-efficient of friction between the pad and the rotor.
Compliance of the rotor surface.
Projected area of the master cylinders piston.
Projected area of the calliper piston or pistons.
Compliance in the pedal assembly.
Effects of changes in temperature of various components.

Note

As far as I know, rubber brake lines are steel braided. It is just that the braid is not stainless and it is covered by rubber both inside and out.

Solid steel lines are much more rigid than flexible lines.




 

Regards
Pat
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RE: How Brake System Plumbing Affects Brake "Feel"

(OP)
Thank you.

RE: How Brake System Plumbing Affects Brake "Feel"

On most newer motorcycles, replacing the brake lines with braided steel makes scant if any difference to brake lever feel on its own. BUT.

If you want to change the location of the handlebars for roadracing or whatever, or change the master cylinder or calipers to ones that have different orientation of the end connections, often you can't use the original-equipment lines, and as others noted, it's a whole lot easier (and generally less expensive) to make something up with braided steel to suit than it is to chase around looking for some other OEM brake line that will coincidentally fit what you have done.

The other thing is that quite a number of late model Suzuki and Kawasaki motorcycles have a brake line routing in which a single brake line goes down to one caliper, then there is a double banjo fitting at that caliper and a cross-over hose to the other side. This causes a situation where the cross-over hose has a high spot, and if any air gets into the brake system (or if you have to service the brakes during a race weekend) it's really hard to bleed that air bubble out quickly using the equipment available at the racetrack. If you change it to the normal arrangement (two separate hoses to each side from the master cylinder) then bleeding the brakes in the field is a lot easier - but can't do that with the original-equipment hoses. The OEM doesn't care about this, because they can just pull a complete vacuum on the system (not just "suction" like a brake bleeding kit uses - I mean a complete vacuum so that there is no air left), but you can't do that with what's available in hot pit lane ...  

RE: How Brake System Plumbing Affects Brake "Feel"

Okay, I'll still say that feel is subjective.  I owned a 1977 KZ 650 Custom.  Rode it to Mexico City and back.  It had dual front disc brakes with two "rubber" hoses that ran from a "t" near the triple tree. Quite long, considering.  At around 30,000 miles I rebuilt the brakes and changed the hoses to AN -03 braided SS for many if not most of the reasons you seem bent on accomplishing.  Again, in retrospect, I don't recall any great changes in "feel", aside the obvious that I WANTED AND EXPECTED to "feel" BETTER !!!
Looking back, that little bike always had superior brakes, before AND after I fooled around with them.  It was the first bike I owned with fully hydraulic disk brakes.  I finally sold it at 39,000 still with the ORIGINAL 'O' ring chain !!!(Gettin' older, traded for an '80 Goldwing)

Hard to grasp "feel" if you are too closely involved in the changes.

Rod

RE: How Brake System Plumbing Affects Brake "Feel"

A real test of feel is to see if someone unaware which way the changes were made consistently notices a change in feel that matches changes vs no change.

Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
http://eng-tips.com/market.cfm
for site rules
 

RE: How Brake System Plumbing Affects Brake "Feel"

I suspect (with no physical evidence) that braided hoses are expected to work better and so are fitted to all braking systems that are already better.  I would be suprised to see an expensive 6-pot calliper with anything else attached to it.  Likewise, my old GPz and its twin-pots only had good old rubber.

I wonder if metallic blue banjo fittings give a better feel too?  Or (on cars) callipers painted red?
 

- Steve

RE: How Brake System Plumbing Affects Brake "Feel"

I was under the impression that the braid is a fairly loose sleeve over the rubber. A such it seems unlikely that braid is the difference between a radially stiff hose and a compliant one.

 

Cheers

Greg Locock

I rarely exceed 1.79 x 10^12 furlongs per fortnight

RE: How Brake System Plumbing Affects Brake "Feel"

SG,

Hey now!  My calipers are painted red... of course, I think that was my attempt to hide the rust, but that's another story!

Dan - Owner
http://www.Hi-TecDesigns.com

RE: How Brake System Plumbing Affects Brake "Feel"

I have a coworker who spent an entire week of vacation carefully painting the calipers on his BMW.  It was made more difficult, I imagine, by his unwillingness to unbolt anything other than the wheels (for fear what might happen).  I'll have to ask him whether the feel is improved.  He certainly wasn't impressed when my old floor jack left rust in the trunk (I guess that's the trouble with borrowed tools, eh?)

RE: How Brake System Plumbing Affects Brake "Feel"

The teflon lined, stainless braided hoses I've seen are pretty stiff. Maybe this leads to the perception (or fact) that they have less "give" to them under pressure, thus leading to the better "feel". And as has been mentioned, they cost twice as much, so they "must" be better.
I would think careful sizing of master cylinder vs wheel cylinder, and pads specific to the application, (street/track?) As a previous poster noted (among other things)would have the greatest effect.

RE: How Brake System Plumbing Affects Brake "Feel"

The subject of braided ss brake hose comes up all the time on the motorcycle discussion boards. 99% of the time, the "improved braking feel" mantra is cited. And they have a racing image, which appeals to the "cool crowd". But people are woefully ignorant of the disadvantages of this hose. They are easy to kink if the installation is sloppy and/or the hose is not properly supported. The wire strands are also vunerable to rock damage and other sources of nicks, which can lead to fatigue of the strands. The fabrication process for this type of hose is also critical--it is easy to get some frayed strands that won't seat in the ferule all the way or get some that double over and you won't see this. Leads to either a fatigue failure or a creep type of blow-off somewhere down the road. Finally, the ss braided brake hose have a problem passing the whip test which is part of the SAE J1401 brake hose spec, which is why the OEM's tend to stick with rubber hose.

RE: How Brake System Plumbing Affects Brake "Feel"

A bit more---

Greg, the vintage looking hoses I put on the front of my 23 street roadster are a glass weave with a fiber "braid" covered in a heavy outer "rubber" coating with swedged brass banjo fittings. Pretty high dollar, but "necessary" for the proper look of a 50's hot rod.

Yes, the SS braided PTFE AN -03 is stiff, but, in the right hands is very easy to work with and virtually problem free...IN THE RIGHT HANDS!  They require the proper equipment and training to assemble.  Not difficult when you have done a few.

Lastly, several years ago I updated my inventory as I normally keep a small stock of -03, -06, -08 and, -10 plus a few fittings on the shelf.  The hoses were counterfeit AN hardware from "China"! (If it can happen to Boeing, it can happen to you!)
I've run into counterfeit bolts before, but not hose.  Fortunately it was SOOOO bad we caught it in the shop.

Rod

RE: How Brake System Plumbing Affects Brake "Feel"

My observations as noted on a 60's car with no servo is that the SS externall braided hoses firmed up the pedal very noticeably even though the OEM hoses they replaced were quite new.  OEM hoses that I have cut in the past have been internally glass or nylon braided rather than anything metallic.  Motor cycle ones, especially long ones, may be different though.

To Pats comprehensive list I add the compliance of the pad itself.  Having experimented with 5 different pad materials in the last 2 years on this particular car (having finally run out of the rather excellent but asbestos based OEM pads) I was really surprised at how much difference there was between them.  

Of course it becomes more subjective to assess at this point as you have also the frictional characteristics of the pad coming into to play.  While this doesn't affect the actual pedal travel it will have a strong subjective effect as the brain correlates braking g-force the distance your foot moves and pedal pressure. My personal favourites are actually quite compliant and have excellent bite giving the nicest braking feel and greatest controllability.  

I have have to say that the performance and feel difference between the pads ranging from the cheap motor factors "compressed cardbord/lard composite" efforts to the £100 performance pads I'm now using was nothing short of astounding.  The sad thing is that the expensive ones are little improvement on the original asbestos ones.  The cheap motor factor pads were downright dangerous giving a rock hard pedal and so little bite it was like the onset of pad-fade the whole time.

My point?  I think you will find more difference in braking feel by changing pad compunds than you will by changing hoses.

The compressibilty of the fluid can have a surprisinig effect too.  The most notable variation is with the DoT 5 silicone fluid which is very noticeably "squashy".  I hated it and went back to the real stuff after a week.

Nick

RE: How Brake System Plumbing Affects Brake "Feel"

A major problem with the silicone based brake fluid is the "gassing" of the fluid when things get really hot as in racing or even a long run down the mountain on a curvy road.
Yes, conventional fluid will boil and cause spongy pedal, but at least you have a warning...with silicon fluid you get no such advanced warning...one push you have brakes the next you have nothing!

It did not happen to me, but back in the "good ole days", one of the more notable drivers/writers, Sam Posey, had the problem arise while testing a car at RIR (for a magazine I think).  Going up the hill from T-5 to T-6 the pedal went to the floor and Sam instinctively spun the car, a Ferrari and saved it.  I was standing on the inside of the turn at the time and jumped about ten feet back.  Later in the pits his crew determined it was the brake fluid had overheated and caused the temporary failure.  Some time later SP wrote about it in a tech article that I saved to remind me NEVER to use silicone fluid.

Rod

RE: How Brake System Plumbing Affects Brake "Feel"

Rod--is it possible that water contamination could have been the culprit?

RE: How Brake System Plumbing Affects Brake "Feel"

That happened many years ago.  Subsequent tests have shown it is just inherent with the type of fluid.  I've even heard of it happening on the street...But...you know my old tag line..."believe only half of what you see and none of what you hear".

I'm pretty sure, however, that the car in question was from a notable, pro team and if they were as diligent about the brakes as I am, the fluid would have been new and uncontaminated.  Just a guess.

Rod

RE: How Brake System Plumbing Affects Brake "Feel"

I thought the issues with DOT5 fluid were more about entrained air and cavitation rather than boiling.  Same end result - gas where you need liquid.

Though simply replacing DOT3 with DOT5 may not have evacuated all of the moisture, which would of course boil if you got things hot enough.


Norm

RE: How Brake System Plumbing Affects Brake "Feel"

You have me there, Norm.  I'm not a chemist...I am a racer and in that capacity I would not choose the DOT5 silicone based brake fluid for anything I own.  I have used several brands, Castrol, Motul and such that have boiling temp up near 500f, sufficient for any race car I have ever driven.

http://www.pegasusautoracing.com/ProductSelection.asp?Product=MT600&;iorb=4764

Rod

RE: How Brake System Plumbing Affects Brake "Feel"

I wouldn't use it either, preferring also to stick with what I know will work and what will give the "feel" that I am expecting.  For my newer cars, I'd add the reason that DOT5 apparently doesn't play nice with the ABS bits.


Norm

RE: How Brake System Plumbing Affects Brake "Feel"

Something I read about the silicone stuff was that whereas conventional brake fluid is hygroscopic and readily absorbs water, the silcone does not absorb water. Indeed this is touted as one of it's benefits.

Problem is though, the silicone being less dense than water, any water in the system will sink to the lowest point which could well be the calipers - right where you don't want it, where things get hot.

Conventional fluid will hold the water more uniformly thus needs a larger amount of water to make things dangerous.  I also remember reading (on a brake rebuild specialists website I think) that this free water creates a geater corrosion hazard and is the reason that they will not honour warranties where silicone is used used.

Think I'll stick to the conventional stuff.

Nick

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