R6 Brakes - Lets Talk Numbers

[bmccrary]

So a few weeks back I was riding up in the Boone and making a few passes down Hwy 421, "The Snake." On the way down I was chasing a guy on a SM and towards the bottom of the run I started loosing the front brakes momentarily, mid-corner. I know that I wasn't boiling the fluid as I just replaced it with Motul this past winter, and feel wasn't going away completely. For a moment as I was just about to release the front and continue to to trail brake, the lever would fall a touch and the amount of load I had on the front tire due to braking would decrease. I also want to note that the brakes worked fine again if I just released the lever and then pulled again.

From what I have heard on here before, it sounds like what I may have been experiencing was the swelling of those rubber brake lines. Any one want to confirm this with similar experiences?

For my senior design project this year I am going to be building a single wheeled trailer to pull behind the FZ. (Ill save that info for another post)
But I am looking to upgrade the brakes this winter with SS lines and possibly replace the stock m/c with a an R6 m/c (standard or radial). The plan is to tag this mod into the budget for my senior design as a safety upgrade for pulling a load. (In addition to this, maybe a Ohlin's shock too? )

But anyway, I have been doing some research on braking and the math that follows suit.

"M/C bore area summary: The bigger the area of the bore, the less pressure is generated for a given input lever force. The smaller the bore area, the more pressure can be generated from that same input force"

"M/C volume summary: The bigger the area of the bore, the less stroke required to move a given volume. The smaller the bore area, the more stroke is required to move that same volume."

So the battle is over the amount of motion in the lever vs. the amount of feel in the lever...

I need to put together some numbers to compare the volume of the m/c's as well as get some numbers on the surface area of the pistons within the calipers to do an honest comparison.

Just wanted to know if anyone has an extra m/c laying around, stock or R6 as well as an extra caliper (04'-06') that I could possibly borrow for measurement. I will gladly pay for shipping in both directions and will send it back to you, ASAP.

I personally know these mod's will help the bike tremendously, but I need to prove their performance in MathCAD to my professors as they have never ridden a day in their life. And as always you guys will get the end results as to what I find.

Thanks guys!

-bryan

 

[Cali rider]

This is a classic example of a master cylinder seal failure. Pressure is built up at the lip of the seal and it yields just a fraction of a c.c. of fluid back in to the reservoir. The result is exactly what you described, a loss of pressure. It isn't hose swelling.

The cure: rebuild the M/C for about $25. Be SURE to flush all of the old fluid.

 

[RJ2112]

All you really need to know, are a specific set of piston's area, and the bore of your MCs for comparison.

I was fiddling about with that info a while back, and used calipers from the Brembo site to get the specs for the caliper bores. You can do the same for the master cylinders.

Knowing the pads are going to move about .020" between 'rest' and full application gives you the volume of fluid that needs to change position. That tells you the volume that has to move in the master cylinder, which gives you the piston stroke. That, mulitplied by the mechanical advantage of the brake lever will translate to the force applied, once contact is made.

 

[bmccrary]

This is a classic example of a master cylinder seal failure. Pressure is built up at the lip of the seal and it yields just a fraction of a c.c. of fluid back in to the reservoir. The result is exactly what you described, a loss of pressure. It isn't hose swelling.

The cure: rebuild the M/C for about $25. Be SURE to flush all of the old fluid.

Cali,

Thanks for the response I will look into that and see what I can find. I have a feeling though I wont be able to see such damage as it will probably be very minimal. Thank you for the information.

Would you mind describing a scenario when the brake lines swell? Just curious about that?

-bryan

 

[bmccrary]

All you really need to know, are a specific set of piston's area, and the bore of your MCs for comparison.

I was fiddling about with that info a while back, and used calipers from the Brembo site to get the specs for the caliper bores. You can do the same for the master cylinders.

Knowing the pads are going to move about .020" between 'rest' and full application gives you the volume of fluid that needs to change position. That tells you the volume that has to move in the master cylinder, which gives you the piston stroke. That, mulitplied by the mechanical advantage of the brake lever will translate to the force applied, once contact is made.

RJ,

Great information, thank you.

I understand where you are coming from, and that explains the formulas for the calculation perfectly. However, the stroke and bore size is where the adjustment and compensation between force and feel comes in.

As to the mechanical advantage of the lever, this is where the radial m/c's comes in. From everything I have gathered, they are designed to maintain constant force all the way through the pull. As apposed to the standard m/c's, were due to the moment arm and the way the plunger system is attached to the lever you do not get a linear pull across the stroke. If that makes since...

Thanks again for the info!

I still need to get some measurements though unless brembo has all the specs needed. I guess I just need to figure out what the model numbers are on our stock m/c is and what it is for the r6 m/c.

(any one know what year Yamaha started putting the radial m/c on the R6 or R1)

 

[RJ2112]

A bit long winded; hopefully it contributes for you....

I went to the Brembo site, due to the rear master cylinder being a Brembo part. Looked up the parts that were applicible to an FZ6, and went from there. Shouldn't be too hard to suss out what they would use on a R6 or FZ1.

I was looking at two things; both of which may relate to where you're going. The discussion started concerning someone who claimed a different 'feel' for running .2mm ID brake lines giving a 'stiffer' feel.

I ran calculations to determine how that smaller than OEM line diameter affected fluid flow between the MC and the brake caliper. As I built it up in excel, I could play with the bores, and line diameters, and see how far through the lines the displaced fluid volume had to move to actuate the slave pistons. I converted that to Word, and attached it. Shoot me a PM if you have any questions.

I'm still up in the air on the whole radial MC/radial caliper stuff. I don't get it at the caliper end.... essentially we're talking about mounting the caliper at an angle, on a structure. The structure has to be just as beefy as the caliper was in previous designs.... so it seems to me on the caliper end all you are doing is moving the mass to the end of the fork rather than the caliper. As the two are intimately associated.... it makes no difference in unsprung mass.

At the MC end... I can see that the lever travel is a more direct linkage to the MC piston, and that should result in a more linear response. The part I am unsure of, is whether the human hand can detect the difference.

Having worked with $1500 digital pull scales, I know how non-linear most sliding systems are. Particularly anything with stiction.

In this system, we're talking about 9 O rings, in 9 different bores.... 8 moving about .020", one moving ~ 10mm (MC). When you factor in line flex (big effect), linkage deflections, system 'slop' at the pivots...... it's pretty difficult to catagorically state that the linkage change is the most important part of 'feel'.

 

[Speedygonzales]

If you have a 2005 FZ6, then you'll have the 2 pot calipers.
So using the standard R6 MC isn't such a great idea.
The R6 is using 4pot's so it needs a different MC than an 2pot setup.

I know you can buy a Radial Nissin MC diam 17, which is more suited for a 2pot setup. The most radial MC are 19mm for the common 4pot setup of modern bike's.

BUT ...

After talking to my local Yamaha dealer, he said. Don't bother on the FZ6, the standard MC is good enough. And I bought a set of EBC HH brakepads instead.
I already run HEL brake lines and now with the new pads I don't really see the need for a Radial MC. I'll save the money for other things.

I would sugest to fit some steel brake lines and new brake fluid (you can try using "race" fluid), it wil make a big difference!

 

[bmccrary]

A bit long winded; hopefully it contributes for you....

I went to the Brembo site, due to the rear master cylinder being a Brembo part. Looked up the parts that were applicible to an FZ6, and went from there. Shouldn't be too hard to suss out what they would use on a R6 or FZ1.

I was looking at two things; both of which may relate to where you're going. The discussion started concerning someone who claimed a different 'feel' for running .2mm ID brake lines giving a 'stiffer' feel.

I ran calculations to determine how that smaller than OEM line diameter affected fluid flow between the MC and the brake caliper. As I built it up in excel, I could play with the bores, and line diameters, and see how far through the lines the displaced fluid volume had to move to actuate the slave pistons. I converted that to Word, and attached it. Shoot me a PM if you have any questions.

I'm still up in the air on the whole radial MC/radial caliper stuff. I don't get it at the caliper end.... essentially we're talking about mounting the caliper at an angle, on a structure. The structure has to be just as beefy as the caliper was in previous designs.... so it seems to me on the caliper end all you are doing is moving the mass to the end of the fork rather than the caliper. As the two are intimately associated.... it makes no difference in unsprung mass.

At the MC end... I can see that the lever travel is a more direct linkage to the MC piston, and that should result in a more linear response. The part I am unsure of, is whether the human hand can detect the difference.

Having worked with $1500 digital pull scales, I know how non-linear most sliding systems are. Particularly anything with stiction.

In this system, we're talking about 9 O rings, in 9 different bores.... 8 moving about .020", one moving ~ 10mm (MC). When you factor in line flex (big effect), linkage deflections, system 'slop' at the pivots...... it's pretty difficult to catagorically state that the linkage change is the most important part of 'feel'.

Yes Like I said, I am not so sure that moving to radial master cyclinder is the right choice. But it wouldnt hurt to do those calculations. Thank you for the information you provided. I greatly apprectiate it! Not sure where you were going with the caliper thing, but I have no intentions on swaping calipers or rotors for that matter.

Last summer I flushed my brake system completely and replaced what ever fluid that was in there with Motul RBF 600. That alone made a huge difference in the feel of the brakes. Then again this winter I flushed the system again as Dad and I were using up the last of a bottle we opened to use on his bike at the time.

-bryan

 

[Motogiro]

This is a classic example of a master cylinder seal failure. Pressure is built up at the lip of the seal and it yields just a fraction of a c.c. of fluid back in to the reservoir. The result is exactly what you described, a loss of pressure. It isn't hose swelling.

The cure: rebuild the M/C for about $25. Be SURE to flush all of the old fluid.

That was my first thought....Had it happen after I pushed the pistons back on a caliper and instead of opening the bleed valve on the caliper I pushed dirty fluid back toward the reservoir and had the same intermittent, then steady failure of the master cylinder.

Have heard of FZ6's getting spongy brakes but I haven't experienced it yet. I do keep my fluid fresh.

Cliff

 

[wrightme43]

opcorn: Sittin and diggin man. Just checking in.

 

[RJ2112]

The biggest improvement you can make is to go to braided lines, followed by better pads... about that time, getting better fork springs is due as well.

With the line calculations, I was getting a feel for how far down the line the fluid expressed from the MC had to move to change the volume at the caliper. The smaller the ID of the line, the further the fluid has to travel. More opportunity for there to be friction with the sidewalls whne you get to really small..... but I've been told that's a non-issue. The calculations make me suspect otherwise.

Once the pads make contact with the rotor, there is effectively no more fluid movement.... except in the case of OEM brake lines which will expand some amount under force. If the line is a meter long, and expands by 10%.... there's some number of cc's of fluid that are not pushing on the rotor. The jacketed lines prevent that expansion... cut it down to 1% or so. More of the work at the lever gets to the rotor.

Going to an R1 MC is one of the modder's choices when 'upgrading' the brakes.... on that self same theory that a bigger bore means less lever movement to displace the required fluid, and the ratio between caliper bores and MC is changed. Seems to me the bigger bore would make for a 'softer' touch... there has to be some loss of leverage when you make the MC bore bigger, so the ham fisted would not quite as readily lock the rotor.

 

[Cali rider]

I found this document online. It has some interesting stats, but the report was generated by the manufacturer so bias is quite possible.

http://bin.motorarte.com/marcas/goodridge/Goodridge_TechReport.pdf

In addition, here is another solid summary on the pros/cons of braided lines:
Brake Lines - NSX-Wiki

 

[RJ2112]

I found this document online. It has some interesting stats, but the report was generated by the manufacturer so bias is quite possible.

http://bin.motorarte.com/marcas/goodridge/Goodridge_TechReport.pdf

In addition, here is another solid summary on the pros/cons of braided lines:
Brake Lines - NSX-Wiki

Interesting.... I like the Goodrich report, as there was delta between sample sets. I have more faith in data that has variance. Anywhere from 100 psi to near 1000 psi increased burst protection. The expansion is documented with a rubber line, it's a beyotch to quantify... but they did a pretty good job. They did use an outside test lab to confirm their data, as well. In formal reporting, there would be an addendum providing that document as part of the package.....

The NSX stuff...... that's a good testament to avoid buying crappy lines.

Considering most automotive systems are 80% or more metal tubing with no flex involved.... the proportion of the line that is flexible is quite small. Just the portion from the wheel well to the caliper.... probably half the distance of an MC (fork) line with more than 10 feet of tubing on the chassis that has zero flex.

The less joints there are in the lines, the less opportunity for leaks and structural issues. It was a bear bleeding my lines, due to that daisy chain line that passes over the fender to feed the left caliper. That upside down U trap captures bubbles. It's tough to bleed that and chase the bubbles into the left caliper to exit the zirc fitting.

I'm liking the braided setups that run individual lines to each caliper.... no U trap.

 

[Speedygonzales]

2 lines from the MC to the calipers is the best setup. It might not look as clean ... but who cares.

And for the guy's who want to change their MC, make sure you get the right bore. The bigger the bore, the less movement you need to make with the lever. But also the less feel you get. Riding in the rain you really don't want to get from no brakes to full lock in 1cm lever movement.
The 20mm radial's are for race or 6pot setups.

I was really looking for a radial MC, but changing to EBC HH and moving the lever more to the center of the handlebars ( so I have a bit more leveridge ). I feel the need for a radial MC te be less. Since the standard MC isn't a bad one, it has nice feel.

 

[bmccrary]

Everyone, thanks for the info! It is always good to have an informative thread...

Hopefully in the next couple evenings I will be able to start building a mathCAD file to start crunching numbers with.

I am for sure going to upgrade to the SS lines, I imagine I will stay with the stock line size I really dont see how increasing or decreasing line ID will make much of a difference. However I think going with a smaller line would increase the chance of boiling the fluid... less volume in the lines.

As far as the mastercylinder goes, I am not sure exactly which route to go. I would like to get dimensions first as to what size it is (bore and stroke) and go from there. I would perfer to keep a longer stroke as opposed to a large bore. Touchy brakes are never good... Just want to get numbers to see where I am now. However I sit here thinking back to the last time I had the bike out for any length of time, I remember noticing how much I had to pull the lever in to get the bike to stop coming up to a stop light. With that in mind, stepping up in bore size a bit might not be so bad.

-bryan

 

[abacall]

This is a classic example of a master cylinder seal failure. Pressure is built up at the lip of the seal and it yields just a fraction of a c.c. of fluid back in to the reservoir. The result is exactly what you described, a loss of pressure. It isn't hose swelling.

The cure: rebuild the M/C for about $25. Be SURE to flush all of the old fluid.

I just had this problem in my Subaru. It feels exactly as you described.

Line bulging feels much different, more like slight loss of pressure on hard braking application. When you use SS lines you mostly feel the difference under hard braking, a more direct feel.

I did however replace my MC in the Subaru for the same reason. With larger MC I noticed a firmer pedal with quicker response, but a slight loss of modulation. I imagine the result would feel the same on the bike. But with the adjustable lever, I don't see the need. You can dial up response at the lever, and still have all the modulation of the OE MC.
I say rebuild the MC, get some lines.
One thing you may have overlooked is pads. Pads can help dissipate heat and allow for quicker bite and less fade.

 

[gusss]

I had spongie lever on my 2008 fz6.....
Changed fluid, it got better..
But I think I'm doing a lot of hard braking,......
I'm not happy with my brakes, I think i'll go with the braided ss lines...

My hand is getting really tired!!!!

 

[TownsendsFJR1300]

I recently replaced my rubber lines on my 07 with braided SS HEL lines (front and back). There is a huge difference.

Before, with the rubber lines, you could pull the lever in a good half way before full stop and somewhat mushy(from expansion). Now, maybe 1/3 to 1/4 and they are rock solid! I could probably do a "stoppie" now (but don't have the balls to squeeze the the lever that hard)....

Note: I did, several months ago, take apart and clean both front calibers/seals (they weren't bad), flush and bleed. The pads are original OEM with 6k miles on em...

At this point, I wouldn't want anymore braking power, if there's traction, it WILL stop!


Scott