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I'd be curious to hear more about the other adjustment.
I feel like your ~17mm free stroke sounds pretty typical with my Dominions. It definitely gets longer as pads wear, which is somewhat of a nuisance because the contact point difference between front and rear for me becomes annoying when the rear pads are at like 50% life. The one thing I loved about Codes was that the contact point adjuster did something (and didn't affect lever reach), so I could use it to compensate for pad wear.
What brakes pads are you guys running on the Dominion A4?
I'm finding the metallic/sintered pads really noisy. When the brakes are cold they squeal pretty bad. It takes 2-3 lever pulls for the noise to go away. I'm guessing this is normal? The noise is pretty much gone once they're hot. Power and and bite point also increase dramatically when hot compared to cold. I personally find this pretty annoying.
Also, any recommendations for aftermarket pads with similar power but less noise? I've head good things about Galfer Green, but they seem they wear pretty quickly. MTX gold maybe?
I love my Galfer purple pads and won’t touch anything else.
I'm using Galfer Greens, wear fast for sure but performance is great.
The Hayes sintered have good bite & power and durability but are noisy, especially wet. The Hayes semi-mets (black) have nice modulation and are a lot quieter, but don't last as long, especially in the rear. Galfer green bed in super quick, have a ton of power and modulation, run really quiet, but wear out really fast in the rear (and faster than Hayes semi-met in front). I also ordered a bunch of Galfer purples (from Europe, for some reason the US distributors don't have them) but am waiting to finish off my current pads before I try them.
Since Dominion free stroke gets longer with pad wear, my preference is to run semi-metallics (Hayes black or Galfer green) front, sintered (Hayes copper or Galfer purple) rear for the best modulation and consistent braking feel.
That is an interesting take on things. I have heard that there is a surprising amount of dissolved air in mineral oil, right out of the bottle, so it makes sense that one could dissolve more into it if kept under pressure, and the bubbles (assuming a decent bleed in the first place) would be such a trivial amount that the percentage change would be minimal. There is the double edged sword though, as you mention, of the gas coming back out once pressure is released, and it would be really interesting to know how long that takes.
As Primoz mentions further down the thread, I have heard of people de-gassing their fluid under vacuum before filling their brake system with it, in order to prevent the emergence of bubbles as the gas comes out of solution, so if this solution/dissolution is really going on to a meaningful degree, then that preliminary step, to minimize the gas content of the oil at the outset, makes even more sense as a preventative/enhancement.
How do you go about degassing it? Are you just talking about pulling a quick vacuum in a high quality syringe, or do you have some other apparatus and do it for longer?
I have heard surprising claims about the amount of dissolved air contained in mineral oil (not sure if this would apply to DOT fluid too) and have always wondered how long it would take to fully purge it. If you think about opening a carbonated soda/water bottle, once the pressure is lowered, the Co2 starts to be released, but it takes quite a while (hours and hours) for it to go completely "flat", and I wouldn't be surprised if you put it under a vacuum if you found that there was a lot more dissolved gas that still remained even after the bubbles had ceased at normal atmospheric pressure.
Just using the the nicer SRAM bleed kit, I'll degas the DOT 4 fluid before bleeding by pulling a vacuum in the syringes.
There is a surprising amount of gas in the fluid. I'll spend as much time degassing as it takes to do the rest of the bleed.
I have considered building a vacuum chamber to degas, but haven't (yet).
Glycol ether (primary component of dot 4 and 5.1 brake fluid) contains approximately 19% dissolved atmosphere at STP. Most liquids contain some percentage of dissolved atm with alcohols typically containing more. Short of sparging with helium, vacuum degassing is the most effective method of dissolved gas removal. The soda bottle is somewhat different because it is supersaturated with co2 as a method of generating fizzy bubbles. Yes as the pressure is released the gas content decreases but once it’s done or reached is pressure equilibrium there is still 10 percent dissolved atmosphere in the liquid (approx, just guessing on this). Vacuum degassing in the syringe prior to bleeding brakes or suspension will have the most appreciable effect on getting you the best bleed, even a good bleed without vacuum degassing will be mediocre at best due to the dissolved gas content stored by the glycol ether. This is a rather interesting discussion to me as I work as an r&d ME in the bio-analytics instrument design field developing active solvent degassing systems. Always wondered if some of our equipment could be used for fluid degassing for brakes and suspension…
I took some pictures of the procedure last night I’ll try to post something up tonight or tomorrow. You can get much less than 17mm but I like the feel where I am at. I personally haven’t really noticed wandering bite at the pads wear, I’ve been through 3 sets so far about to go on number 4.
I find this all interesting, and I'm learning some stuff/doing more reading. So please correct me when I go off the rails here.
Degassing should/could do two things.
1) Reduce the amount of entrained air that might appear in future (depending upon how well sealed the system is over long periods of time). This seems boring. Entrained gas follows Boyle's law and is very bad for brake feel/performance. It's what we should all be fighting, probably.
2) The more interesting discussion at the moment. Dissolved gases. These do not follow Boyle's law and do not have a big impact on braking. This dissolved gas impacts the stiffness of the fluid, that is the bulk modulus. I read some studies that suggest some well degassed hydraulic fluid had twice the bulk modulus of sample with significant/normal from atmosphere. So to quantify this, lets do a quick calculation.
What is the change in volume of degassed hydraulic fluid for a pressure change of 2000psi and a volume of 30ml for a fluid with a bulk modulus of 260,000psi.
I picked those numbers because I can get 2000psi out of my MT7 Levers with a good pull, and from bleeding experience it seems that passing 30ml of fluid through the system is enough to purge all the old darker fluid for new fluid. I think they're both reasonable ballparks.
Let's use this calculator: https://www.ajdesigner.com/phppressure/fluid_pressure_equation_bulk_mod…
Results: Change in volume of 0.23ml.
The function is linear, so if we had sample hydraulic fluid with lots of air in it such that the bulk modulus dropped all the way to 100,000psi. We'd see 0.60ml of volume change.
Interpretation the result, how much movement of the master cylinder is required to account for this fluid compression? Let's use a Magura MT7 lever as an example. It has a 10mm piston diameter. 0.23ml volume/(0.5cm^2*3.14159 piston area) = 0.292cm, 2.92mm.
2.92mm to account for the fluid compression of reasonably air free hydraulic fluid. That feels cursed, I hate that a lot. Someone find an error in that math. It's even worse if you think about the fluid that is full of air and has 2.6x less bulk modulus, the travel is ~7.6mm then. Ugh.
In my brain before doing that math I was expecting fluid stiffness to be a miniscule factor and that all you pre-bleed de-gassing people were nuts and that it was just a way to cope with the fact that you weren't actually getting all the entrained air out and by having a fluid with less dissolved air in it, it would more easily absorb the entrained air left behind thus producing a decent bleed/lever feel still.
I though the impact would be less than the volume increase in the brake lines under pressure, but now it seems like both those things are probably around the same magnitude (but I don't have any great data about MTB brake line stiffness currently). Someone tell me I've made a math error and the fluid is actually much stiffer or I'll have to fall down a rabbit hole of finding the brake fluid with the highest bulk modulus and start doing the best de-gassing ever (the vacuum chamber is already on the amazon truck).
** I know I've massively simplified bulk modulus as there are temperature, pressure and other things that affect it as well. I had to pick some values to compare with though. If anyone thinks that I haven't picked good values, please propose some others.
Mostly this. We have talked about making a vacuuming device that would hook up straight to the brakes for Sram brakes. Attach a vacuum pump to the lever, attach a a reservoir to the caliper with oil in it and a valve, then apply vacuum to the lever and periodically add oil to the system to replace the air degassed from the fluid.
I also take a lot of time to bleed Sram brakes lately and only apply vacuum on either side (rarely pressure) to pull the fluid through the system together with all the bubbles. The negative is that too much vacuum pulls air past the outer seal on the lever I think.
As for mineral oil (suspension fluid), it appears to be very similar to dot out of the box.
Regarding bulk modulus, modulation will be a factor of bulk modulus and stiffness of the system - line, lever system, caliper.
As for stiffest fluid, it seems to me dot brakes have more modulation than mineral oil ones? Can it be related to the fluid properties?
Even tho i'm sold on getting new brakes, i would actually be curious to do some mineral oil testing,
https://www.radicperformance.com/brake-fluid-tech#:~:text=MAXIMA%20MINE…
some data from the Radic Website, just by looking at this i feel the best one is the Bionol, but being always unavailable i'd go for the easy to get Gold Idraulic Oil, it's very low viscosity and high boiling point, the one i'd get last is the Plutoline which is not even a brake fluid, with a flashpoint ultra low compared to everything else, although is the choice of Intend for some reason, opposite way compared to the oil chosen by Trickstuff,
Has anyone tried any of these fluids? and compared to what you had before could you feel the difference?
I've tried bionol, putoline and maxima , tbh I didn't notice any difference. I haven't had bionol filled brakes hot enough to fade mind you.
Get whatevers easier/cheaper. I've used putoline the most of all. I reckon it's cheaper cos it's NOT listed as a brake fluid haha. Putoline in 1l was like 40 bucks NZ delivered haha.
I still don't understand why people hate DOT so much when it's so much easier than faffing about with different mineral oils...
How is it any easier? There are lots of DOT fluids that exceed their standards. The standards only specify a set of minimum characteristics. Manufacturers are free to make products that exceed the minimum standard, which leads to the exact same place as people trying to figure out which mineral oil is best.
And most of those mineral fluids sting a lot less if they end up in your face than DOT fluids. But I haven't sampled all of them yet.
i was curious, Plutoline is also recommended by the local brand Radic on their brakes, i don't understand how can it be good given that it will likely get hotter than 87 degrees for sure, i keep using the royal blood as i have it but was actually curious if a fluid with lower viscosity would improve the performances somehow
all i know is that if Hopes were mineral they would’ve been on my bike since they came out probably
Easy. Go to the first automotive shop and buy a flask of dot 5.1 fluid. Job done.
Not sure about the face (haven't had a shot of dot to my eyes yet, but for the hands it's different but same, it's best not to get covered if possible. Plus dot is neutralised with water so cleanup is easy.
Then Mineral oil brakes are equally easy? Go to the bike store and buy the mineral oil sold by your brand of brakes. Job Done.
Agreed with Primoz. Thanks to the automotive industry, DOT fluids are compliant with international (ISO 4925) and national standards and it should be the same regardless of the brand label on the bottle. You can pick this stuff up from gas stations. There is no such thing for mineral oils. Each brake manufacture recommends their own concoction of a colorful mineral liquid. They can differ in viscosity, thermal ceilings etc. etc.
I don't know why people complain about DOT fluid. If you are a half decent non-clumsy mechanic, you don't have to worry about splashing it around on paintwork or your eyes. Spray your parts down with water after wrenching and you're good to go.
maybe read what is actually written?
„The actual boiling point is unspecified. Flashpoint is 87°C.“
Putoline: >180°C
https://www.putoline.com/downloads/PF_20_09-GB.pdf
does that answer my question? Nope, now we know it's below 180 degrees so less than half compared to Gold and Bionol
nope, you read it wrong again, its above 180°C. where did you go to school?
The lowest numbers I typically see for mineral oils, just from browsing around, are around 150 Celsius for a flash point, and in the high 200s Celsius for a boiling point, so that Putoline must have some particularly volatile components added to have such a low flash (87) and perhaps boiling (some undetermined number north of 180). Not saying that is a problem, as many people seem to be using it successfully, and maybe there is some advantage to those additives in terms of the other performance properties (consistent viscosity at lower temps, easier bleeding due to anti foaming additives) of the fluid, but it does give one pause. It would be interesting to know why Intend uses it, given Cornelius' past experience with Bionol, which many people seem to think is the class leader.
Do you know what the transparent portion of the bars are for the Bionol and Gold oil on the left side of the comparison chart? Its similar to the way that Radic displays a wet/dry temp for DOT 5.1 on the right, but moisture shouldn't really be a factor for the oils. I'd thought it might have something to do with the flash point, as the entire Putoline bar is transparent, but there is no mention of that.
That is an awesome thought experiment, and much credit to you for basing it on some potentially realistic numbers! Like you, I had assumed fluid stiffness was a trivially low component of the overall picture, and was mainly concerned with using a vacuum to help remove entrained micro-bubbles. If your numbers are even close to accurate, it does really give one pause, as it seems like degassing could offer some serious potential to firm up the feel at the lever while maintaining max power, which could be really desirable for some people/braking systems. Do you have any idea how long it would take to remove the majority of the dissolved gasses, under a realistically achievable vacuum in a workshop setting?
This conversation motivated me to mess with the Cura 4s a bit more. I took some zip ties that came with one of my bleed kits and I strapped the levers down nearly to the bar. I left it like that for a few hours and pulled it off, I can barely pull the lever to the bar by hand anymore, before it was going all the way to the bar.
I'll rebleed tomorrow and ride them around to see if the feel changes
afaik it was first mentioned by some on mtb-news.de forum as a cure for wandering bite point in shimano brakes.
Post a reply to: Nerding out on Brakes shall we? Not another tech deraliment