Frankenbrakes and brake improvement discussion
- Thread starter Udi
- Start date
RX4-SH caliper will only work with mineral oil brake fluid
RX4-SR caliper will only work with DOT4 or 5.1 brake fluid
See that now, first time I saw them, didn't see the separate P/Ns. I guess I should decide on drivetrain before I order the calipers for my next roadbike.
I think you mean less bite on rotors "with less contact surface area for equal diameter" which I agree with (see below in response to Jm for why "lighter" isn't really correct: you can save weight without reducing contact area). It's why bigger pads tend to have more bite too. Classic friction theory doesn't cover this which is why you'll always have some genius chime in with "friction force = μN, surface area has no impact", but in reality there are small differences due to surface area (particularly for some material combinations) that can indeed be perceptible in static / bite scenarios, and more obvious in dynamic scenarios that involve temporary and permanent deterioration of friction coefficients due to heat.
Aside from that, it's easy to understand this stuff provided you are very specific with which parameters you change. The most important thing (for understanding) is to change only one thing at a time.
- Increase rotor diameter = increased braking force as a direct function of the longer moment arm. Nothing to do with surface area. This increase in force due to leverage is consistent over time (both over a single run and weeks/months). 225mm over 203mm gives a 10% improvement in braking force, this is huge!
- Increase pad and/or rotor surface area = better heat dissipation, less likely to permanently deteriorate pad bite characteristics as a result. Other things like heatsink pads and icetech rotors can improve this further (independently again!). These improvements will have a very different behaviour profile in a dynamic scenario (proportional to usage scenario and time, both time over a run, and over weeks / months of use) which is why it becomes difficult to understand if you don't separate these factors.
If you understand that, you can probably understand why it's nontrivial to "put real numbers on this" - but it should also be (at least partially) clear why a larger diameter rotor provides such a substantial performance improvement that the minor details don't actually matter. The 225mm rotor would be so far superior to a 203mm rotor all round that small details about track surface area will pale in comparison to the clean 10% gain.
But, bigger rotors add a lot of weight, that's why I thought it might be useful to share some actual weights. Equipped with force increase due to leverage (a number) and a weight increase (a number), we can start making objective decisions.
Where exactly did I say that? Oh yeah, I didn't.
Lighter rotors certainly don't = less heat dissipation necessarily either though, that's like saying lighter = weaker. The two Shimano rotors I listed are a classic example, the lighter version uses an alloy core for a roughly equivalent braking surface area so it's both lighter AND better at dissipating heat (since aluminium is better at conducting and radiating heat than steel).
Obviously if you have less contact surface area on an equal diameter and material rotor then yes you'll have inferior dissipation, let's not debate the blatantly obvious.
Awesome question!
I made the spreadsheet a few years ago and the numbers provided at that time were an oval of diameters 25.4mm and 24mm. Initially I calculated the area of an oval based on those diameters, and then just reverse calculated the diameter of a circle with equivalent area for the purposes of the spreadsheet.
However, after looking at the piston, I realised it's not actually an oval!
It's a circle cut in half and extended, so a rectangle in the middle. Obviously this results in a slightly increased area vs. an actual oval, so the final value is still the diameter of an "equivalent area circle" - but now of this new shape.
And yes, the values for the Diretissima (both MC and Slave from memory) currently in the sheet are from Trickstuff - I found conflicting data on the net so I asked directly early this year.
Edit - @Flo33 I added the formula to those cells instead of a constant:
Just had a quick google though, many articles claim "equivalent of 25.4mm diameter", presumably a circle, which doesn't hold true for the 25.8mm claim either. So who knows what is right. I should measure one sometime.
Last edited:
take a break from the shed
These guys got it right!
~400mm front rotor IIRC
~400mm front rotor IIRC
but they at least remembered the "carbon" sticker
I am sure those will come in future kickstarter campaigns.
I'd avoid it.
The Jagwire hoses expand under pressure and tend to have a spongy feel. You can watch them visibly flexing / straightening more than other hoses in my experience. Genuine hoses aren't expensive, and if you have an old Avid/SRAM brake lying around those'll work too (any that use a normal banjo).
Edit - apparently (scroll to bottom of thread) they were updated to fix the issue in 2011/2012 with the "hyflow TF" so it depends how old yours are.
Last edited:
Yes Udi, bringing up frictional resistance increase with increasing real contact area (RCA), due to normal force acting on the surface, is a sign of a true genius. The thing is that typical difference between "classic" contact area and the real one is below 0,1%. That is why no one sane takes it into consideration in most calculations. Those micro effects are irrelevant to real world problems unless You are making some ultra high accuracy stuff. Anyway, as You are a true genius, You should know that real contact area decreases with the speed as well. Friction force is independent of area of contact.
Using bigger pad won't increase the braking power, as the force on the piston is a constant value - thus the pressure on the pad/rotor will drop accordingly. It will help with pad wear and heat management tho.
Last edited:
a) I didn't say it increased braking power
b) I already stated how it helps with heat management
c) We have experienced roughly the same formal education on this topic - let's not keep rehashing it, let's try and learn something new
I just didn't want to completely discredit what maxyedor said - because I've noticed a similar thing myself. It certainly doesn't mean more power, but more initial bite - maybe.
You're assuming that my point was in relation to the difference between "classic" and "real" contact area - which a) it wasn't, and b) may not actually be as negligible as you claim for something like a semi-sintered / organic pad - I think we should find data for the specific scenario before making assumptions.
But anyway, since braking involves conversion of kinetic to heat energy (as we both know, being geniuses), I think it's misleading to imply μ stays constant. It obviously changes with temp (as we both know), but I bet it's not completely stable proportional to applied load either - especially in softer pad materials. If we want to get technical, we should find some graphs on how μ changes for something like a small MTB brake pad under min/max load and min/max temp. I'd be interested to see some data.
Since temp increase starts instantly when you brake, surface area might actually have some interesting implications for μ and thus friction force.
All I was trying to say before though was that bigger rotors have multiple advantages (particularly for increasing power without increasing throw), with the only real disadvantage being weight. I also wanted to point out that less weight doesn't necessarily mean less stopping power, which some people assumed.
Hope by a mile. In fact that orange resi cover on the derissimossissstossispaghetti brakes is the only reason I don't own them.
Oh yeah those are way prettier. Just ordered a set.
or did I?
or did I?
Yeah, I like my brakes cuz they're light. And black. That's the most important part of it. Not having to ever purge them is a bonus.
Bacon.
This isn't exactly complaining about a lack of mid-stroke support, or a crunchy gear shift though. When your brakes aren't slowing you down, or they come to the bar unexpectedly it isn't exactly a trivial matter if you're in serious terrain.
No big deal, just press respawn after you die and buy another set of Shimano levers.
If you go by what Jm_ says, if you die once that's your indicator: it's time for new levers.
If you ignore that 1st warning then you deserve what comes I guess.
oh, it was less aimed at the levers-to-bar-death scenario prevention discussion and more at the .01% gain in rotor weight/24.874663679 round/oval/rectanguarized-diagonally-cross-sectioned-piston diameter one.
Completely solving both problems that toodles mentions (simultaneously and permanently/consistently) actually does require some messing around, unfortunately.oh, it was less aimed at the levers-to-bar-death scenario prevention discussion and more at the .01% gain in rotor weight/24.874663679 round/oval/rectanguarized-diagonally-cross-sectioned-piston diameter one.
Jumping in a nerd thread and making fun of nerds makes you really cool though.
Jagwire hoses and a 9 year old Formula The One is mint. Everything bled up fine and was really good, powerfull, and consistent braking during this weekends race. Why did I stay on that crap XT for so long? Oh yeah...internally routed cables.
I know this was covered somewhat before, but I just want to be clear.
In order to combine my Magura MT5 brake calipers with my Shimano br666 SLX brake levers I;..
1) Simply cut the stock magura hoses down and the levers away effectively,
2) Insert some Shimano barbs and olives in the Magura hoses.
3) Hook that shit back up.
4) Bleed with Shimano mineral oil (does it matter between the magura blood and Shimano mineral oil?).
5) Done?
Cheers!
In order to combine my Magura MT5 brake calipers with my Shimano br666 SLX brake levers I;..
1) Simply cut the stock magura hoses down and the levers away effectively,
2) Insert some Shimano barbs and olives in the Magura hoses.
3) Hook that shit back up.
4) Bleed with Shimano mineral oil (does it matter between the magura blood and Shimano mineral oil?).
5) Done?
Cheers!
You can use Magura barbs and olives, too.
Step 6) wondering what took you so long to do this
Aside from the obvious DOT/Mineral oil issue, but I can change the seals in the calliper to avoid this issue.
Not being a smartarse, but why would you want to? Different power curve? IMO, either go full Trickstuff or nah. The Trickstuff caliper is dope (for a low-end non-monoblock
) and the finishing is amazing.I'm really keen now to upgrade to try the V4 caliper with the E4 nylon lines and see how mushy it is/if at all. Most of the weight difference between the V4 and E4 system is actually the braided lines, with less than 10g difference in the caliper and pads. Trickstuff do some kevlar reinforced nylon line wizardry which might make the V4/nylon line combination a great all-round brake, but its a gamble setting it all up. The thicker wall size Saint/Zee line might be enough as well.
Why on earth would You do that?
Yes, terrible idea.
- Hydraulic leverage ratio is way off, lever stroke will be too long / dangerous under heavy use.
- Obvious DOT/mineral issue, it's not that easy to match brake seals given that piston rollback is a function of seal geometry.
- Piston rollback - this is one of the parameters that allows Trickstuff to build a superior brake, a reduced and very tightly toleranced rollback value.
If you want Direttissimas, buy Direttissimas.
Ze Germans mix Direttissima levers with Magura calipers, see here https://www.mtb-news.de/forum/t/trigura-how-to-direttissima-pumpe-und-mt5-sattel.820819/ and it is apparently approved by Mr. Tr!ckstuff himself...
For the record, ich spreche keine Deutsch, so don't ask me!
For the record, ich spreche keine Deutsch, so don't ask me!
Zee levers are $25/piece. Just saying.Ze Germans mix Direttissima levers with Magura calipers, see here https://www.mtb-news.de/forum/t/trigura-how-to-direttissima-pumpe-und-mt5-sattel.820819/ and it is apparently approved by Mr. Tr!ckstuff himself...
For the record, ich spreche keine Deutsch, so don't ask me!
Just as a general safety warning - many combinations will appear to work initially when constructed and bled, however if the hydraulic leverage ratio is changed significantly there can be problems after some usage time. If the hydraulic leverage is decreased the brake will just lack power, but if it's increased, the throw may reach dangerously long levels when used for some time and/or when used as a rear brake (which is more prone to throw increasing over time for various reasons, especially on lower quality master cylinder assemblies).
Keep in mind that if a system is overfilled it can give a temporary decrease in lever stroke (which fools people into thinking all is OK), but a) this makes the brake behave as a closed system (which is dangerous), and most manufacturers account for this by using very weak reservoir sealing, so b) the excess fluid will quickly just leak out over a couple rides and the throw will reach its default state defined by the leverage.
Throw change due to lever/MC swap is defined mechanically (lever geometry), hydraulically (mc piston diam), and by free stroke before the timing port is shut; and at the caliper it is defined hydraulically (slave piston diam/s) and by piston rollback distance. There are a LOT of variables that should be considered to calculate the power change and throw change, and safety in general.
I just thought I'd mention this stuff somewhere if people are actually trying combinations, might save a crash.
M810s are good in my experience, occasionally you'd get a dud lever but I ran them for years without complaints apart from the lever throw being quite long (and getting a bit longer over the years). They are a very powerful brake too.
If you can stretch the budget, Hope V4s are a very solid option and readily available where you are.
Great if they work for you (I gather they do) but the money in the more expensive gear is definitely utilised and justified.
Keep in mind that if a system is overfilled it can give a temporary decrease in lever stroke (which fools people into thinking all is OK), but a) this makes the brake behave as a closed system (which is dangerous), and most manufacturers account for this by using very weak reservoir sealing, so b) the excess fluid will quickly just leak out over a couple rides and the throw will reach its default state defined by the leverage.
Throw change due to lever/MC swap is defined mechanically (lever geometry), hydraulically (mc piston diam), and by free stroke before the timing port is shut; and at the caliper it is defined hydraulically (slave piston diam/s) and by piston rollback distance. There are a LOT of variables that should be considered to calculate the power change and throw change, and safety in general.
I just thought I'd mention this stuff somewhere if people are actually trying combinations, might save a crash.
Skip the Quadiems, I would not bother.
M810s are good in my experience, occasionally you'd get a dud lever but I ran them for years without complaints apart from the lever throw being quite long (and getting a bit longer over the years). They are a very powerful brake too.
If you can stretch the budget, Hope V4s are a very solid option and readily available where you are.
With materials, design, and build quality proportional to the price.
Great if they work for you (I gather they do) but the money in the more expensive gear is definitely utilised and justified.
This would be OK with only the 2-pot Magura caliper (22mm x2), definitely NOT with the 4-pot calipers. Also Magura blood has some pretty rubbish properties, so as a general PSA, use Shimano mineral oil (or something superior) for oil brakes.Ze Germans mix Direttissima levers with Magura calipers, see here https://www.mtb-news.de/forum/t/trigura-how-to-direttissima-pumpe-und-mt5-sattel.820819/ and it is apparently approved by Mr. Tr!ckstuff himself...
For the record, ich spreche keine Deutsch, so don't ask me!
Obviously they wouldn't use a fluid that was unsafe / inadequate, but the Magura fluid has a substantially lower boiling point than most brake fluids from the numbers I've seen (120*C / 248*F) and when questioned on the topic they provided very little data or useful information. I've heard that it's rebadged Castrol Vitamol V10 but haven't seen this actually confirmed by Magura so who knows.I wouldn't mind if you could take some time and write more about that, specially considering that my Shigura are at the moment bled with royal blood...
Either way, the Shimano fluid at least has the BP published (280*C / 536*F) and sufficiently low viscosity.
Certainly no need to rush out and change it, I just prefer to have some numerical data on what I'm using.