Know-How


Encyclopedia


We created this encyclopedia because of the many truths and untruths about disc brakes that are out there. In this encyclopedia we explain the fundamental terms and give our view on some related topics. Some readers may think of the terms as trivial, others will perceive them to be too technical. We don’t claim that this encyclopedia is complete. In case you spot a mistake, please feel free to contact and correct us.


In charge of the encyclopedia: Klaus Liedler.

 

2-Pistons vs. 4-Pistons


Is there something that actually speaks for a brake caliper with 4 pistons instead of 2? To tell the truth at the very beginning: It is not as simple as because 4 pistons create double the brake power compared to 2. It is not the number of pistons, but the total surface of the pistons that stand for more or less power (all other parameters like surface of the BMC piston and mechanical ratio of the BMC kept on the same level). The real answer is: evenness of the contact pressure. You may know this effect, namely that the brake pads are being pulled in when pressed against the rim, from V-brakes. This worsens the modulation and results in squealing. In order to compensate for this effect the brake pads of V-brakes are installed in a slightly slanted position. A similar effect occurs in case of disc brakes. Braking produces a torque (resulting from the disc rotor’s rotation) which presses the brake pad on the inlet side (i.e. the side where the disc rotor runs into the brake caliper) to the disc rotor. If this effect is not balanced out, it results in uneven contact pressure, the brake’s performance decreases, and the wear and tear of the brake pads increases. There are several possibilities for balancing it out. A 4-piston brake caliper is the neatest option technically. In case of 4 pistons every single brake pad is pressed to the disc rotor by two caliper pistons that differ in diameter. The pistons on the inlet side are smaller than those on the outlet side.The force a piston applies pressure with depends on its diameter or surface. Thus, there is less pressure on the inlet side than on the outlet side (where the bigger pistons operate). However, contact pressure is evenly distributed on the brake pad as it is being pulled in on the inlet side which additionally presses it to the disc rotor. The difficulty in designing a 4-piston brake caliper lies in the calculation of occurring torques which is necessary to determine the ratio of the pistons’ diameters. Thus, a 4-piston brake caliper doesn’t work better because the number of pistons is doubled but because it guarantees equal contact pressure of the brake pads. This has a positive influence on the brake’s performance and it reduces the danger of noise and squealing.

Note: A 4-piston brake caliper that consists of 4 individual brake pads makes no difference to putting together two 2-piston brake calipers. In fact, this would completely waste the advantages of 4 pistons.


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Adjustment of Free Stroke


This is often called “Pressure Point Adjustment” (e.g. Avid, Formula). Calling it that is plain wrong because when free stroke adjustment is applied, the brake lever’s pressure point (i.e. the position of lever in relation to handlebars in which the brake pads touch the disc rotor) isn’t adjusted. However, adjustment of free stroke shifts the distance from the primary seal’s front edge to the reservoir port inside the brake master cylinder. In case of a brake without free stroke adjustment, this distance should be as small as possible, near to zero. This distance varies by applying the free stroke adjustment. If free stroke is enlarged, the caliper pistons inside of the brake caliper don’t move despite actuation of the brake lever until the primary seal has coated and sealed the reservoir port and finally starts to build up pressure.


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Adjustment of Lever Reach


It should be a given that you can individually adjust the lever reach on your brakes. A solid brake which is well bled and which has a good heat management won’t need frequent adjustments – adjust once and stay happy with a constant pressure point.


In case of CLEG brakes, the lever reach can be adjusted by a 2 mm hex wrench which is easily accessible at the front of the brake lever.


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Adjustment of Pressure Point


See section “Adjustment of Free Stroke” above.


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Aging Brake Fluid


It is true for every hydraulic medium that its desired properties diminish with time – the fluid is aging. The decisive criterion for aging brake fluid is its water content. Clouding of the fluid caused by abrasion of the seals in the braking system, however, is more unpleasant than harmful. Unlike mineral oil, brake fluid based on polyglycol (DOT 3, DOT 4, and DOT 5.1) behave in a hygroscopic way, i.e. they are able to bind a certain amount of water chemically (putting it differently: “DOT pulls water”). This leads to a decrease of the fluid’s boiling point. When the water content reaches a certain level, the boiling point gets so low that the risk of the formation of steam bubbles and thus the occurrence of a sudden loss of brake power at high operating temperatures increases. That is why most car manufacturers state fixed intervals for the replacement of brake fluid. However, it is almost impossible to specify such intervals for bikes as the producers can’t assume that no work has been done on the brakes in between the theoretical maintenance intervals.


Brake fluid absorbs water from humidity mostly by getting into contact with air. Depending on how often the brake was “opened up” and on how carefully it was tightened, the level of water content can be higher or lower. If you want to play it safe, you should get the brake fluid replaced after two years at the latest. In contrast to cars or motorcycles, however, a bicycle’s system is completely closed during normal use so that nearly no water can diffuse into the brake fluid. By the way, there is a good reason for the use of brake fluid instead of mineral oil for the brakes of motor vehicles – see section “DOT Compared to Mineral Oil” below.


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Automatic Pad Adjustment


This is only relevant for disc brakes with reservoirs (which is the standard these days, so-called closed systems with manual adjustment have become rare). The nut for the piston seal (rectangular ring, also called “Quadring”) on the brake caliper has a special profile that ensures that the rubber seal follows the caliper piston movement when the brake is applied. If the brake is released, the Quadring – in interaction with the spring-loaded brake master cylinder - pulls the caliper pistons back into the piston bores by the same distance. Whenever the piston has to move further out of the piston bores than the Quadring can move along (because the brake pads or the disc rotor are too worn down, i.e. too thin), the caliper piston pushes through the Quadring – it readjusts. This technical trick ensures a constant clearance between brake pad surface and disc rotor (as a rule about 0.1 to 0.25mm/pad), no matter how worn the brake pads are.


By the way, you can’t re-adjust the pressure point (i.e. the clearance between brake pads and disc rotor) of brakes with automatic brake pad adjustment later as it’s defined by the profile of the nut in the brake caliper. If somebody tells the opposite, he’s wrong!


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Big Disc Rotor – High Braking Force!


Even the ancient Greeks understood the importance of the leverage ratio. The relevant leverage ratio for the function of a disc brake is the result of


-Mechanical ratio in the brake master cylinder
-Hydraulical ratio between BMC piston and caliper pistons surface
-Mechanical ratio between disc rotor size and wheel size

By re-equipping a disc rotor with a diameter of 160 mm to a diameter of 200 mm, the braking force of the same brake improves by about 25% for equal hand force. An increase from 180 mm to 200 mm improves braking force by about 11%.




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BMC Piston


This is the piston on the brake lever which transmits the brake lever’s mechanical force to the hydraulic system. The BMC (brake master cylinder) piston has two seals: the primary seal (mostly designed with a V profile) and the secondary seal (V- or O-ring). The primary seal builds up brake pressure (after closing the reservoir port), the secondary washer seals the system to the outside.


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Brake Pads – Organic or Sintered?


Organic brake pads are called organic because they mainly contain different hydrocarbon compounds, i.e. products of organic chemistry. The base (also called matrix) consists of synthetic resin and basically sticks the brake pad together. The fibers in the matrix are responsible for the lining’s mechanic strength. A brake pad’s performance properties, for instance its friction coefficient, are determined by the different fillers (e.g. metals) used. An organic lining can consist of up to 25 different materials.


Sintered brake pads are named after their production process. In a sintering process, different pulverized materials (usually metals or ceramics) are merged under high pressure and at a high temperature – the result is a material similar to metal. In general, sintered brake pads are harder and more wear-resistant than organic brake pads. However, sintered brake pads are more likely to squeal, put a strain on the brake calipers because of higher transmission of heat (which is why they are not compatible with some types of brakes), and their production is more expensive than that of organic brake pads.


In order to ensure optimal function, the disc rotors have to match the brake pads. The following applies as a general rule: Disc rotors with few, small perforations on the braking surface are suitable for the softer, organic brake pads, disc rotors with bigger perforations on the braking surface fit the hard, sintered brake pads (also see section “Glazing Brake Pads”). Hard pads match better with hard rotors. CLEG brakes work with both types of brake pads. By the way, it is quite easy to detect which kind of brake pads you have in front of you: Most carrier plates show one or several perforations. If the pad’s material fills the perforation, it probably is an organic brake pad. If the perforation is empty, it is a glued on sintered brake pad. (See picture on http://www.trickstuff.de/de/products/scheibenbremsbelaege.php).


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Caliper Piston


The pistons on the brake caliper are called caliper pistons. They press the brake pads to the disc rotor. The opposed piston on the brake master cylinder is called BMC piston; it causes the pressure in the system which presses the caliper pistons to the pads and the rotor. The piston diameter of two piston calipers nowadays is between 21 and 25mm. The piston diameter of four piston calipers nowadays is between 13 and 18mm.




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Contact Pressure


Tells us the force with which the brake pad is pressed to the disc rotor on each spot during braking. The design of the brake caliper is of good quality if contact pressure is as even as possible. You can check the design quality of your brake caliper by looking at the wear pattern of the brake pads. If the pads are worn down on one side only and askew, your brakes’ design is not ideal. The more regular the contact pressure, the more efficient the brake.


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Continuous Braking


Steep downhill passages that go on for miles (maybe even with additional baggage on the bike) are the worst case scenario for any kind of brake. In order to minimize the strain on the brake, you should stick to a few basic rules: Always apply both brakes at the same time. Misery loves company. If possible, shortly release the brakes so they can cool down a little and expanded brake fluid can flow into the reservoir. Don’t let the brake pads grind constantly. Instead, apply the brakes for a shorter period but with more force. If you notice a decrease of braking effect, you should pause for a few minutes for the brakes to get a short breather. Let go of the brakes as soon as you have come to a stand-still so that the heat from the disc rotor can’t move into the brake caliper!


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Degassing


Describes the effect of gas being released from the (organic) brake pads at very high temperatures, e.g. in case of continuous braking on long descents, mainly when the pads are quite new and the pads are still not bed in completely. This results in a poor coefficient of friction between brake pad and disc rotor – the braking effect is diminished (see section “Fading” below).


The term of degassing also is used when bleeding a brake system with new brake fluid: fill your syringe and suck extremely hard on the syringe piston before filling the brake fluid into the brake. You will be astonished how many micro-small gas bubbles will appear in the brake fluid. If you wish a really hard and defined pressure point you absolutely need to degass your brake fluid before you start bleeding.


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DOT


The American FMVSS 116 (Federal Motor Vehicle Safety Standard) establishes inspection requirements for brake fluid. According to the standard, you have to inspect the dry boiling point, the wet boiling point, as well as the viscosity (among others) in order to make a judgment about as brake fluid’s usefulness. Based on these criteria, the Department of Transportation (DOT) has established three groups: DOT 3, DOT 4, and DOT 5. The values for DOT 3 and 4 were designated for conventional brake fluid on the basis of polyglycol ether, the values for DOT 5 for brake fluid on the basis of silicon. Nowadays, there are conventional fluids that fulfill the DOT 5 values. For a while, these fluids were sold as DOT 4plus. These are called DOT 5.1 now. Be careful: DOT 5 is not compatible with DOT 5.1 or DOT 4, but it’s hardly obtainable in normal retail anymore anyway. To prevent mix ups, the fluids according to DOT 5 are colored blue, the conventional brake fluids on the basis of glycol ether (DOT 3, DOT 4, and DOT 5.1) are of a yellow-ish color.


Classification according to DOTDOT 3DOT 4DOT 5.1

Dry boiling point minimum (in °C)205230260

Wet boiling point minimum (in °C)140155180

Low-temperature viscosity (at -40 °C)                                   15001800900

Coloryellowyellowyellow


At Trickstuff, for special purposes we also use the racing brake fluid “Superformula” which is compatible and mixable with DOT 5.1 but has an even higher dry boiling point: 330°C. This is the highest boiling point available worldwide which makes “Superformula” the Formula-One brake fluid.


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DOT Compared to Mineral Oil


Both fluids have their advantages and disadvantages. The main advantage of mineral oil is the unproblematic maintenance. In contrast to DOT, mineral oil doesn’t harm your skin or the paint of your bike when getting into contact. The advantages of DOT are its ability to absorb water (!), its higher boiling point, the lower compressibility (hard pressure point!), the lower viscosity (DOT is runnier), and that you can use EPDM as seal material. In contrast to NBR or HNBR which are used with mineral oil, EPDM stands out because of constant properties and very long durability over a wider range of temperatures. DOT’s hygroscopic behavior, i.e. the property to bind water chemically, has advantages as well as disadvantages though. On the one hand, it causes the properties of DOT to worsen over time (see section “Aging Brake Fluid”). On the other hand, this property means that DOT binds water that might be absorbed into the braking system in course of carelessness during assembly or use. Not chemically bound water in the braking system would evaporate at a temperature of 100 °C. This in turn would result in a braking system failure (loss of pressure point). In our opinion, DOT certainly is the better medium for brakes under high demand.


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EPDM


This is an elastomer used for our piston seals on the brake caliper and for the reservoir’s membrane. It has a very wide range of temperatures at which it shows constant properties and shows very high durability (from – 40 °C to 120 °C). It perfectly harmonizes with DOT 4, DOT 5.1 and Superformula.


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Fading


Fading means that the friction coefficient between brake pad and disc rotor decreases whenever a certain temperature is exceeded. This causes the braking effect to decrease as well. The effect occurs because each type of brake pad has a temperature dependent friction coefficient (temperature coefficient). The friction coefficient increases from the cold friction coefficient up to the maximum friction coefficient at a certain temperature and then decreases again. The effect of a temperature dependent friction coefficient is intensified by the so-called degassing of the brake pads. In an extreme case, the fading effect can become so strong that an emergency stop becomes impossible even when using brute force.


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Fixed vs. Floating Brake Caliper


Nowadays all bicycle brake calipers are fixed type. The only floating caliper ever has been the legendary Magura Gustav M caliper.


In contrast to a floating brake caliper, a fixed brake caliper doesn’t change its position with regard to the disc rotor once it is installed. The convergence of the brake pads towards the disc rotor only occurs through movement of the pistons. That is why the caliper pistons of fixed brake calipers have to always be arranged in opposite pairs. Fixed brake calipers are available with 2, 4, or 6 pistons. A floating brake caliper can move sideways on a stator. This means you only have to include one (or several) caliper piston(s) on one side of the brake caliper. This then presses the brake pad to the disc rotor while simultaneously pulling the other brake pad to it.This “one-sidedness” is of advantage if there is no or only little space left on one side of the disc rotor which might be the case because a floating brake caliper is of very flat build on the side without caliper piston. One of the (often overstated) disadvantages of a floating brake caliper is its proneness to making scraping noises. In general, because of its design, or more precise its higher degrees of freedom, it is harder to optimize a floating brake caliper than a fixed caliper. For instance, it is extremely difficult to achieve even contact pressure of the brake pads.


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Front/Rear Distribution of Braking Force


60:40? 70:30? Or 80:20? This can be calculated quite easily for the roadside but when you use your bike on open terrain you can only get a rough estimate. This distribution can vary immensely - depending on type of terrain, sitting position, distribution of weight, and subsoil. In principle, however, the front wheel can transfer bigger braking forces than the rear wheel. That is why it makes sense to have a bigger disc rotor on the front wheel than on the rear. How strongly you apply the brakes in the front and the rear depends on the situation. You always should use both, though. Someone who only uses the rear brake to bike down a pass shouldn’t be surprised when the brake reaches its limit at some point.




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Glazing Brake Pads


The risk of glazing brake pads is especially high for new disc rotors and brake pads. As long as they aren’t run in, they produce excessive punctual heat during braking without correct lagging of the brake. This heat can result in the formation of a film as hard as glass with a very low friction coefficient on the brake pad’s surface. The effect of glazing is especially known from sintered brake pads. The surface of the softer organic brake pads is more easily ripped open because of the disc rotor’s perforation so that the formation of a closed film is impossible (organic brake pads that are soiled by oil, grease, or brake fluid are an exception. Glazing is possible in these cases). In order to prevent glazing, disc rotors of sintered brake pads have to have more aggressive perforation on the friction ring. It’s equally important to bed in new brake pads carefully. You should avoid longer descents (thus, continuous braking) during the first 30 to 50 kilometers after replacement of brake pads.


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Hot Spots


These are spots on the brake pad that heat up more than the rest of the pad. Hot Spots are usually caused by uneven contact pressure of a brake pad. The temperature is higher in spots where pressure is higher. The occurrence of Hot Spots leads to premature and uneven wear and tear of brake pads. Furthermore, it leads to higher risk of Fading because of punctual, high thermal strain on the brake pads. With brand new brake pads lots of micro-small hot spots occur because the surface of the pads and the rotor are not completely congruent which is one of the reasons for the poor brake power of new pads.


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Hygroscopic


See section “DOT vs. Mineral Oil” above.


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Hysteresis Curve


The hysteresis curve is determined on a brake dynamometer. If you have a little practice, you can read all of the brake’s important performance specifications off the hysteresis curve.


In order to determine the brake’s hysteresis curve, the brake lever is actuated with increasing force at constant speed (usually using a pneumatic cylinder) while the bike is placed on a roller dynamometer until it reaches a specified braking force (e.g. 600 Newton) that was defined beforehand. Then, the lever is slowly opened up again. During the braking process, you measure and save the values for manual strength and braking force (about 250 times per second). If you illustrate these values in form of a diagram, you get a closed curve with an ascending and a descending branch – your brake’s hysteresis curve. The values depicted on the ascending branch indicate the braking force that results from actuating the brake lever with certain force. The steeper the slope of the curve, the more the brake “bites” in practice. The shape of the descending branch tells us about the brake’s modulation. The closer the branches for the opening up and actuating of the brake are together, the better the modulation of the brake. The hysteresis curve of a V-Brake typically shows a more or less pronounced plateau in the upper part of the descending branch. This horizontal section reflects a consistently high braking force which occurs despite the force at the brake lever being decreased continually. In practice, this means that the brake opens up with a lag. The hysteresis curve of a hydraulic disc brake usually is very narrow – disc brakes are much more controllable. Reason for this is the lower friction within the force transmission in a hydraulic hose than in a mechanical cable.


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IS2000 vs. Postmount


The term “standard” suggests that people have reached an agreement about something which will then be enforced uniformly – it becomes the “standard”. For instance, there is the International Standard on disc brakes: IS2000. Great, one might think, this means the guys in the bicycle industry agreed on this so I can fit any kind of brake to any frame and any fork now. But that would be too easy, wouldn’t it? Cause in the meantime, the Postmount which originally was used by Manitou only caught up - even for the rear wheel. The Postmount Standard is vastly superior to the IS2000, especially when it comes to adjustability.


But there one thing that is not standardized: The Postmount sockets on the forks and rear triangles on your frames. You’ll find so called 6-inch sockets for 160mm rotors (despite the fact that 6 inches never equal 160mm), 7 inch sockets for 180mm rotors (despite…) and 8 inch sockets for 203mm rotors (the only one that makes sense). Most forks show 6 inch sockets, but unfortunately the sockets on the frames rear triangles tend to start a life of their own… - did anybody talk about “standard”?


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Modulation


Power is nothing without control. This slogan has become quite stale. Besides, it is pinched from an ad for tires! But it nevertheless is true. The more technical the trails get and the closer you get to the limit during your bike rides, the more important the controllability of the brakes. It is important that a brake carries out the orders the biker issues by applying the brake levers exactly. This means as genuine as possible, 1:1. The one second a badly controllable brake may need to unblock the blocked front wheel could turn out to be very hurtful. You can find instructions on how to improve the modulation of a brake in the sections “2 Pistons vs. 4 Pistons” and “Pressure Point”. We’re so bold to claim that our “CLEG” is one of the most controllable brakes there is. Feel free to do a test ride and we’re pretty sure you will be convinced!


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One-Piece Brake Caliper


By forging a one piece caliper not instead of connectin a right and left caliper half by using steel or titanium bolts (yoke connection bolts) you can reduce the monobloc brake caliper’s weight by a few grams. On top of that, the brake caliper becomes smaller and more compact, as there is no need to leave space for the screw connection. Whether the one-piece construction has further advantages remains an open question though. Every producer of brake calipers will give a different answer to this question, depending on whether they produce one-piece constructions or not. In general, however, one-piece brake calipers are not stiffer than others. On the contrary, the preload caused by the yoke connection bolts (if their position is correct) leads to stiffness of the bolted brake calipers and prevents them from expanding when the brake lever is actuated.


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Open vs. Closed System


Nowadays, most hydraulic disc brakes on the market have a so-called open system. It is called “open” because the hydraulic system is open, i.e. not pressure-tight, when the brake lever is not actuated. The opening is inside the brake master cylinder and connects he high pressure cylinder and reservoir when the piston is in its rest position. However, there is no opening towards the atmosphere as there is on the brakes of cars or motorcycles. Brake fluid can move into or out of the reservoir (low-pressure region) into the braking system (high-pressure region) through one (or several) bore holes. This connection port is closed whenever the brake lever is actuated so that the pressure which is necessary for braking can build up. The open system enables automatic brake pad adjustment and prevents the brake from shutting down in case of severe heating.


In contrast, the hydraulic system of a closed system (e.g. Hope C2, which is not up-to-date anymore, and a unique newcomer from German production) is pressure-tight all the time. Automatic adjustment doesn’t take place. You would have to adjust the pressure point manually. However, you also have to balance out the brake pads’ wear and tear manually and there is a risk of the brake shutting down because of overheating.


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Overheating


When the brake is applied, the friction at the disc rotor converts the kinetic energy of biker and bike into heat. This process can produce temperatures of up to 500 °C between brake pad and disc rotor. Thus, heat is always produced. However, the resulting heat should neither overheat the disc rotor or the brake pad nor should it heat up the brake caliper with the brake fluid and its piston seals by too much. If disc rotor and brake pad get too hot, the braking effect might decrease by too much (see sections “Degassing”, “Fading”). If the brake caliper overheats, steam bubbles may form in the brake fluid (loss of pressure point!) or the rubber seals may get brittle. In order to guarantee optimal function of the braking system, this thermal energy has to be led away from the friction spot on the brake pad and distributed in a way that the permitted temperatures are not exceeded in any component. The biggest share of heat is emitted to the air through the disc rotor. The bigger and more solid the disc rotor, the higher its thermal capacity – this means it can absorb more thermal energy before reaching its thermic equilibrium. Therefore, assembling a bigger disc rotor usually solves the problem of overheating. By the way, the crucial element of the rotor is its friction ring. The steel used for disc rotors of bicycles is relatively bad in conducting heat so that the heat is not distributed over the whole disc. The disc rotor’s spokes heat up only slightly during braking. The disc rotor is cooled down constantly by surrounding airflow. Without this airflow, the disc brake overheats in no time. The higher the air temperature, the lower the cooling effect and the higher the risk of exceeding the critical temperature. Exactly how much heat is transmitted from brake pad into brake caliper or how much is absorbed by the disc rotor depends on the brake pad. Given the same braking process (=equal heat production), organic brake pads transmit less heat into the brake caliper than sintered (see section “Brake Pads – Organic or Sintered?”). This goes easy on the brakes and the brake fluid, but puts a strain on the disc rotor.


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Piston Diameter


The piston surface ratio of BMC piston to caliper piston determines a hydraulic system’s transmission ratio (see section “Transmission Ratio”). In addition, in case of a 4-piston fixed brake caliper you can achieve even contact pressure of brake pads by using different piston diameters.


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Pressure Point


Is there a trade-off between high braking power and hard pressure point? The higher the transmission ratio of a brake, the softer a brake feels. Brakes with a relatively low transmission ratio, in contrast, usually have a pleasantly hard pressure point – but they don’t work quite as well. Of course the hardness of the pressure point also depends on the brakes’ design and on the quality of the brake hose. Four-piston brakes always are harder than two-piston brakes with the piston surfaces being equal. Steel braided brake hoses are harder than conventional hoses. In opposition to the generalized opinion the production method of the brake caliper (whether it’s a one-piece or two-piece) doesn’t have a fundamental influence on the hardness of the pressure point.


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Quadring


The sealings inside the brake caliper are called “Quadring” or “rectangular ring”. Their cross section is square or rectangular (in contrast to the usual O-rings). Depending on the type of brake fluid used, the Quadrings consist of different elastomers. In case of mineral oil, they mainly consist of NBR or HNBR, in case of DOT, mainly EPDM is used.


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Reservoir


This applies to self-adjusting disc brakes. The reservoir is linked with the master cylinder by one or several boreholes, the reservoir port.When releasing the brake lever, brake fluid might flow through the port into or out of the reservoir. If the brake lever is actuated, the connection between the reservoir and the rest of the braking system is interrupted. Thus, no pressure builds up in the reservoir during braking.The actual balancing takes place in two ways: First, when the caliper pistons on the brake caliper re-adjust (see “Automatic Brake Pad Adjustment”) and brake fluid flows from the reservoir into the high-pressure system. Second, when brake fluid heats up and expands inside of the brake caliper. The expanded volume of the hot fluid is absorbed by the reservoir. Requirement: You shortly have to let go of the brake lever for the reservoir port to be open. This prevents the brakes from shutting down. The reservoir is always sealed by a membrane that needs to adjust to the brake fluid’s changing volume inside of the reservoir.


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Slip-Stick Effekt


The change from static friction to gliding friction between brake pad and disc rotor results in an inconsistent friction coefficient between brake pad and disc rotor during braking. This jolting fluctuation of the friction coefficient is the cause for squealing brakes.


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Torx


So-called torx screws have gained acceptance for attaching the disc rotors to hubs with a 6-hole mounting. They have very flat heads and their multiple gearing is able to transmit higher torques than conventional hexagon bolt heads. Spinning is almost impossible in case of torx screws made of steel. The torx screw sizes M5x12 and Tx25 are regarded the standard for attachment of disc rotors.


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Transmission Ratio


If you had to press the brake pads to the disc rotors manually, you would not achieve a perceivable braking effect. In practice, however, it often only takes one finger at the brake lever to achieve full braking. This means the relatively small strength of your finger is multiplied within the braking system before it reaches the brake pads. The force of this effect depends on the brake’s transmission ratio. The total transmission ratio is composed of a mechanical part (which is determined by the ratios at the brake lever plus the ratio between wheel diameter and rotor diameter) and a hydraulic part (depending on the piston surface ratio of BMC piston to caliper piston). The higher the transmission ratio is, the higher the braking force at given hand force. However, the transmission can’t be increased indefinitely because this also increases the lever stroke and softens the pressure point.


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Yoke Connection Bolt


Yoke connection bolts connect the two halves of a brake caliper (except for in case of one-piece brake calipers). A brake caliper’s preload which is caused by the bolts ensures that the brake caliper hardly expands when exposed to piston forces. Steel bolts are about 40 percent stronger than titanium bolts of the same dimensions. If you wanted to design your titanium bolts to be as strong as steel bolts they’d weigh in as much as steel bolts.


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Trouble?


Most problems that occur during normal use require only little effort to be fixed. You don’t necessarily have to take your bike to a mechanic. If a problem occurs, please read our FAQ section thoroughly. In that section we answer your most frequently asked questions and give instructions on how to solve smaller problems in an instant.


Of course we are also willing to answer your questions via our hotline or e-mail.

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