Whats the difference in brakes: Cantilever vs Disc brakes: Advantages of Disc brakes vs Cantilever brakes: More braking power - Hydraulic brakes even more. Moderate rim damage does not affect braking. Not affected by rain or snow and mud. Pads last longer and are easy to replace. Brakes don’t go out of true. Less prone to fading on long down hills. You can make the bicycle rims lighter weigh so less rotational weight. You can build a wheel with super wide rims and huge tires. Great if you want the ability to put bigger tires and flexibility with fenders on road bicycles. Disadvantages: Heavier then cantilever. More expensive. Require specific hubs and disc brake mounting tabs on rear wheel and fork. Sometimes squeak - Oil on the discs can make this occur. Can be hard to set up initially. Discs are vulnerable to bending when transporting the wheels separately from bicycle. Disc brakes can interfere with Pannier racks and bags. Some bicycle designs can be dangerous with front wheels coming off the forks. Advantages and disadvantages[edit] See also: Actuation mechanisms Disc brakes tend to perform equally well in all conditions including water, mud, and snow due to several factors: The braking surface is farther from the ground and possible contaminants like mud which can coat or freeze on the rim and pads. With rim brakes, the first point that mud builds up on a mountain bike ridden in thick mud is usually the brakes. A mountain bicycle with disc brakes is less susceptible to mud buildup provided the rear frame and front fork yoke have sufficient clearance from the wheels. Disc brakes are less prone to fading under heavy or prolonged braking compared with rim brakes, and the heat is not dissipated into the tyre. There are holes in the rotor, providing a path for water and debris to get out from under the pads. Wheel rims tend to be made of lightweight metal. Brake discs and pads are harder and can accept higher maximum loads. Disc brakes do not create wear on the rim unlike rim brakes, especially if grit becomes embedded in the brake pads. It is possible to ride a bicycle with a buckled wheel if it has disk brakes, where it would not be possible with a rim brake because the buckled wheel would bind on the brake pads. The use of very wide tyres favours disc brakes, as rim brakes require ever-longer arms to clear the wider tyre. Longer arms tend to flex more, degrading braking. Disc brakes are unaffected by tyre width. Unlike some rim brake designs, disc brakes are compatible with front and rear suspension. Disc brake assemblies are heavier than rim brakes, and are generally more expensive. Disc brakes require a hub built to accept the disc. Front hubs designed for discs often move the left hubs flange inward to make room for the disc, which causes the wheel to be dished. A dished wheel is laterally weaker when forced to the non-disc side. Other hubs use conventional flange spacing and provide a wheel without dish, but require a less common wide-spaced fork. A rim brake works directly on the rim and the attached tyre; a disc brake applies a potentially large torque moment at the hub. The latter has two main disadvantages: The torque moment must be transmitted to the tyre through the wheel components: flanges, spokes, nipples, and rim spoke bed. Engineering for this moment inevitably leads to a heavier wheel. A front disc brake places a bending moment on the fork between the caliper anchor points and the tip of the dropout. In order to counter this moment and to support the anchor points and weight of the caliper, the fork must be thicker and heavier.[28] The heavier fork and wheels compound the weight disadvantage of the brake assembly itself. Disc brakes are sensitive to lateral play or slop, so careful manufacture and adjustment is required. Hub bearing wear is an issue with disc brakes.[citation needed] While all types of brakes will eventually wear out the braking surface, a brake disc is easier and cheaper to replace than a wheel rim or drum. Heat build-up can lead to failure with disc brakes. Disc brakes heat discs in the same way as rim brakes heat rims, but discs provide an inherently smaller surface to dissipate heat. Excessive heat leads to boiling hydraulic fluid, resulting in brake fade or total failure. Overheating is more common in road cycling due to longer steeper descents, higher speeds, and fewer opportunities to release brakes and cool pads and discs than is typical in mountain biking.[29] If brake friction exceeds convection and radiation losses, the temperature of the disc can quickly rise to where the metal weakens, causing the disc to warp or crack.[citation needed] The design and positioning of disc brakes can interfere with pannier racks not designed for them. For this reason, many manufacturers produce disc and non-disc versions. Since about 2003, riders have reported a dangerous problem using disc brakes: under hard braking, the front wheel comes out from the dropouts. The problem occurs where the brake pads and dropouts are aligned so the brake reaction force tends to eject the wheel from the dropout. Under repeated hard braking, the axle moves in the dropout in a way that unscrews the quick release. Riders should make sure the skewers are properly tightened before riding.[30][31] Forks that use different brake/dropout orientations or through-axles are not subject to this problem. Hydraulic vs. mechanical[edit] There are two main types of disc brake: mechanical (cable-actuated) and hydraulic. For more details on this topic, see Actuation mechanisms. The advantages of cable-actuated disc brakes are in their lower cost, lower maintenance, and lighter system weight. Cable-actuated disc brakes also have another potential advantage: they are traditionally the only type of disc brake that can be used with the brake levers found on drop handlebars[32] however drop bar hydraulic conversion components have been developed.[33][34] Mineral Oil vs. DOT 4/5.1 Fluid[edit] Hydraulic disc brakes make use of two common forms of fluid. Automotive grade DOT 4 or DOT 5.1 which are hygroscopic and has a boiling point of 230 °C, and mineral oil which is not hygroscopic and has varying boiling points depending on the type of mineral oil.[35] O-rings and seals inside the brake are specifically designed to work with one or the other fluid. Using the incorrect fluid type will cause the seals to fail resulting in a squishy feeling in the lever, and the caliper pistons are unable to retract, so a scraping disc is common. To ensure the correct fluid is used the manufacturer will usually stamp or laser mark the lever reservoir cap/body with the compatible fluid type.[citation needed] Single vs. dual actuation[edit] Many disc brakes have their pads actuated from both sides of the caliper, while some have only one pad that moves. Dual actuation can move both pads relative to the caliper, or can move one pad relative to the caliper, then move the caliper and other pad relative to the rotor, called a floating caliper design. Single-actuation brakes use either a multi-part rotor that floats axially on the hub, or bend the rotor sideways as needed. Bending the rotor is theoretically inferior, but in practice gives good service, even under high-force braking with a hot disc, and can also yield more progressiveness (which is generally sought after for the rear brake).[citation needed] Self-adjusting[edit] Many hydraulic disc brakes have a self-adjusting mechanism so as the brake pad wears, the pistons keep the distance from the pad to the disc consistent to maintain the same brake lever throw. Some hydraulic brakes, especially older ones, and most mechanical discs have manual controls to adjust the pad-to-rotor gap. Typically, several pad adjustments are needed during the life of the pads. Multi-part construction[edit] Hydraulic calipers are typically made in one piece to reduce weight, increase stiffness and reduce leaks. The two-piece design reduces heat build-up more effectively.[citation needed] Many older brakes and high-performance models use a two-piece caliper, where the two parts are bolted together. Many mechanical disc brake calipers are two-piece, for example, Avid BB-5 and BB-7 brakes. Multiple pistons[edit] Many high-performance calipers use two or three pistons per side; lower-cost and lower-performance calipers often have only one per side. Using more pistons allows a larger piston area and thus increased leverage with a given master cylinder. Also, pistons may be of several sizes so pad force can be controlled across the face of the pad, especially when the pad is long and narrow. A long narrow pad may be desired to increase pad area and thus reduce the frequency of pad changes. In contrast, using a single large piston may be heavier to accomplish the same results. Caliper mounting standards[edit] There are many standards for mounting disc brake calipers. I.S. (International Standard) is different for 160mm and 203mm rotor and differs between forks with a QR and 20 mm through axle. The post-mount standard also differs by disc size and axle type. Many incompatible variants were produced over the years, mostly by fork manufacturers.[citation needed] The mount used on the Rockshox Boxxer is the most typical of these specialty mounts, but most fork manufactures now use either the IS or post-mount standard for their current forks. As a point of reference, Hayes currently sells no fewer than 13 different adapters to fit their brakes to various mounting patterns.[36] Advantages and disadvantages of various types of mounts[edit] A disadvantage of post mounts is that the bolt is threaded directly into the fork lowers. If the threading is stripped or if the bolt is stuck, then the threads will need to be repaired, or the seized bolt drilled out. Frame manufacturers have standardized the IS mount for the rear disc brake mount. In recent years post mount has gained ground and is becoming the most common. This is mostly due to decreased manufacturing and part cost for the brake calipers when using post mount.[citation needed] A limitation of the mount is that the location of the rotor disc is more tightly constrained: it is possible to encounter incompatible hub/fork combinations, where the rotor is out of range. With an IS mount, the caliper can be moved closer to or further from the mount point using spacers; this can permit a wider range.[citation needed] Disc mounting standards[edit] There are many options for disc rotor mounting - International Standard (IS), centerlock, Cannondales 4-bolt pattern, Hopes 5-bolt pattern and Rohloffs 4-bolt pattern, to name a few. IS is a six-bolt mount and is the industry standard. Centerlock is patented by Shimano and uses a splined interface along with a lockring to secure the disc. The advantages of centerlock are that the splined interface is theoretically stiffer, and removing the disc is quicker because it only requires one lockring to be removed. Some of the disadvantages are that the design is patented requiring a licensing fee from Shimano. A Shimano cassette lockring tool (or an external BB tool in case of through-axle hub) is needed to remove the rotor and is more expensive and less common than a Torx key. Advantages of IS six-bolt are that there are more choices when it comes to hubs and rotors. IS rotors use button head socket cap screws (typically M5x0.8x10mm with locking patch) with either a hex socket or Torx socket to secure them to the hub. This can make IS rotors more time consuming to install and remove. Torx screws are preferred for the superior torque: it is easy to strip the socket of a hex bolt by overtightening it, leaving a rotor that is hard to remove.[citation needed] Standards[edit] Centerlock (Shimano proprietary) International Standard (IS) (in widespread use) 44mm BCD AMP 6-bolt (AMP proprietary, obsolete) Cannondales 4-bolt pattern (obsolete) Freewheel thread (used by Mountain Cycles and others; obsolete) Hope Technologys 5-bolt pattern (Hope proprietary, obsolete) Hope Technologys 3-bolt pattern (Hope proprietary) Rohloffs 4-bolt pattern (proprietary, 65mm, same as some chainrings) Rock Shox 3-bolt pattern (proprietary, obsolete) Disc sizes[edit] Disc brake rotors come in many different sizes, typically 160 millimeter, 185 mm, or 203 mm in diameter. However, many other sizes are available as brake manufacturers make discs specific to their calipers — the dimensions often vary by a few millimeters. Larger rotors provide greater braking force for a given pad pressure, by virtue of a longer moment arm for the caliper to act on. Smaller rotors provide less stopping power but also less weight and better protection from knocks. Larger rotors dissipate heat more quickly and have a larger amount of mass to absorb heat, reducing brake fade or failure. Downhill racers typically run larger brakes to handle the greater braking loads and extended braking duration. Cross country racers typically run smaller rotors which can handle smaller braking loads yet offer a considerable weight savings of as much as 100g per rotor.[37] It is also common to use a larger diameter rotor on the front wheel and a smaller rotor on the rear wheel since the front wheel does the most braking (up to 90% of the total).[38] With large rotors to dissipate heat, disc brakes are becoming more popular as drag brakes.
Posted on: Thu, 30 Oct 2014 13:34:25 +0000
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