Bicycle Disk Brakes

Somewhat outdated. Written in 2008.

For those struggling with their decision for or against disk brakes I will collect some information from my experience with several types of popular and wide spread systems. Also, I will describe installing a Shimano 2008 disk brake system to my big dummy.

Always keep in mind: losing brake power is severe and may cause heavy injury, damage or death. Under no circumstances perform any modifications or maintenance when not absolutely sure about it. Check back with bicycle professionals or simply have your shop do it, take maximum care about everything concerning your brakes and never use any information from this page if you are not totally sure about it.
As stated here, this blog is non professional information and no responsibility is taken for correctness or whatever. When in doubt, please do not use this information at all.

Argueing about Disk Brakes

Benefits

  • Strong and reliable braking power under any circumstances as like rain, snow, dirt.
  • No interference of cable routing with brake alignment (as like V-brakes). Probably an issue with lots of baggage on cycle
  • Less exposure to dirt and mud compared to rim brakes (drum brakes are even better)
  • Use nice (colorful) rims without wearing them off
  • Easy wheel changing without a need to realign caliper. Quick and easy mounting and dismounting wheels especially with fat tires.
  • Small spare brake pads when touring
  • No need for ordinary brake bosses, looks nice
  • No danger of brake wire disruption
  • No adjustment 3D puzzle as like hydraulic rim brakes
  • lightweighted compared to drum brakes
  • Easy cleaning, no rims rubbing required

Downside

  • Weight, compared to rim brakes
  • Compared to drum brakes, there is some exposure to dirt
  • Depending on riding conditions brake pads may wear off quickly. However, there is no rim wear at all. Also, manufacturers mostly offer different types of brake pads providing a different tradeoff between performance and durability
  • Need for stronger wheels and spoke patterns, no radial patterns (anyway, this is not an issue with cargo bicycles)
  • Need to upgrade typical cyclists knowledge about brake technology to be able to perform maintenance and service
  • Performance and noise issues may be related to frame quality, which cannot be modified in case of problems
  • Initial installation and adjustment may become picky and delicate, depending on frame quality, disk sizes, adapters used
  • Bicycle should not be turned upside down if possible, at least levers must never be pulled when cycle is positioned on its handle bar (applies to hydraulic disk brakes with compensation reservoir only).
  • Needs a few small special parts, some syringe and some piece of hose for maintenance, shortening, bleeding
  • Maybe there is braking noise when wet or dirty, but this may apply to rim brake systems as well. Also this strongly depends on frame details, rotors and type of brake pads used.
  • Rotors may be subject to damage when being hit hard.
  • May put restrictions on handlebar choice
  • Important quick release issue: a big issue with disk brakes and quick release axles was pointed out by Vik recently and I would like to mention it here. With usual fork construction and caliper mount sockets brake actuation generates a strong force trying to dislocate the wheels axle direction downwards in the dropouts. In case of loosened quick release axle and/or in case of missing dropout protection guards this might cause serious crashing due to losing front wheel for instance. Might be an issue wih rear wheel as well, depending on layout. Keep in mind and tighten wheels, or if possible use fixed axle systems. Also, there are some forks around fixing this issue with caliper mounts turned forward, as like Cotic Roadhog fork, for instance.
  • Some hydraulic systems may be functionally affected by cold environment, esp. when riding in winter. This is a matter of brake piston seals losing some of their flexibility, also viscosity of brake fluid (systems with mineral oil mostly)

Conclusion

In my opinion this is very much a matter of getting used to this technology and keeping in stock some special parts and tools just in case of maintenance, to obtain a low maintenance system with good and reliable power, perfectly suitable for cargo cycles and all day usage. Once installed properly (which may require some experience) it massively reduces the effort for fiddling around with brakes, wheels installation, wheels change. So, for all my multi purpose all weather bicycles these are the brakes of choice. For special types of bicycles mechanical disk brakes driven by wire (vs. hydraulic systems) may be a good choice, especially folding bikes for instance.

There may be additional considerations for extreme ways of using bicycles as like travelling the world or riding at very uncommon conditions or regions. I do not want to cover such things due to lack of experience.

Hydraulic vs. mechanical systems

While hydraulic systems are a bit more complicated to install and need bleeding when shortening brake hose at installation, they are quite unaffected by dirt due to closed and sealed off technique. Mechanical systems are easier to install with ordinary tools available everywhere, but caliper leverage and brake wire may be exposed to dirt. There is no problem with positioning bicycle upside down with mechanical systems and there is no need to bleed system, also brake wires are available at any length needed. For some hydraulic systems availablity for long brake hose is limited, so one needs to check for replacement hose (see brake hose section below). For those who like to use dropbars or whatever special handlebars, there are no hydraulic brake levers available, so one might have to stick to some mechanical brake system and use brake levers of choice.
Most likely there is some difference in braking performance between both types of brake systems. On the other side, mechanical systems are not affected when riding under cold conditions (see next section).

Brake Fluids, Brake Piston

Considering hydraulic disk brakes, there are systems with mineral oil filled in and such with DOT brake fluid as like used in motorcycles and cars. While the former is maintenance free since there is no need to replace it, the latter can take more heat without boiling but needs to be replaced every 2 years due to its hygroscopic nature.

Magura offers mineral oil which is neutral to environment and safe to use regarding health. DOT brake fluid must be handled with care, may spoil other surfaces and should be dumped at hazardous waste sites. Mineral oil used to be good enough for my braking usage in all cases, so I have always been using such systems with respect to easier maintenance.

Note that when riding under very cold conditions, using DOT brake fluid system might offer better operation since viscosity of mineral oil may be decreased considerably. I know about issues with current Shimano systems and probably a few Magura systems, but the latter do not seem to be affected so much. Most likely, this may be a matter of brake piston rubber seals getting cold and becoming harder and thus no longer being able to retract brake pistons when brake levers are released. This means, brake actuation will begin immediately after pulling levers only a very small distance (creates a hard brake point at brake levers), or probably there may be a nasty continuous grind of brake pads at rotors.

Brake hose

For a big dummy rear brake system, brake hose in length 1.9m approximately is required, depending on frame size, handlebar used, cable routing. Take care to supply enough to let handle bar flip around without tensioning cable, just in case. However, since unnecessary wide cable loops might increase risk of disruption, do not feed in too much of it.

Magura offers brake hose in length up to 2.5m, which is enough by far. Take care to use the right type of liner, since Magura has got low pressure systems (Julie, HS rim brakes) and high pressure systems as like Luise, Marta. Take care to use high pressure brake liner for the latter types of brakes. Never use HS brake liner for disk brake systems. Magura brake hose has got a fixed end to be used at caliper side and an open end that may be cut in length, which has to be installed at lever unit. Cutting off the fixed end will make brake hose unusable for Magura systems, but you can still use it with Shimano systems since Shimano does not need a fixed end for its brake hose.

Shimano offers brake hose in length up to 1.7m, which is too short for big dummy rear brake. So, when using a Shimano rear disk brake system, some replacement braking hose is needed. It can be done in several ways. Either one could use Magura (pressure proof) brake hose with Shimano connectors, olives, hex nuts, or one could get specially tailored parts or aftermarket brake hose. Here are some distributors for all systems all length hydraulic brake hoses:

Please note that intermixing different vendors parts on your brakes may cause loss of warranty or whatever, according to brake manufacturer.

Brake levers (radial vs. conventional pump)

There are conventional and radial brake pumps. Radial pumps are smart design since not using much space at handle bar. For instance, former Shimano brake levers used up the complete space available at handle bar, and cabling got quite a bit messy. I would recommend radial pumps as like used by Magura mostly, some Hayes systems, some Shimano and maybe others. On the other hand, there are systems with interchangable brake pumps as like some Avid or Hayes Strokertrail (radial pump) and maybe others. It looks like a good idea being able to simply swap left and right brake lever units. This also makes sense when maintaining several bicycles, in case there is a need of rotating parts between them. This way, lever units can be used both for front and rear brakes without restrictions.

Rotors

Currently I know of 6 bolt mounted rotors, 4 bolt mounted rotors as like Rohloff and centerlock rotors. In my opinion, centerlock hubs and rotors are a good choice due to easy exchange. On the other hand, for long trips without big toolkit, 6 bolt rotors might be a better choice, since these can be exchanged everywhere by use of some small torx allen key, while centerlock hubs need a special tool for installing Shimano cassettes. On the other hand, centerlock may be quite indestructible, while small bolts could easily be overturned and threads/hubs will be damaged this way. 6 bolt rotors can easily be installed to centerlock hubs by use of centerlock adapters available from Shimano, DT Swiss and others. Centerlock rotors can only be installed at centerlock hubs.

For the big dummy, 180mm rotors seem to be a good choice, at least for me, and my brakes operate without noise, even when wet! Note that at the big dummy it is perfectly alright to use equally sized rotors at front and rear due to long wheelstand. Rear brake can (and should) take an noteworthy percentage of total braking performance. The big dummy is unlikely to overturn and there may be load on rear wheel even when braking. Manufacturer Surly even strictly advises against using front brake only, since fork may be damaged when braking hard with load on the back.

Spoke pattern

Ordinary pattern with 3 or 4 crossings should be ok, depending on hub and wheel size. With big hubs and smaller (or V-shaped) rims you may consider 2x crossings of spokes. No 1x or radial patterns. Shimano advises about guiding and trailing spokes. Basically, for disk brake wheels you can perfectly stick to Sheldon Browns wheelbuilding page at the front wheel, but would probably (just to be perfect) swap guiding and trailing spokes at drive train side of rear wheel, as like documented in Shimanos disk brake documentation.
Reason is, that guiding spokes are stressed when braking, while trailing spokes tension will be released a bit (spoke compression). As a consequence, it is a good idea to make sure, guiding spokes are running underneath trailing spokes at outer crossing, since this way they will maintain better tension on the latter ones when braking hard. At drive train side of rear wheel, Shimano keeps it the other way, so trailing spokes are running inside at outer crossing and will put a bit of tension on guiding spokes when pedaling hard. So, rear wheel somehow has got asymmetric spoke patterns at left vs right side.

When building your own wheels, this means, at front wheel you can stick to Sheldon Browns wheelbuilding compendium, starting with trailing spokes at both sides of wheel, inserting them from outer side such that they are running inside hub flange. At rear wheel, on drive train side, you will have to insert trailing spokes from inner side of hub flange. This causes a bit of mess when inserting guiding spokes later on, but will fulfil Shimanos spoke pattern specs for disk brakes.

Take care to use quality spokes for big dummy wheels, no matter whether using disk brakes or not. I may recommend lightweighted but strong Sapim Force (2.2/1.8/2.0) or DT Swiss Alpine III (2.34/1.8/2.0) in combination with brass nipples. For hubs with big spoke holes, I suggest inserting little brass shims at spoke heads before inserting spoke into hub, to improve spoke heads seating in spoke hole and reduce movement of spoke heads in case of extreme impacts hitting the wheel. Build wheels with stiff rims and high spoke tension and check spoke tension every now and then. This way it should be possible to avoid wheel outage for a long time, hopefully along the whole bicycles life (at least with disk or drum brakes since rims are not wearing off).

Installation of Shimano XT 2008 disk brakes at big dummy

  1. Take care to protect rear left freeloaders nylon mesh from brake caliper. Caliper gets very hot and might damage freeloader bag otherwise. Xtracycle offers some protective clamp for caliper. I am currently just using some layers of tape where freeloader touches brake caliper.
  2. Check for availability of lengthy rear brake hose. 190cm may be a good start, depending on frame size, stem geometry and handle bar size.
  3. Want very soft pressure point and soft lever pull as like I do? Or the other way round? Choose disk brake model accordingly.
  4. Postmount calipers may be a good idea as these allow for better adjustment.
  5. For installation obtain bleeding kit, enough brake hose fitting front and rear brake with fittings and installation kit, small alignment washers for IS2000 caliper adjustment or postmount radial alignment and keep to manufacturers installation guide. There is nothing special about brake installation at Big Dummy apart from getting long rear brake hose and -as always- find a way for smooth and safe cable routing.
  6. At first, check for perfect wheel installation and alignment, also perfect seating of quick release axles or whatever. Initial brake adjustment: in my opinion, visual alignment of calipers is necessary. As a first step, it may be a good start to losen postmount bolts, pull brake lever and tighten bolts. However, in most cases this does not give a good inital caliper alignment. After some test riding with brakes applied, realign calipers by checking perfect alignment of disk rotor within caliper. With some brake types caliper alignment of front brake can be controlled while riding at bright daylight and looking at disk running within front caliper. For non postmount systems, caliper needs to be aligned by use of small washers or probably by carefully removing some paint at the forks caliper mount.

Schreibe einen Kommentar

Deine E-Mail-Adresse wird nicht veröffentlicht. Erforderliche Felder sind mit * markiert.