In this article, we answer the following questions:
- What are the advantages and disadvantages of disc brakes?
- Can I retrofit my bike with disc brakes?
- What different brake calliper mounts are there on the frame & fork?
- What are adapters for & why are there brake discs in different sizes?
- Are mechanical or hydraulic disc brakes better?
- Are all brake fluids the same for hydraulic brakes?
- What happens if you accidentally bleed a mineral oil system with DOT or vice versa?
- Which wheels are suitable for disc brakes?
- What is the difference between hubs with IS2000 mount & Centrelock? What about Rohloff & Pinion?
- Can 6-hole discs also be mounted on Centerlock hubs?
- Why shouldn't you touch brake discs directly after a ride?
- Why are some brake discs one-piece and others fitted with a separate carrier?
- Are the braking surfaces of the discs always made of solid steel?
- What are the pros & cons of Shimano's "IceTech" & "Freeza"?
- Can I use brake discs from other manufacturers?
- What is the difference between metallic & organic coatings?
- Do disc brakes need to be braked?
- Why do my disc brakes squeal even though I have run them in?
- How do I avoid transport damage?
- How often do disc brakes need to be serviced?
1. what are the advantages & disadvantages of disc brakes?
Advantages
- Due to their higher surface pressure, disc brakes have better braking performance in the wet.
- You need up to 20% less manual force to achieve the same braking power - an advantage not only for women and older people.
- The rims no longer wear out.
- With a "figure of eight", the rims no longer grind on the brakes.
- The rims can no longer overheat on long descents in the mountains.
- The brake discs do not get dirty so quickly.
- As a rule, brake pads for disc brakes last longer than pads for rim brakes.
- They are more suitable for very thick tyres.
Disadvantages
- Disc brakes are heavier than rim brakes and are usually more technically complex.
- They cost more than rim brakes, especially if they are hydraulic disc brakes.
- Instead of the rims, the brake discs can now overheat on heavily loaded tours or long descents.
- Disc brakes can easily be damaged during bike transport.
- Hubs and spokes are subjected to greater stress.
- Disc brakes have to be braked, which is not always easy for the layman.
2. can I retrofit my bike with disc brakes?
This is only possible if the fork and/or the frame have the appropriate mounts for disc brakes. These are two mounting points near the left dropout. If you really want to, you can replace your rigid or suspension fork with a fork designed for disc brakes. However, if the frame has no mounts, you cannot fit disc brakes at the rear. Wheels must be disc-compatible.
3. what different brake calliper mounts are available on the frame & fork?
There are currently two standards: Postmount and IS2000 (International Standard). With Postmount, the mounting points are 74.2 mm apart and are aligned along the longitudinal axis.
On the IS2000, the mounting holes are 51 mm apart and at right angles to the direction of travel. The mounts are usually fitted in such a way that brake discs with a diameter of 160 mm can be fitted as standard at the front and rear. This also means that discs smaller than 160 mm cannot be fitted.
However, there are more and more mountain bikes with direct post mounts; they accept 180 mm discs as standard. As the trend is clearly moving towards larger brake discs, this arrangement may also become established on trekking bikes at some point.
4. what are adapters for & why are there brake discs in different sizes?
There are countless different adapters for IS2000 and Postmount. They all serve one purpose: they move the brake calliper into the right position for the corresponding disc size. This makes it possible to fit larger discs. These are available in many different sizes. If in doubt, you should always choose the larger disc. It enables higher braking performance, weighs a little more and puts more strain on the frame and fork. Not every fork can accommodate brake discs larger than 180 mm.
Some cross and road bikes use 140 mm discs, while trekking bikes start at 160 mm. If you either weigh a little more or are travelling with a lot of luggage, you are well advised to use 180 mm discs. If you're travelling in the Alps, you'll probably prefer 203 mm discs. Discs with 220, 240 or even 254 mm diameter (Santana) are often fitted to tandems and transport bikes.
5. are mechanical or hydraulic disc brakes better?
Similar to classic rim brakes, mechanical disc brakes are braked via a Bowden cable. The longer the cable, the greater the friction inherent in the system.
Hydraulic disc brakes, on the other hand, are braked with brake fluid. Because their friction losses are lower, their modulation and braking force are also better. These advantages come at the cost of higher costs and greater mechanical complexity.
Most mechanical brakes work on one side with only one piston. The movable piston presses the disc against the inner pad, which is firmly anchored in the brake calliper. Hydraulic brakes, on the other hand, usually work with two pistons that brake the brake disc symmetrically from both sides.
Hydraulic brakes are usually very reliable, but require special tools for maintenance. For example, they need to be bled during initial installation and often also later during maintenance. Compared to this, the brake cables of mechanical brakes are susceptible to rust and dirt, but they are easier to repair.
6. are all brake fluids the same for hydraulic brakes?
No. Some manufacturers use DOT (automotive) brake fluid, other manufacturers use mineral oil. The two types of brake fluid are not compatible with each other.
Avid/SRAM, Formula, Hayes and Hope use either DOT 4 or 5.1, both of which are glycol-based. Attention: DOT 5 is silicone-based and not compatible with DOT 4 or 5.1! DOT fluid has the advantage of a high boiling point, but has the disadvantage of being both toxic and hygroscopic. This means that it absorbs water from the air. DOT fluid is corrosive to both skin and bicycle paintwork and should therefore be wiped off as quickly as possible if it leaks. The boiling point of DOT 5.1 is slightly higher, but DOT 4 is available almost everywhere. The two can be interchanged.
Mineral oil, on the other hand, is chemically neutral and does not absorb water. It can remain in the brake system for years without having to be replaced. It is used by Magura, Shimano and Tektro used. According to our mechanics, the mineral oil used by Magura and Shimano can be interchanged without hesitation.
7 What happens if you accidentally bleed a mineral oil system with DOT or vice versa?
If you fill in the wrong brake fluid during maintenance, it's like the biggest accident you can imagine. The combination of DOT fluid and mineral oil brakes causes the seals to become "pitted" and soft. They are then destroyed, all sealing elements have to be replaced with new ones and the brake then reassembled. If mineral oil gets into a DOT brake, a kind of Viagra effect occurs: The seals swell and must also all be replaced. You should therefore always make sure you have the correct brake fluid.
8. which wheels are suitable for disc brakes?
With disc brakes, the front and rear wheel hubs must each have a mount for the disc on the left-hand side. The disc mount can be of different shapes, see question eight. Furthermore, the spokes must run at an angle to the rim so that they cross each other. A wheel with radial (= uncrossed) spoking is not suitable for disc brakes for reasons of stability.
9. what is the difference between hubs with IS2000 mount & centrelock? What about Rohloff & Pinion?
Most hubs use the IS2000 mount, also known as the "6-hole mount". The disc is screwed onto the hub with six M5 Torx screws.
With Centerlock, Shimano has introduced its own system with a multi-tooth profile and lockring. This makes assembly and disassembly a little quicker and the flange size of the hubs can be reduced slightly. The ring can be tightened with the normal cassette lockring tool. Rohloff uses its own 4-hole mounting system for brake discs due to the shape of its rear hub. In addition to Rohloff Avid, Formula, Hope, Magura and Trickstuff various discs in 4-hole format.
Pinion wheels do not need their own system, any suitable hub can be used.
10. can 6-hole discs also be mounted on centrelock hubs?
Yes, just fit a centrelock adapter to the disc and you can mount it on a centrelock hub.
Such adapters are available from Shimano as well as from third-party manufacturers and are relatively inexpensive.
11. why should you not touch brake discs directly after a ride?
The discs can get very hot! The main problem with all disc brakes is heat dissipation. If you have been riding on flat terrain without luggage and have not braked hard recently, the discs will not be too warm. But if you are riding with a lot of bags or in the mountains, the discs can get really hot. So if in doubt, don't take any risks - hands off!
12 Why are some brake discs one-piece, while others have a separate carrier?
IS or 6-hole discs are often made from a single piece of stainless steel. This is simple and reliable. Centrelock brake discs, on the other hand, always have an inner profile made of aluminium to accommodate the multi-tooth profile of the hub. If the profile is slightly larger and has several arms, it is called a "spider".
The outer steel disc is riveted to the spider. 6-hole discs are also often manufactured with a spider. Spiders provide additional stability, especially for large discs, and can be advantageous in the event of high thermal loads. If a brake disc heats up too much, it can become deformed. Spider constructions are generally somewhat more resistant to such deformations.
13. are the braking surfaces of the discs always made of solid steel?
Not necessarily. There have also been discs made of titanium, but they were very expensive and, above all, wore out quickly. Most brake discs are made of solid stainless steel, a material that has been tried and tested for a long time. For a few years now Shimano launched a new composite construction on the market with "IceTech".
The braking surfaces of the discs are made of steel, while the aluminium core in the middle should be better able to dissipate braking heat. New "IceTech" brake pads are also included.
14. what are the pros & cons of Shimano's "IceTech" & "Freeza"?
IceTech brake pads are fitted with cooling fins. With the "Freeza" technology, the IceTech aluminium core of the disc is enlarged and formed into cooling fins to keep it even cooler. Tests from BIKE and TOUR have shown that IceTech pads and discs do indeed dissipate heat well. Under normal conditions, IceTech brake discs work perfectly. However, if they are heated too much under extreme, yet realistic conditions, the aluminium core can melt and braking performance is suddenly reduced. Alpine cyclists and touring cyclists with a lot of luggage should therefore fit the largest possible brake discs made of solid steel.
15. can I use brake discs from other manufacturers?
Yes, first of all the size should be right, of course. If the disc is slightly too small, this is not disastrous, but it is not advantageous either. A disc that is slightly too large, on the other hand, can rub against the top of the brake calliper recess. Also check that the spider (if present) is not touching the brake calliper. As the new disc will be less worn than the old one, the brake pads may need to be readjusted if they are not replaced when the disc is changed. Some new brake discs, such as the Shimano SM-RT54, may only be used with organic pads.
16 What is the difference between metallic & organic coatings?
The term "organic" brake pads is misleading, they are not ecological brake pads. Organic simply means that such pads contain fewer metal elements and more fibreglass and resin. They brake better, especially in the wet, and they are quieter. Metallic pads have a longer service life and tend to squeal more.
17. do disc brakes have to be braked?
Yes, absolutely! Always read the operating instructions. With organic brake pads in particular, the brake pads must be heated to over 200 degrees by braking hard downhill so that solvents can outgas. Outgassing greatly reduces the braking force, resulting in so-called "fading". Therefore, when braking in, always brake with one brake only and keep the other in reserve. To be on the safe side, this procedure should be carried out away from any traffic.
18. why do my disc brakes squeal even though I have run them in?
If the brakes have been braked properly, it is probably because either the pads or the discs are dirty. Remember that chain oil, for example, must never get onto the pads, in which case they must be replaced. The discs can be cleaned with alcohol or special brake cleaner. The pads can be carefully cleaned and roughened with fine sandpaper.
19 How do I avoid transport damage?
You should never operate a disc brake if there is no disc in the brake calliper, for example if the wheels have been removed for transport.
In this case, manufacturers such as Magura offer plastic transport locks that are inserted into the brake calliper. However, if the brake pads have been pressed together, please do not push them apart with a screwdriver - this can scratch the pads! Instead, use the transport lock or something else made of plastic.
20 How often do disc brakes need to be serviced?
With mechanical brakes, the cables should be checked for ease of movement. Hydraulic brakes with DOT fluid must be refilled from time to time. Disc brakes should be checked at least once a year. Replace the brake pads when they reach a residual thickness of 0.5 mm at the latest. Also measure the disc thickness. If the thickness falls below the minimum thickness (sometimes printed on the discs, otherwise check the manufacturer's instructions), they must also be replaced.
