Floating disc rotors MAGURA MDR-P

A little history

Let's first dig a little into the history of floating discs before we get into the details of the MAGURA MDR-P or MAGURA MDR-P Center Lock semi-floating discs.

The reason why floating discs were developed was to ensure optimum braking performance at high speeds and temperatures. The first ever floating discs were thus used where else than in the automotive industry, or in racing motorsport. Specifically, Brembo played a key role in the development of advanced braking systems and introduced some of the first floating brake discs in the 1970s. These discs were used on Formula 1 race cars where it was essential to ensure optimum braking performance at high speeds and temperatures. The first two-piece Brembo floating discs were used in Ferrari cars in 1987-1991.

The use of floating discs has also been transferred from the automotive industry to motorcycle racing motorsport, where the need to optimize the twisting that occurs during turns on the wheels of motorcycles (knocking), especially in sports or racing bikes, and thus achieve stable braking performance even in moments when the disc is slightly bent off its normal axis of rotation, which a rigidly connected caliper with the fork or frame of the bike could not compensate. Suzuki was one of the first bikes to be equipped with floating discs, specifically the RG 500 for Grand Prix racing in 1975.

From motorbikes it was only a step to cycling and so floating discs were subsequently introduced to brakes used in cycling and especially in MTB or mountain bikes, where it was necessary to react to high temperatures and loads close to motorbikes. However, compared to motorcycles, cycling generally uses semi-floating discs rather than full-floating discs, which have a small amount of play in the pins only in the plane of the disc (or in the direction of rotation of the disc), because there is less need to compensate for the twisting of forks and frames, so there is not as much load (generally lower speeds, lower centrifugal forces and less weight and pressure on the whole braking system).

Full floating vs. semi-floating discs

For the sake of clarity, the difference between a full-floating brake disc and a semi-floating brake disc should be clarified. The difference between full-floating and semi-floating brake discs is the freedom of movement of the outer ring (braking surface) in the rivets relative to the inner sleeve, which affects their performance and use.

A full-floating disc has the braking or friction surface separated from the inner sleeve by special fasteners, often rivets in combination with support springs. A full-floating brake disc has freedom of movement in both the axial (lateral direction) and radial direction (direction of rotation). These movement options allow better compensation for thermal expansion, deformation during braking and disc twisting inside the brake caliper.

A semi-floating disc, like a full-floating disc, has a braking or friction surface separated from the inner sleeve by special fasteners, often rivets in combination with support springs. The fundamental difference, however, comes in the freedom of movement of the disc, where the semi-floating disc has freedom of movement only in the radial direction (direction of rotation). This freedom of movement only allows better compensation for thermal expansion and deformation during braking. That's all.

This small difference in freedom of movement, however, fundamentally changes how the disc behaves, where clearances can and cannot arise, and also what the disc can deliver in terms of benefits.

Generally both groups are called floating discs, but it is important to distinguish their specific characteristics. In the world of cycling and especially MTB cycling only semi-floating or semi-floating discs are used and not full-floating or full-floating discs. Full-floating discs have no justification.

MAGURA MDR-P disc brake design

If you thought all discs were made of the same material - simply steel, you couldn't be further from the truth. MAGURA MDR-P discs are made of martensitic chrome steel with anti-corrosive treatment on the outer part (the braking surface of the disc). What does this mean? The chromium here serves to make the steel corrosion-resistant, while the carbon allows the martensitic structure to form during heat treatment, giving it high hardness. The martensitic structure is a microstructure that is formed by rapid cooling of austenitic steel (i.e. steel heated to a high temperature), causing austenite to convert to martensite. This process produces hardness but also brittleness. Martensitic chromium steels are used where a combination of high strength, wear resistance and some corrosion resistance is required. This steel has been specifically designed to work best in combination with MAGURA brake pads and so if you are wondering what pads to use on your bike with MAGURA discs, there is no easier answer than - MAGURA pads. As mentioned above, there is no steel like steel :-).

The inner sleeve is made of a special alloy of aluminium, magnesium and silicon. This combination of elements creates an alloy with excellent mechanical properties that are often used in various industrial applications. This alloy combines the advantages of lightweight aluminium with the strength benefits of magnesium and silicon. Aluminium is the most abundant material and gives the inner sleeve its lightness and corrosion resistance. Magnesium adds high strength to the alloy and improves its tensile strength. Magnesium also increases the ability of the alloy to undergo heat treatment, allowing for further strengthening. Silicon improves the casting properties of the alloy, lowering the melting point and increasing strength and hardness. Again, you thought it was easy? Not at all! There is no aluminium like aluminium :-).

MAGURA MDR-P discs are of semi-floating design. Its purpose and advantages have been mentioned in the paragraphs above. This technology is nothing new, but it is not a completely common construction in the field of cycling, because its mastery requires considerable knowledge, high-quality production technology and other specifics without which such a disc would be impossible to produce. The MAGURA MDR-P disc consists of an outer steel ring (braking surface) and an inner aluminium carrier (6 bolt hub mount, or Center Lock). MAGURA uses 6 small pins with special spring washers to connect the outer steel ring and the inner aluminium sleeve.

MAGURA MDR-P discs are unique thanks to a patented technology called Dovetail Interlink Technology. Compared to conventional semi-floating discs, where the outer steel ring and the inner aluminium sleeve are only connected by pins and no other surfaces are touching, the MAGURA MDR-P disc is different because it is equipped with additional elements that interlock in case of high load. The "toothed" part of the outer steel ring can (as mentioned above) move freely in the pins in the fore-aft direction in the event of a high load. In the case of high load, the "toothed" parts of the outer ring and the inner aluminium sleeve come into contact with each other and part of the pressure from the pins is thus taken up by the contact between these two components of the disc and thus the braking power is transferred to the hub or wheel not only via the disc pins but over a much larger area. This technology therefore prevents overloading of the pins and consequent twisting of the disc while maintaining the advantages of a semi-floating design.

In order to achieve the required properties, heat resistance, high performance under any conditions, etc., MAGURA MDR-P discs are 2.0mm thick in their default state and their limit of run-out is 1.8mm. It is strongly recommended not to exceed the run-in limit, as the brake pistons will then come out more from the brake caliper body and may cause damage to the brake system (high fluid loss in the brake lever overflow chamber and damage to the overflow chamber seal), overloading of the pistons (they will be more stressed by lateral forces) and overall deterioration of braking performance!

Pin clearance of MAGURA MDR-P discs

We are coming to a very interesting topic that is not entirely clear to everyone. The clearance or movement of the outer steel ring relative to the central aluminium sleeve. Is that okay or not? Yes and no.

As mentioned above, the MAGURA MDR-P is semi-floating. As we have explained, the construction is designed so that the outer steel ring (braking surface) can expand more freely relative to the centre sleeve and the braking surface can then move in a fore and aft direction of rotation. So yes, the pin clearance in the MAGURA MDR-P disc is a design feature and not a defect as many think.

The information on the official MAGURA website points to this problem, see here: https://magura.com/en/EUR/service?serviceItemType=FAQServiceEntryType&serviceEntryId=maguracom_bauweise_mdr-p_faq

In addition, MAGURA uses the aforementioned Dovetail Interlink Technology, which would not work at all without the front-to-back movement of the outer ring and would not make sense.

However, the front to rear clearance of the outer ring should not exceed 1mm (1mm forward and 1mm backward). However, if you notice more play, or even side play, and the disc makes various clunking and resonating noises while driving, it is advisable to replace the disc.

Brake discs MAGURA MDR-P and MDR-P Center Lock

MAGURA MDR-P discs are available in both common wheel hub mounting options. Respectively, the disc is available MAGURA MDR-P for standard 6-bolt, or also a disc MAGURA MDR-P CL for Center Lock.

For both versions you will find everything you need to attach them to the wheel hub in the package. For the 6-bolt version you will find 6x torx T25 bolt and for the Center Lock version 1x tightening nut. What is important with both mounts is to pay attention to the maximum tightening torques for both versions. The MAGURA MDR-P 6 bolt disc has a maximum tightening torque of 6 Nm per bolt and the MAGURA MDR-P Center Lock disc has a maximum tightening torque for the nut set at 40 Nm. Another reason to finally use a torque wrench to tighten the bolts on your bike :-).

The following averages are available for each version in terms of dimensions and weights.

MAGURA MDR-P (6-bolt)

• 180mm - 190g
• 203mm - 216g
• 220mm - 241g

Weights shown are without the 6 steel bolts for attaching to the hub that are included with the reel. These 6 screws weigh an additional 15g.

MAGURA MDR-P CL (Center Lock)

• 180mm - 211g
• 203mm - 226g

Weights shown are without the tightening nut for attachment to the hub, which is included with the reel. This nut weighs an additional 15g.

You will have noticed that the MDR-P disc in the Center Lock version is not available in 220mm diameter. Yes it is, and MAGURA has not yet released any information that this will change. So if you own a hub with a Center Lock mount and are going to purchase this type of disc, 203mm is the maximum disc diameter you can use.

Do not use adapters for Center Lock!

On most semi-floating brake discs designed for 6-bolt hubs, you will find information that you should not use the Center Lock to 6-bolt adapter.

The first problem is the possible increase in clearance. Each such adapter adds some small deviation to the system. That is, if you use this adapter, you will add more clearance to the system, or "vacuum" in the lateral direction (rotation of the disc), and the clearance that the disc has from its principle of construction (it is semi-floating), manifested in the pins after a certain time and several cycles of heating and cooling, you will increase this adapter. This means that you increase the already normal clearance of the disc (1mm in the lateral direction) in the pins by another and this can have an overall effect on comfort.

At the same time, it is often written in the instructions that this clearance can cause the disc to scrub more against the pads. So, for example, with MAGURA MT7 PRO where the pads are already very close to the disc (because of its design and better and clearer dosing - the pads touch the disc earlier and so in a larger lever step you are dosing the power) you may struggle with the pads clinking or rubbing constantly against the disc and the system will be noisy.

It is also mentioned that it can have play in the radial direction, i.e. up and down, when using this adapter and can cause scrubbing on the caliper or changing the position of the brake pads up and down. This can result in asymmetrical sliding of the disc and pads and this in turn will affect the quality of braking performance which can be quite erratic.

Most often, it is not possible to use the Center Lock to 6-screw adapter on reels that have an aluminum sleeve - which is the MAGURA MDR-P. The reason is simple. By inserting the adapter into the aluminum carrier, you can cause the disc to squeeze out the holes that are designed to be tightened firmly with the screws and not the Center Lock nut.

We definitely recommend using MAGURA MDR-P Center Lock discs for Center Lock hubs and MAGURA MDR-P discs for 6 screw hubs.

One more thing to note. The tightening torque of the nut for the Center Lock is 40Nm. The Center Lock disc is adapted to this by its construction, where the part where the bolt holes are otherwise is reinforced, there are no holes drilled for bolts and the disc is thus adapted to this high tightening torque around the perimeter of the hub mounting.

The MDR-P 6-bolt disc is structurally different, at least at its center where it is attached to the hub. It is thickened, has holes for screws and the tightening torque of one screw is then max 4,5Nm and not almost 10 times as much.

If you tighten the Center Lock nut on a weakened 40Nm disc you are putting much more pressure on the center of the disc than it is ready for and risking a problem. This probably won't show up immediately, probably not with the first brake, but after a while when the disc is tired it will have gone through several warm up and cool down cycles. Gradually, the disc will have more "vacuum" due to the adapter, it will be more run down and will get hotter all over due to that and you will be, let's say, close to the life limit. That's when a major problem can occur and the disc can fail.

It's certainly not smart to bring a combination of these problems into the safety system that is brakes!

All the above reasons are therefore simply and abbreviated directly on the MDR-P reel by the phrase NOT FOR CL ADAPTER USE. Because no adapter is so safe and reliable (which a braking system must be) that MAGURA can safely tell you to put an adapter in. She couldn't....

Designation of MAGURA MDR-P discs

It is important to note that the MAGURA MDR-P disc was not developed and is not intended for regular MTB bikes such as XC, Trail, etc. This disc has its application in demanding Gravity disciplines such as Enduro, DH, Freeride and especially in the electric bikes or eBike segment. The MAGURA MDR-P disc was developed for these disciplines and its weight, design, etc. corresponds to this.

So if you are planning to get this disc for your MTB trail bike, it's not quite the right choice. The disc will not heat up enough and the pads and brake compound will never get to their proper thermal efficiency. Plus, you'll add completely unnecessary extra weight to your bike. Then choose the MAGURA MDR-C or STORM HC one-piece discs instead.

The MAGURA MDR-P disc is also equipped with a hole in which a magnet for the wheel speed sensor can be placed. This is mainly used on eBike bikes. However, a specific MAGURA magnet for speed sensors must be purchased, as other magnets are unlikely to be compatible with the MAGURA MDR-P disc.

Conclusion

MAGURA MDR-P discs are an interesting upgrade for demanding riders. The discs are designed especially for use on eBikes and for demanding riders focusing on Gravity disciplines such as Enduro, DH or downhill, or Freeride.

But with MAGURA MDR-P discs you have to take into account the increase in weight of the braking system, so if you are chasing every gram, these discs are not for you.

If you're a light rider and don't need the highest possible performance, or temperature resistance, etc., then consider getting discs with less metal mass, such as MAGURA MDR-C or STORM HC.

Be sure not to use the MAGRUA MDR-P for 6 bolt attachment with Center Lock adapters on Center Lock hubs. You are really risking a lot of trouble and your life!

I believe you now have all the information you need to know if the MAGRUA MDR-P or MDR-P Center Lock discs are right for you.