А 200mm rotor can be installed on calipers designed for 203mm rotors without modifications apart from removing a set of washers (not always needed).
Installing a 203mm rotor on 200mm mounts requires the installation of additional 1.6mm spacers.
Thus, in practice, the rotors can be seen as interchangeable to a large degree.
What is the difference between 200mm and 203mm rotors?
Apart from peculiarities that apply to specific models, the only difference is the diameter. 203mm rotors have a 1.5 larger radius and consequently a 3mm bigger diameter.
Technically, the additional 3mm should provide more stopping power because larger rotors have a greater mechanical advantage over the wheel. The principle is the same as when one uses a cheater bar (longer wrench handle) to untighten a bolt.
That said, the additional 3 millimeters increase the diameter of the rotor by only 1.48% and the radius by 0.74%. Thus, one can say that the extra braking power is inconsequential in the big scheme of things.
The state of the rotors and brake pads has a much larger impact on braking power than 0.74% more leverage (we use the radius rather than the diameter to determine the additional leverage because brake pads grab the rotor at a single location.)
Installing a 203mm Rotor On a 200mm Mount
Some 200mm calipers & mounts will readily accept a 203mm rotor without rubbing. However, in many cases, there won’t be enough clearance between the rotor and the caliper.
In that instance, the go-to solution is to add washers with 1.5-1.6mm thickness between the brake mount and the disc brake caliper. The washer will push the caliper further away and create space for the rotor.
Disc brake mounts operate with M6 bolts that are 18-20mm long. Thus, the inner diameter of the washers will have to be 6.4mm or 0.25 inches.
The vast majority of washers with that size have a 1.6mm thickness and will therefore be sufficient to distance the rotor from the caliper.
200mm Rotor On 203mm Mount
If the mounts are designed for 203mm rotors, then a 200mm rotor has enough clearance by default.
The downside is that in some cases the pads could experience slide “brake pad overhang” because a part of them will not be in contact with the rotor.
When the rotor is smaller than originally intended, a section of the pads never touches the rotor.
Consequently, that section never gets smaller because there’s no friction between it and the rotor. The rest of the pads, however, get smaller with time.
Eventually, the sections of the pads that never come in contact with the rotor touch each other and prevent the brakes from closing further. As a result, the brake fails to close sufficiently to grab the rotor and slow down the wheel. Thus, brake pad overhang makes a brake useless over time.
That said, in this particular case, this phenomenon may never take place because the difference in rotor radius is small.
To be certain, however, close the brake and see if the entire brake pad comes in contact with the rotor. If it doesn’t, brake pad overhang could develop in the future.
There are two ways to remedy this situation:
A. Get the correct rotor, in this case, 203mm.
B. Remove one set of washers sitting between the brake mount and the caliper.
By removing the washers, the pads will get closer to the center of the rotor. This should eliminate the disc brake overhang.
Before doing so, consult the manufacturer of the brake to see if this practice voids their warranty.
How Can I Convert From My Existing Rotors To 200mm or 203mm?
Step 1: Determine Your Brake Mount and Current Rotor Size
The brake mount refers to the architecture on the fork and frame to which the caliper attaches.
The possible mounts are:
International Standard (IS). The brake caliper is attached to the frame and fork via bolts screwing perpendicularly to the mount. This is an older standard, and you will not find it on modern suspension forks.
Post Mount (PM). This is the most common disc brake mount. The caliper is mounted via bolts going directly into the mount.
Flat mount (FM). This is a fairly new disc mount common for road bikes. The mounts are very slick and discrete. Flat mounts are limited to 160mm rotors and therefore cannot be converted to 200/203mm.
Step 3: Find the right adapter
The adapter that you need is dependent on your brake mount and current rotor size.
For example, if you have 180mm rotors with a post-mount, you will need a +20/23mm post-mount adapter.
The list below contains the rest of the possibilities:
|Mount and Rotor Size
FAQ: What are the advantages of upgrading to large (200/203mm) rotors?
More stopping power thanks to the additional leverage coming from the longer radius. For instance, the radius difference between 160mm and 200mm rotors is 20mm. This is a 20% difference that one will notice.
If you can upgrade only one wheel, it’s recommended to go for the front as it produces more stopping power.
The front end gains additional traction when stopping and thus provides 70% or more of a vehicle’s stopping power.
Another advantage of larger rotors is the additional heat dissipation that happens thanks to a wider body. This property is fundamental for extremely long descents.
If the rotors heat up to a high temperature due to the friction against the pads, friction fade could occur.
Friction fade is a process during which the hot rotor melts the upper layer of the brake pad. The deteriorated brake pad layer leaves a semi-liquid imprint on the rotor resulting in lubrication and loss of friction. The result is a less of braking power.
FAQ: What type of mounting systems do 200mm and 203mm rotors use?
It depends on the manufacturer. For instance, all Shimano rotors use the patented Centerlock mounting system.
The Centerlock system requires a special hub with a spline. The rotor goes onto the spline and is then secured with a lock ring. You can read more about the technology here.
Shimano doesn’t officially make 200mm (at least at the moment). Thus, if you have a 203mm rotor from Shimano, you will have to rely on the Centerlock mechanism.
Meanwhile, 200mm rotors are made by many companies and rely on a 6-bolt mounting system. It’s possible to install a bolted rotor to a Centerlock hub with the help of an adapter. (image below)
FAQ: What is the difference between 180mm and 203mm rotors?
The only major difference between 180mm and 203mm rotors is the size/diameter and weight. All things being equal, 203mm rotors are heavier than 180mm models but provide better stopping power, as explained above.
Both will work well for most people, but if you are doing extreme descents with an MTB, larger rotors are a better option.
FAQ: What type of bikes use 200 and 203mm rotors?
200 and 203mm rotors are reserved for MTBs (enduro, downhill). They can also be found on freestyle bikes and some XC bikes.
FAQ: What brands make 203mm rotors?
Shimano is the main one followed by SRAM, Avid, and Hope. Of course, there are other manufacturers too.
Summary: What You Need To Know
- 200mm and 203mm are not fully interchangeable but with a small modification to the brake caliper, they can be.
- To mount a 203mm rotor on a caliper otherwise designed for 200mm models, it will be necessary to add a washer with 1.6mm thickness between the brake mount and the caliper. This will create space for the larger rotor.
- If you want to mount a 200mm rotor on a 203mm system, it may be necessary to remove a washer between the caliper and the mount to avoid brake overhang (the phenomenon is explained at the beginning of the post.)
- It’s possible to upgrade from a smaller rotor (e.g., 160, 180mm) to 200mm or 203mm by using an adapter for your specific brake mount.
- Larger rotors provide more stopping power thanks to their additional leverage against the wheels.
- The larger body of 200mm and 203mm rotors has better heat dissipation and reduces the chances of friction fading.
- The difference in stopping power between 200mm and 203mm is negligible.