This post compares the advantages and disadvantages of 160mm and 180mm disc brake rotors.
The Advantages of 180mm Rotors
1. Greater Stopping Power
180mm rotors are larger and require the caliper to be positioned further away from the center of the rotor. The extra distance gives the caliper greater leverage on the rotor resulting in more stopping power.
The additional mechanical advantage lowers the physical effort needed to brake or slow down too.
When all other parameters are equal (brake type, pads, levers…etc.), the same squeeze of the lever produces more stopping power when the rotor is bigger.
2. Better Heat Dissipation
During long descents, brake rotors tend to overheat due to constant friction against the brake pads.
Larger rotors have better heat dissipation thanks to the greater thermal mass.
Overheating of the rotor has the following consequences:
a. Loss of braking power + Damage to the brake pads
A hot rotor softens the brake pads to the point where the pad’s upper layer melts and gets on the rotor. Some refer to this phenomenon as “painting of the rotor”. Once the rotor is “painted”, its surface is no longer pure metal.
When the rider presses the brakes, the friction between the pads and the rotor isn’t as great because of the contaminated surface of the rotor. The result is a noticeable loss of braking power.
b. Disc warping
Overheating of the brakes can cause disc warping too.
Disc warping is a process during which the surface of the rotor becomes uneven as a consequence of rubbing against deformed pads.
Overheating speeds up this outcome because the heat damages the pads unevenly. In return, the deformed pads cause surficial deformation of the rotor.
3. Better for Heavier Individuals and Loaded Bikes
The greater the mass, the more braking power is needed to stop the bicycle. For that reason, 180mm rotors are recommended to individuals on the heavier side and to people who transport heavy cargo (e.g., touring cyclists.)
The Downsides of 180mm Rotors
1. Higher Chances of Brake Rubbing
180mm rotors have a longer radius than 160mm rotors. As a result, a smaller bend gets the rotor closer to the pad and causes annoying rubbing. Hence why 180mm rotors may need a more frequent realignment.
2. Bigger Rotors Are Easier to Bend
180mm rotors have a larger body and are more likely to get damaged while riding or transporting the bike.
3. More Aggressive Modulation
Larger rotors offer higher mechanical advantage and grab earlier. Some people don’t like that because some of the brake modulation is lost.
The term brake modulation describes the ability to apply and control the braking force.
If a set of brakes has too much modulation, the brakes will bottom out (arrive at the end of their travel) before reaching full braking power.
If there’s too little modulation, braking is stiff, there’s little feedback, and the brakes work in on/off mode with small or no phases in-between.
180mm rotors are larger and heavier than 160mm models. People who want to keep their bikes as light as possible won’t like that.
The table below compares the weight of popular 180mm and 160mm rotors:
|NOW8 Float||108g||NOW8 Ultralight disc||67g|
|Magura MDR-C – 6-Bolt||162g||Jagwire Sport SR1||129g|
|Magura MDR-C – Centerlock||190g||Trickstuff Dächle HeavyDuty||111g|
|FSA Afterburner||155g||Rotor UNO||95g|
|NOW8 Ultralight disc||93g||NOW8 Float||108g|
|Magura Storm Rotor||152g||Magura MDR-C||140g|
|SRAM Centerline Round Edges Rotor||112g||SRAM Centerline Round Edges||112g|
|Shimano Deore XT SM-RT86||136g||FSA Afterburner||125g|
|Jagwire Sport SR1||153g||Carbon-Ti X-Rotor SteelCarbon 2||77g|
|Trickstuff Dächle HeavyDuty||154g||Shimano RT86 Ice-Tech||113g|
|Average:||141.5g / 4.99oz||Average:||107.7g / 3.79oz|
Conclusion: On average, 160mm rotors are 33.8grams (23.8%) lighter than 180mm models. If you run a pair, the weight savings double to 67.6 grams.
Truth be told, 67grams are not enough to make a perceivable difference, especially in the world of amateur and recreational cycling.
FAQ: 180mm Front + 160mm Back or Double 180mm?
It’s not uncommon for cyclists to combine different size rotors. Usually, the bigger one is installed at the front to maximally boost the overall stopping power of the bike.
Because the front brake offers a much greater deceleration than the rear. When you add a bigger rotor to the front, the overall braking potential rises more than it would if you were to install the larger rotor on the back.
Conversely, the rear brake is used primarily to decelerate rather than to stop completely.
For that reason, it makes more sense to install the smaller rotor on the back and benefit from the extra modulation when slowing down.
The Advantages of 160mm Rotors
160mm rotors have the following pros:
Smaller rotors require less material and are therefore less expensive than bigger ones.
2. No need for adapters
Most frames and forks designed for disc brakes can accept 160mm rotors by default. Meanwhile, if you want to switch to a bigger rotor such as 180mm, you will need an adaptor designed for your particular mounting system.
The purpose of the adapter is to get the caliper further away from the mount.
3. Less “grabby”
More stopping power isn’t always desirable because it shortens the travel, reduces modulation and makes braking feel like an on/off switch rather than a smooth, gradual process.
5. Less Likely To Bend
Smaller rotors are not as exposed as larger models and are less likely to get damaged during riding or when transporting the bicycle.
6. Lower Chances Of Brake-Rub
160mm rotors have a smaller radius. As a result, it takes a larger bend to experience brake rubbing.
As already mentioned, 160mm rotors are a bit lighter than 180mm ones.
The Disadvantages of 160mm Rotors
In practice, 160mm rotors have only one notable downside in comparison to 180mm ones – less braking power. If you’re covering extreme descents, this could turn problematic.
Parameters to Take into Consideration When Making a Choice
1. Bike Size and Weight
The extra stopping power makes 180mm rotors more popular on 29-ers.
29-inch tires have a greater rotational mass and benefit from the extra stopping power.
However, if you have a bicycle with smaller wheels (e.g., 26-inch), the rotating mass is smaller and doesn’t always necessitate more powerful brakes.
2. Riding Style + Terrain
A bike that’s going to be used for extreme descents would greatly benefit from stronger brakes.
Meanwhile, a commuter bicycle ridden mostly on flat, paved roads doesn’t require the braking power of a downhill MTB.
3. Rider’s Weight
The rider’s weight is also a part of the equation. A heavier rider equals more moving mass requiring more braking power.
In conclusion, a light rider (e.g., 170lbs) on a bike with smaller wheels (e.g., 26-inch) doesn’t benefit as much from 180mm rotors as a heavier cyclist (e.g., 200lbs+) on a large bike with massive 29-inch wheels.
How to Switch From 160mm to 180mm Rotors (Short Guideline)
Step 1: Determine the Type of Disc Mounts That You Have
There are three types of disc brake mounts – International Standard, Post Mount and Flat Mount
International Standard (IS) is found on older forks and frames. The brake caliper attaches via bolts screwing perpendicularly to the mount. Modern fork manufacturers have completely abandoned the International Standard.
If you have IS mounts and want to switch from 160mm to 180mm rotors, you will need a +20 IS to Post Mount adapter.
Post Mount (PM) is found on modern bikes. The caliper attaches via bolts going straight into the mount.
If you have PMs designed to run 160mm rotors by default and want to upgrade to 180mm, you will need a 20mm post mount adapter.
Flat Mount (FM)
Flat mount is a fairly new disc mount standard found on road bikes. The caliper attaches to a flat part of the fork or frame. The goal is weight saving and simplicity.
Currently, flat mounts are limited to 160mm rotors, and you won’t be able to install larger ones.
Step 2. Install the Calipers
Once you have the right adapter on, install the brake calipers.
Step 3: Replace the Old Rotors
Remove the wheel, unscrew the rotors and screw on the new ones. Get the bolts to the torque required by the brake manufacturer.
Step 4: Install the Wheels
Summary: What You Need To Know
1. 180mm rotors offer greater stopping power than 160mm ones and are better for larger riders and harsh descents.
2. 160mm rotors are lighter, provide better modulation and work just fine for small riders and bikes that won’t be used for downhill.
3. You can switch from 160mm to 180mm by installing a mount adapter.
4. Many people run a 180mm rotor at the front for maximum braking power and 160mm at the back for greater modulation.