Road bike evolution is relentless.

Disc brakes are playing a central role in this evolution.

Indeed, disc brakes have become the mainstream for complete bikes.

At this point, I would like to reconsider disc brakes.

1. How have disc brakes changed road bikes?

First, let's consider how the shift to disc brakes has changed road bikes as a whole.

① Wider Rims and Wider Tires

In recent years, tires have become wider. As a result, rims also tend to be wider. While C17 was the standard for caliper brake specifications, disc specifications have expanded to C19-C21.

One reason for this is that disc brakes eliminate the need for a brake track, allowing for a reduction in rim weight. This weight saving can then be used to accommodate wider rims, despite a slight increase in overall weight.

However, this applies only to the rim. Considering the increased number of spokes and the added weight of the hub/rotor assembly, disc brakes are indeed at a disadvantage in terms of weight.

② Changes in Spoke Patterns

With the change from rim brakes, which grip the rim to stop, to disc brakes, which grip the axle to stop, spoke patterns now require greater strength. In particular, traditional radial lacing (a lacing pattern where spokes do not cross) is no longer sufficient for the front wheel to withstand stopping power. The number of spokes has also increased.

③ Relationship with Carbon Wheels

There were some concerns about the compatibility of carbon wheels and rim brakes, such as braking effectiveness, heat resistance, and wear of the brake track. The fact that disc brakes have resolved these issues is considered a major factor in their rapid adoption.

④ Changes in Riding Patterns

Improved control when braking heavily on descents is a significant advantage, allowing riders to descend more aggressively.

Disc brakes are also less affected by rain and mud, which is a welcome improvement in all-weather performance.

⑤ Symmetrical Rims

Due to the space required for the cassette, the spokes on the rear wheel are laced असymmetrically (referred to as a difference in dish). In response, some elaborate rims were designed with an asymmetric profile. However, with the addition of disc brake space on the opposite side of the cassette, the asymmetry is somewhat mitigated, and rims are increasingly tending to be symmetrical.

⑥ Other Changes

The shift from quick releases to thru-axles has increased axle rigidity, which also affects the ride. There are also changes in operation due to the altered feel of braking.

2. Points of discomfort that have emerged with the disc braking of road bikes

When I started using disc brakes, I found some areas that still felt a bit undeveloped. While many of these can be resolved with familiarity, I hope to see further improvements in the future.

① Squealing noise issues

Sometimes a jingling sound can be heard during out-of-saddle pedaling. This is attributed partly to contact with the pads due to thermal deformation of the rotor. This can be resolved to some extent by adjusting the pads to hit the center of the rotor, but the impression of the delicate disc complaining about the dynamic flexing of the frame is not very pleasant.

② Brake feel issues

While disc brakes offer excellent stopping power, rim brakes still have an advantage in terms of delicate control, and this continues to be a point of discussion.  

③ Issues during wheel removal and attachment

There are no issues if proper removal and attachment procedures are followed, but it is repeatedly brought to my attention that they cannot withstand rough handling like rim brakes. (I will touch on this again in the next chapter.)

④ Issues during bike travel (rinko)

In addition to removal and attachment, protecting the disc surface and inserting spacers between the pads require a lot of care, which becomes particularly apparent during bike travel. It is common to hear that cyclists who own both disc and rim brake bikes choose the rim brake option when traveling.

3. Important points to note when handling disc brakes

① Thru-axle standards

While wheel fixing standards are becoming more unified, thru-axle standards vary.

When assembling separately, it is generally recommended to use the thru-axle that comes with the frame. However, since it may not be included, it is necessary to confirm this at the time of purchase.

② Burn injury issues

It's well known that the rotor can cause burns due to heat immediately after riding. Even though you know this, you might accidentally touch it while changing a tube or something, so caution is needed. Also, splashing water on a hot rotor can cause deformation.

③ When replacing wheels

You must carefully ensure that the rotor enters correctly between the left and right pads, while avoiding damaging the caliper or mounting with the rotor. For the rear wheel, it's easy to make a mistake during replacement if the chain tension is applied, so it's necessary to shift to the top gear and remove the chain from the front chainring, among other considerations. After installation, the rotor's position may be slightly off, so it's recommended to readjust it.

④ When travelling with your bike (rinko)

As mentioned in the previous chapter, utmost care is required. If you discover a deformed rotor when trying to assemble it at your destination, it's too late. Covering the entire wheel is a good preventative measure.

⑤ When cleaning

When cleaning, check the wear of the pads and rotors. The pads should only be wiped clean, and absolutely no oil should be applied to the rotor, not even hand oil, and avoid touching the contact surface.

If oil accidentally gets on the rotor, carefully wash it off with a neutral detergent.

This story continues in the next chapter.

4. Disc Brake Maintenance

① General premise

Brake components should not come into contact with oil. The following common mistakes should be avoided:

• Spraying oil (such as spray lubricant) on parts near the brake, such as the chain (which can get on the brake) ✕
• Touching the rotor with your hands ✕
• Using parts cleaner (which contains oil) ✕
• Touching brake parts with a dirty rag ✕

② DIY Maintenance

Since many disc brake maintenance tasks are unfamiliar, proceed with extreme caution.

• Rotor tightening: If using screws, tighten one, then tighten the screw 180 degrees opposite.
• Pad/Rotor replacement: Possible with careful execution; requires simple specialized tools.
• Rotor distortion correction: Minor distortions can be corrected by hand, but direct contact is forbidden.
• Caliper centering: Loosen the caliper fixing screws, squeeze the brake lever, and while holding it, retighten the screws (a disc rotor centering tool can also be used).
• Brake lever adjustment: Adjust with the screw inside the bracket cover.

I believe these tasks are generally within the scope of what you can do yourself.

Tasks involving brake fluid replacement might be difficult unless you have thoroughly researched them.

5. Conclusion

Shimano has finally released the new Dura-Ace R9200, along with the Ultegra R8100 series, causing a stir in the industry.

Shimano has provided an answer regarding disc brakes. It seems there have been significant improvements from the previous notion that "disc brakes have good stopping power, but rim brakes offer superior control." This could potentially be the final push for the widespread adoption of disc brakes in racing.

ICAN will also continue to observe the disc brake situation with keen interest. Ⓗ