Condensed answer: The braking surface of Campagnolo rotors is slightly wider than that of Shimano models. Consequently, the brake pads of a Shimano road caliper would cover about 4/5 of the new brake track.
The result is a slight loss of braking power in wet conditions. The difference isn’t dramatic, but for optimal performance, it’s recommended to use the appropriate rotors for the system.
The brake track is the part of the rotor that the brake pads squeeze when the rider initiates a stop.
- If the pads are larger than the brake track, brake pad overhang will occur.
- If the brake track is a lot wider than the brake pads, a slight loss of stopping power could occur.
(Side note: Brake pad overhang is a phenomenon during which a section of the pads never gets smaller because there’s no friction between it and the rotor. The rest of the pads, however, gets smaller with time.
Eventually, the parts 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. At that point, the brake is useless.)
When mixing Shimano calipers and Campagnolo rotors, we observe the second phenomenon, namely insufficient contact between the pads and the rotors.
This happens because the pads of Shimano’s road calipers are designed for a narrower brake track. As a result, the brake pad does not cover the entire brake track (only 4/5).
For example, the braking surface of Campagnolo 160mm rotors is approximately 16mm. Meanwhile, that of Shimano’s 160mm rotors is 15.5mm. The brake pads have to reflect the 0.5mm difference.
The smaller contact is not perceivable in dry conditions but could become more noticeable in the rain. For that reason, it’s recommended, to either switch to Campagnolo calipers (more expensive) or purchase dedicated Shimano rotors of the appropriate size for your bike (cheaper option).
Is the difference substantial enough?
The difference in brake track width between the two types of rotors is not massive, and it would be inaccurate to conclude that the combination simply doesn’t work. The brakes would still provide plenty of stopping power in most cases. But if optimal performance is needed, then it’s wiser to use the recommended rotors.
What about thickness?
Shimano rotors are 1.8mm thick whereas Campagnolo models are 1.85mm. The 0.05mm difference is not substantial enough to cause complete incompatibility. If the pads’ position is correctly set, there will be no unwanted rubbing between the rotors and the brake pads.
Summary: What You Need To Know
- If the Campagnolo rotors are of the correct size, they can be integrated into a Shimano brake system.
- The main downside is that the brake track of the Campagnolo rotors is slightly wider than that of Shimano’s rotors. As a result, there’s a slight loss of brake power that is more likely to manifest in wet conditions.
- The combination is still viable, it just isn’t optimal. Ideally, one would use the recommended Shimano rotors.