Friday, October 30

Disc Bicycle Brakes: What is the Ideal Rotor Size?


Source: Cyclist post

LONDON, U.K. – Disc brakes. First endurance bikes had them, which was easy to justify. Their more consistent performance was a natural fit on rough roads in often changeable weather conditions.

Then aero race bikes got them, which again made sense. Weight is not such an issue with aero bikes, and disc brakes opened opportunities for aerodynamic development.

Yet now even lightweight race bikes have them. Disc brakes are no longer the braking system of the future – they are the braking system of the present. Discs are the new normal, and with that maturation has come a settlement on certain standards.

Related post:
Bicycle Brake superiority: Disc or Rim in Tour de France

For example, flat-mount, where the brake caliper sits directly on a chainstay or fork blade, as opposed to post mount, has been universally adopted. However, there is an area where a certain amount of debate still exists, and that is around the size of disc rotors.

Should all disc bikes use a pair of 160mm rotors? Why not 140mm, 180mm or even a mixed pair? While several factors enter the mix when it comes to design decisions that account for the current discrepancies, most importantly calls are made based on safety.

“In my opinion a pair of 140mm rotors look nicest, but as many riders are over 80kg there is a chance braking performance can be affected in certain conditions,” said Giacomo Sartore, group set product manager at Campagnolo.

“This is why we recommend either a pair of 160mm rotors or 160mm front, 140mm rear. With those options a rider can drag their brakes all the way down the Stelvio and not suffer any dip in performance.”

Sram’s road product manager, Brad Menna, agreed, “We recommend 160mm for road applications. That’s what provides the most power and best system performance for the widest range of riders and uses.”

Shimano’s Ben Hillsdon also agrees and explains why 160mm rotors might be better able to cope in certain situations.

“When brake caliper pistons are applied to larger rotors, due to the fact that they are further away from the rotating axle, they provide greater leverage and torque to stop the rotation,” he said.

Menna added that bigger rotors also have a larger braking surface to dissipate heat, “The better you manage heat, the more consistent the brakes work under various loads.”

Given that evidence, it would be reasonable to assume that the case for a pair of 160mm rotors would be cut and dried, but a mixed setup – with 160mm at the front and 140mm at the rear – is just as popular.

The entire post can be viewed by clicking HERE.

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