I have a old 86 Honda Rebel and my dad has a much newer Honda, and I never really noticed it before until i worked on the disc brakes for my Bronco then i noticed that both of the bike's disc brakes had holes in them
THE ONLY REASON WHY DISK BREAKS HAVE HOLES IS BECAUSE OF HEAT TRANSFER. THE HOLES FUNCTION AS A HEAT DISSIPATION. FRICTION IS PRODUCED WHEN THE BREAK PAD MADE CONTACT WITH THE DISK BREAK. IT HELPS COOL THE DISK BREAK, TO LET THE HEAT TRANSFER TO ATMOSPHERE! - MECHANICAL ENGINEERING ;)
Gives water a place to go which improves wet weather performance, better heat dissipation and lighter weight-those were the original reasons. However, I noticed that the latest BMW cars no longer have drilled rotors, don t know why.
Nothing to do with cooling at all. The holes are there to assist in the wiping of water off the disc so they work as well in the wet as in the dry - like tread on a tyre. the previous two answerers are getting confused with ventilated discs, which are like two thin discs very close together with a narrow gap between them.
All the reasons stated are correct: cooling:more surface area friction:more change in grip when braking water drain:serves as tread weight:an obvious desirable side effect Here is something they missed out: The holes are spaced in such a way that the calipers used in the brake wear out uniformly, to ensure maximum longevity.
The holes do a few different tasks. Less weight for starters. The holes have a cheese grater effect on the pads, signifigantly increasing the grab or friction of the brake caliper pads. They are also there to displace water, as the front end is quite exposed to wet, unlike a car. Early japanese bikes had solid discs, and they did not work at all for the first few squeezes after the bike was rolling when wet. Scary. In fact they were so bad, that a warning sticker could often be found on the fork leg attesting to proper break in procedures when first taking off in rainy conditions. Hot rodders on these early bikes would often have holes drilled in the solid rotors for these reasons. It is of course now standard, all the bike companies do this. The holes also aid in cooling as well, helping to vent air to more of the metal that comprises the disc.
