On 16/11/17 20:38, David Scheidt wrote:
Tosspot wrote:
:Why do they have holes in them?

:Car discs don't, motorbike discs don't, aircraft discs don't. Why do
:bicycle discs have them?

Lots of high-performance car brake rotors are drilled or slotted.
Slotting is more common on better stuff, holes can crack. They serve
a couple of features. One, people think they're cool. two, they
allow the gasses that come off brake pads somewhere to go (this is a
non-issue with modern pads, but it was a problem in the dark ages).
Three, they give water somewhere to go. Four, they improve cooling
(increase surface area). five, the clean pads, and reduce wear.

Gasses off a bicycle pad? Really?

Nobody drills rims, and most[1] motorbikes, which are exposed to the
rain don't.

Because 75 kg of me at 30 kph is the same KE as 160 kph Audi at 1.5
tonnes? Nah.

Hmmm...could it be it helps to clean them? They aren't dissipating the
KE, so they don't get Eeek! hot. But surely the crud would build up in
the holes?

I'm going to order a solid one for the front and fit it in the spring
and see if it makes any difference.

[1] In deference to John B.