Quote:
Originally Posted by CyberFormula
I already said I vote for blanks...
but the new question is....
Why do Motor bikes have Drilled.  |
Bikes are extremely light and are generally equipped with about three rotors. Therefore, the rotors don't need nearly as much heat capacity as cars and generally won't get as hot. However, what the bikes do need is a rotor with a large enough diameter to provide the needed braking force. As the rotor outer diameter gets larger, the force exerted also gets larger. (For a demonstration of this concept, spin a CD and try to stop it by putting a finger near the center of the CD. Then do it again, but this time put your finger at the very outer edge of the CD. You should notice a dramatic difference in the force needed to stop the CD.)
Therefore, the bikes want a large outer diameter, but since they're so light, they don't need the thermal capacity that comes from a full solid hunk of metal. Thus, here drilling for weight savings is more acceptable.
Also, note that bike rotors are not vented. Since there are no internal vanes, that means that the percentage weight savings gain from drilling is increased. Bikes rotors generally have a much larger portion of their rotors drilled out than car rotors.
Finally, when the stresses get really high, bikes revert back to solid rotors. See e.g. MotoGP rotors.